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Dr. Carleen Eaton utilizes her M.D. from the UCLA School of Medicine to bring in real world applications and examples for her AP Biology class. Carleen covers all the AP tested topics from cell structure to evolution to the laboratory review. Dr. Eaton has been teaching math and science for over 10 years and has won numerous "Teacher of the Year" awards and is consistently ranked as one of the top instructors in California. This course is indispensable for the student looking to ace the AP Biology test as Carleen covers the important concepts with fully illustrated diagrams before going in-depth into problems encountered in the multiple choice and free response sections. Additional topics also include Cell Structure, Genetics, Plants, Physiology, Behavior, and Ecology. Course has been updated to the newest 2013+ standards, with videos covering the changes (Section 15), as well as a practice test walk-through (Section 16).

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I. Chemistry of Life
  Elements, Compounds, and Chemical Bonds 56:18
   Intro 0:00 
   Elements 0:09 
    Elements 0:48 
    Matter 0:55 
    Naturally Occurring Elements 1:12 
    Atomic Number and Atomic Mass 2:39 
   Compounds 3:06 
    Molecule 3:07 
    Compounds 3:14 
    Examples 3:20 
   Atoms 4:53 
    Atoms 4:56 
    Protons, Neutrons, and Electrons 5:29 
    Isotopes 10:42 
   Energy Levels of Electrons 13:01 
    Electron Shells 13:13 
    Valence Shell 13:22 
    Example: Electron Shells and Potential Energy 13:28 
   Covalent Bonds 19:52 
    Covalent Bonds 19:54 
    Examples 20:03 
   Polar and Nonpolar Covalent Bonds 23:54 
    Polar Bond 24:07 
    Nonpolar Bonds 24:17 
    Examples 24:25 
   Ionic Bonds 29:04 
    Ionic Bond, Cations, Anions 29:19 
    Example: NaCl 29:30 
   Hydrogen Bond 33:18 
    Hydrogen Bond 33:20 
   Chemical Reactions 35:36 
    Example: Reactants, Products and Chemical Reactions 35:45 
   Molecular Mass and Molar Concentration 38:45 
    Avogadro's Number and Mol 39:12 
    Examples: Molecular Mass and Molarity 42:10 
   Example 1: Proton, Neutrons and Electrons 47:05 
   Example 2: Reactants and Products 49:35 
   Example 3: Bonding 52:39 
   Example 4: Mass 53:59 
  Properties of Water 50:23
   Intro 0:00 
   Molecular Structure of Water 0:21 
    Molecular Structure of Water 0:27 
   Properties of Water 4:30 
    Cohesive 4:55 
    Transpiration 5:29 
    Adhesion 6:20 
    Surface Tension 7:17 
   Properties of Water, cont. 9:14 
    Specific Heat 9:25 
    High Heat Capacity 13:24 
    High Heat of Evaporation 16:42 
   Water as a Solvent 21:13 
    Solution 21:28 
    Solvent 21:48 
    Example: Water as a Solvent 22:22 
   Acids and Bases 25:40 
    Example 25:41 
   pH 36:30 
    pH Scale: Acidic, Neutral, and Basic 36:35 
   Example 1: Molecular Structure and Properties of Water 41:18 
   Example 2: Special Properties of Water 42:53 
   Example 3: pH Scale 44:46 
   Example 4: Acids and Bases 46:19 
  Organic Compounds 53:54
   Intro 0:00 
   Organic Compounds 0:09 
    Organic Compounds 0:11 
    Inorganic Compounds 0:15 
    Examples: Organic Compounds 1:15 
   Isomers 5:52 
    Isomers 5:55 
    Structural Isomers 6:23 
    Geometric Isomers 8:14 
    Enantiomers 9:55 
   Functional Groups 12:46 
    Examples: Functional Groups 12:59 
    Amino Group 13:51 
    Carboxyl Group 14:38 
    Hydroxyl Group 15:22 
    Methyl Group 16:14 
    Carbonyl Group 16:30 
    Phosphate Group 17:51 
   Carbohydrates 18:26 
    Carbohydrates 19:07 
    Example: Monosaccharides 21:12 
   Carbohydrates, cont. 24:11 
    Disaccharides, Polysaccharides and Examples 24:21 
   Lipids 35:52 
    Examples of Lipids 36:04 
    Saturated and Unsaturated 38:57 
   Phospholipids 43:26 
    Phospholipids 43:29 
    Example 43:34 
   Steroids 46:24 
    Cholesterol 46:28 
   Example 1: Isomers 48:11 
   Example 2: Functional Groups 50:45 
   Example 3: Galactose, Ketose, and Aldehyde Sugar 52:24 
   Example 4: Class of Molecules 53:06 
  Nucleic Acids and Proteins 37:23
   Intro 0:00 
   Nucleic Acids 0:09 
    Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) 0:29 
   Nucleic Acids, cont. 2:56 
    Purines 3:10 
    Pyridines 3:32 
   Double Helix 4:59 
    Double Helix and Example 5:01 
   Proteins 12:33 
    Amino Acids and Polypeptides 12:39 
    Examples: Amino Acid 13:25 
   Polypeptide Formation 18:09 
    Peptide Bonds 18:14 
    Primary Structure 18:35 
   Protein Structure 23:19 
    Secondary Structure 23:22 
    Alpha Helices and Beta Pleated Sheets 23:34 
   Protein Structure 25:43 
    Tertiary Structure 25:44 
    5 Types of Interaction 26:56 
   Example 1: Complementary DNA Strand 31:45 
   Example 2: Differences Between DNA and RNA 33:19 
   Example 3: Amino Acids 34:32 
   Example 4: Tertiary Structure of Protein 35:46 
II. Cell Structure and Function
  Cell Types (Prokaryotic and Eukaryotic) 45:50
   Intro 0:00 
   Cell Theory and Cell Types 0:12 
    Cell Theory 0:13 
    Prokaryotic and Eukaryotic Cells 0:36 
    Endosymbiotic Theory 1:13 
   Study of Cells 4:07 
    Tools and Techniques 4:08 
    Light Microscopes 5:08 
    Light vs. Electron Microscopes: Magnification 5:18 
    Light vs. Electron Microscopes: Resolution 6:26 
    Light vs. Electron Microscopes: Specimens 7:53 
    Electron Microscopes: Transmission and Scanning 8:28 
    Cell Fractionation 10:01 
    Cell Fractionation Step 1: Homogenization 10:33 
    Cell Fractionation Step 2: Spin 11:24 
    Cell Fractionation Step 3: Differential Centrifugation 11:53 
   Comparison of Prokaryotic and Eukaryotic Cells 14:12 
    Prokaryotic vs. Eukaryotic Cells: Domains 14:43 
    Prokaryotic vs. Eukaryotic Cells: Plasma Membrane 15:40 
    Prokaryotic vs. Eukaryotic Cells: Cell Walls 16:15 
    Prokaryotic vs. Eukaryotic Cells: Genetic Materials 16:38 
    Prokaryotic vs. Eukaryotic Cells: Structures 17:28 
    Prokaryotic vs. Eukaryotic Cells: Unicellular and Multicellular 18:19 
    Prokaryotic vs. Eukaryotic Cells: Size 18:31 
    Plasmids 18:52 
   Prokaryotic vs. Eukaryotic Cells 19:22 
    Nucleus 19:24 
    Organelles 19:48 
    Cytoskeleton 20:02 
    Cell Wall 20:35 
    Ribosomes 20:57 
    Size 21:37 
   Comparison of Plant and Animal Cells 22:15 
    Plasma Membrane 22:55 
    Plant Cells Only: Cell Walls 23:12 
    Plant Cells Only: Central Vacuole 25:08 
    Animal Cells Only: Centrioles 26:40 
    Animal Cells Only: Lysosomes 27:43 
   Plant vs. Animal Cells 29:16 
    Overview of Plant and Animal Cells 29:17 
   Evidence for the Endosymbiotic Theory 30:52 
    Characteristics of Mitochondria and Chloroplasts 30:54 
   Example 1: Prokaryotic vs. Eukaryotic Cells 35:44 
   Example 2: Endosymbiotic Theory and Evidence 38:38 
   Example 3: Plant and Animal Cells 41:49 
   Example 4: Cell Fractionation 43:44 
  Subcellular Structure 59:38
   Intro 0:00 
   Prokaryotic Cells 0:09 
    Shapes of Prokaryotic Cells 0:22 
    Cell Wall 1:19 
    Capsule 3:23 
    Pili/Fimbria 3:54 
    Flagella 4:35 
    Nucleoid 6:16 
    Plasmid 6:37 
    Ribosomes 7:09 
   Eukaryotic Cells (Animal Cell Structure) 8:01 
    Plasma Membrane 8:13 
    Microvilli 8:48 
    Nucleus 9:47 
    Nucleolus 11:06 
    Ribosomes: Free and Bound 12:26 
    Rough Endoplasmic Reticulum (RER) 13:43 
   Eukaryotic Cells (Animal Cell Structure), cont. 14:51 
    Endoplasmic Reticulum: Smooth and Rough 15:08 
    Golgi Apparatus 17:55 
    Vacuole 20:43 
    Lysosome 22:01 
    Mitochondria 25:40 
    Peroxisomes 28:18 
   Cytoskeleton 30:41 
    Cytoplasm and Cytosol 30:53 
    Microtubules: Centrioles, Spindel Fibers, Clagell, Cillia 32:06 
    Microfilaments 36:39 
    Intermediate Filaments and Kerotin 38:52 
   Eukaryotic Cells (Plant Cell Structure) 40:08 
    Plasma Membrane, Primary Cell Wall, and Secondary Cell Wall 40:30 
    Middle Lamella 43:21 
    Central Cauole 44:12 
    Plastids: Leucoplasts, Chromoplasts, Chrloroplasts 45:35 
    Chloroplasts 47:06 
   Example 1: Structures and Functions 48:46 
   Example 2: Cell Walls 51:19 
   Example 3: Cytoskeleton 52:53 
   Example 4: Antibiotics and the Endosymbiosis Theory 56:55 
  Cell Membranes and Transport 53:10
   Intro 0:00 
   Cell Membrane Structure 0:09 
    Phospholipids Bilayer 0:11 
    Chemical Structure: Amphipathic and Fatty Acids 0:25 
   Cell Membrane Proteins 2:44 
    Fluid Mosaic Model 2:45 
    Peripheral Proteins and Integral Proteins 3:19 
    Transmembrane Proteins 4:34 
    Cholesterol 4:48 
    Functions of Membrane Proteins 6:39 
   Transport Across Cell Membranes 9:52 
    Transport Across Cell Membranes 9:53 
   Methods of Passive Transport 12:07 
    Passive and Active Transport 12:08 
    Simple Diffusion 12:45 
    Facilitated Diffusion 15:20 
   Osmosis 17:17 
    Definition and Example of Osmosis 17:18 
    Hypertonic, Hypotonic, and Isotonic 21:47 
   Active Transport 27:57 
    Active Transport 28:17 
    Sodium and Potassium Pump 29:45 
    Cotransport 34:38 
    2 Types of Active Transport 37:09 
   Endocytosis and Exocytosis 37:38 
    Endocytosis and Exocytosis 37:51 
    Types of Endocytosis: Pinocytosis 40:39 
    Types of Endocytosis: Phagocytosis 41:02 
   Receptor Mediated Endocytosis 41:27 
    Receptor Mediated Endocytosis 41:28 
   Example 1: Cell Membrane and Permeable Substances 43:59 
   Example 2: Osmosis 45:20 
   Example 3: Active Transport, Cotransport, Simple and Facilitated Diffusion 47:36 
   Example 4: Match Terms with Definition 50:55 
  Cellular Communication 57:09
   Intro 0:00 
   Extracellular Matrix 0:28 
    The Extracellular Matrix (ECM) 0:29 
    ECM in Animal Cells 0:55 
    Fibronectin and Integrins 1:34 
   Intercellular Communication in Plants 2:48 
    Intercellular Communication in Plants: Plasmodesmata 2:50 
   Cell to Cell Communication in Animal Cells 3:39 
    Cell Junctions 3:42 
    Desmosomes 3:54 
    Tight Junctions 5:07 
    Gap Junctions 7:00 
   Cell Signaling 8:17 
    Cell Signaling: Ligand and Signal Transduction Pathway 8:18 
    Direct Contact 8:48 
    Over Distances Contact and Hormones 10:09 
   Stages of Cell Signaling 11:53 
    Reception Phase 11:54 
    Transduction Phase 13:49 
    Response Phase 14:45 
   Cell Membrane Receptors 15:37 
    G-Protein Coupled Receptor 15:38 
   Cell Membrane Receptor, Cont. 21:37 
    Receptor Tyrosine Kinases (RTKs) 21:38 
    Autophosphorylation, Monomer, and Dimer 22:57 
   Cell Membrane Receptor, Cont. 27:01 
    Ligand-Gated Ion Channels 27:02 
   Intracellular Receptors 29:43 
    Intracellular Receptor and Receptor -Ligand Complex 29:44 
   Signal Transduction 32:57 
    Signal Transduction Pathways 32:58 
    Adenylyl Cyclase and cAMP 35:53 
   Second Messengers 39:18 
     cGMP, Inositol Trisphosphate, and Diacylglycerol 39:20 
   Cell Response 45:15 
    Cell Response 45:16 
    Apoptosis 46:57 
   Example 1: Tight Junction and Gap Junction 48:29 
   Example 2: Three Phases of Cell Signaling 51:48 
   Example 3: Ligands and Binding of Hormone 54:03 
   Example 4: Signal Transduction 56:06 
III. Cell Division
  The Cell Cycle 37:49
   Intro 0:00 
   Functions of Cell Division 0:09 
    Overview of Cell Division: Reproduction, Growth, and Repair 0:11 
    Important Term: Daughter Cells 2:25 
   Chromosome Structure 3:36 
    Chromosome Structure: Sister Chromatids and Centromere 3:37 
    Chromosome Structure: Chromatin 4:31 
    Chromosome with One Chromatid or Two Chromatids 5:25 
    Chromosome Structure: Long and Short Arm 6:49 
   Mitosis and Meiosis 7:00 
    Mitosis 7:41 
    Meiosis 8:40 
   The Cell Cycle 10:43 
    Mitotic Phase and Interphase 10:44 
   Cytokinesis 15:51 
    Cytokinesis in Animal Cell: Cleavage Furrow 15:52 
    Cytokinesis in Plant Cell: Cell Plate 17:28 
   Control of the Cell Cycle 18:28 
    Cell Cycle Control System and Checkpoints 18:29 
   Cyclins and Cyclin Dependent Kinases 21:18 
    Cyclins and Cyclin Dependent Kinases (CDKSs) 21:20 
    MPF 23:17 
    Internal Factor Regulating Cell Cycle 24:00 
    External Factor Regulating Cell Cycle 24:53 
    Contact Inhibition and Anchorage Dependent 25:53 
   Cancer and the Cell Cycle 27:42 
    Cancer Cells 27:46 
   Example1: Parts of the Chromosome 30:15 
   Example 2: Cell Cycle 31:50 
   Example 3: Control of the Cell Cycle 33:32 
   Example 4: Cancer and the Cell 35:01 
  Mitosis 35:01
   Intro 0:00 
   Review of the Cell Cycle 0:09 
    Interphase: G1 Phase 0:34 
    Interphase: S Phase 0:56 
    Interphase: G2 Phase 1:31 
    M Phase: Mitosis and Cytokinesis 1:47 
   Overview of Mitosis 3:08 
    What is Mitosis? 3:10 
    Overview of Mitosis 3:17 
    Diploid and Haploid 5:37 
    Homologous Chromosomes 6:04 
   The Spindle Apparatus 11:57 
    The Spindle Apparatus 12:00 
    Centrosomes and Centrioles 12:40 
    Microtubule Organizing Center 13:03 
    Spindle Fiber of Spindle Microtubules 13:23 
    Kinetochores 14:06 
    Asters 15:45 
   Prophase 16:47 
    First Phase of Mitosis: Prophase 16:54 
   Metaphase 20:05 
    Second Phase of Mitosis: Metaphase 20:10 
   Anaphase 22:52 
    Third Phase of Mitosis: Anaphase 22:53 
   Telophase and Cytokinesis 24:34 
    Last Phase of Mitosis: Telophase and Cytokinesis 24:35 
   Summary of Mitosis 27:46 
    Summary of Mitosis 27:47 
   Example 1: Spindle Apparatus 28:50 
   Example 2: Last Phase of Mitosis 30:39 
   Example 3: Prophase 32:41 
   Example 4: Identify the Phase 33:52 
  Meiosis 1:00:58
   Intro 0:00 
   Haploid and Diploid Cells 0:09 
    Diploid and Somatic Cells 0:29 
    Haploid and Gametes 1:20 
    Example: Human Cells and Chromosomes 1:41 
    Sex Chromosomes 6:00 
   Comparison of Mitosis and Meiosis 10:42 
    Mitosis Vs. Meiosis: Cell Division 10:59 
    Mitosis Vs. Meiosis: Daughter Cells 12:31 
    Meiosis: Pairing of Homologous Chromosomes 13:40 
   Mitosis and Meiosis 14:21 
    Process of Mitosis 14:27 
    Process of Meiosis 16:12 
   Synapsis and Crossing Over 19:14 
    Prophase I: Synapsis and Crossing Over 19:15 
    Chiasmata 22:33 
   Meiosis I 25:49 
    Prophase I: Crossing Over 25:50 
    Metaphase I: Homologs Line Up 26:00 
    Anaphase I: Homologs Separate 28:16 
    Telophase I and Cytokinesis 29:15 
    Independent Assortment 30:58 
   Meiosis II 32:17 
    Propphase II 33:50 
    Metaphase II 34:06 
    Anaphase II 34:50 
    Telophase II 36:09 
    Cytokinesis 37:00 
   Summary of Meiosis 38:15 
    Summary of Meiosis 38:16 
    Cell Division Mechanism in Plants 41:57 
   Example 1: Cell Division and Meiosis 46:15 
   Example 2: Phases of Meiosis 50:22 
   Example 3: Label the Figure 54:29 
   Example 4: Four Differences Between Mitosis and Meiosis 56:37 
IV. Cellular Energetics
  Enzymes 51:03
   Intro 0:00 
   Law of Thermodynamics 0:08 
    Thermodynamics 0:09 
    The First Law of Thermodynamics 0:37 
    The Second Law of Thermodynamics 1:24 
    Entropy 1:35 
   The Gibbs Free Energy Equation 3:07 
    The Gibbs Free Energy Equation 3:08 
   ATP 8:23 
    Adenosine Triphosphate (ATP) 8:24 
    Cellular Respiration 11:32 
    Catabolic Pathways 12:28 
    Anabolic Pathways 12:54 
   Enzymes 14:31 
    Enzymes 14:32 
    Enzymes and Exergonic Reaction 14:40 
    Enzymes and Endergonic Reaction 16:36 
   Enzyme Specificity 21:29 
    Substrate 21:41 
    Induced Fit 23:04 
   Factors Affecting Enzyme Activity 25:55 
    Substrate Concentration 26:07 
    pH 27:10 
    Temperature 29:14 
    Presence of Cofactors 29:57 
   Regulation of Enzyme Activity 31:12 
    Competitive Inhibitors 32:13 
    Noncompetitive Inhibitors 33:52 
    Feedback Inhibition 35:22 
   Allosteric Interactions 36:56 
    Allosteric Regulators 37:00 
   Example 1: Is the Inhibitor Competitive or Noncompetitive? 40:49 
   Example 2: Thermophiles 44:18 
   Example 3: Exergonic or Endergonic 46:09 
   Example 4: Energy Vs. Reaction Progress Graph 48:47 
  Glycolysis and Anaerobic Respiration 38:01
   Intro 0:00 
   Cellular Respiration Overview 0:13 
    Cellular Respiration 0:14 
    Anaerobic Respiration vs. Aerobic Respiration 3:50 
   Glycolysis Overview 4:48 
    Overview of Glycolysis 4:50 
   Glycolysis Involves a Redox Reaction 7:02 
    Redox Reaction 7:04 
   Glycolysis 15:04 
    Important Facts About Glycolysis 15:07 
    Energy Invested Phase 16:12 
    Splitting of Fructose 1,6-Phosphate and Energy Payoff Phase 17:50 
    Substrate Level Phophorylation 22:12 
   Aerobic Versus Anaerobic Respiration 23:57 
    Aerobic Versus Anaerobic Respiration 23:58 
   Cellular Respiration Overview 27:15 
    When Cellular Respiration is Anaerobic 27:17 
    Glycolysis 28:26 
    Alcohol Fermentation 28:45 
    Lactic Acid Fermentation 29:58 
   Example 1: Glycolysis 31:04 
   Example 2: Glycolysis, Fermentation and Anaerobic Respiration 33:44 
   Example 3: Aerobic Respiration Vs. Anaerobic Respiration 35:25 
   Example 4: Exergonic Reaction and Endergonic Reaction 36:42 
  Aerobic Respiration 51:06
   Intro 0:00 
   Aerobic Vs. Anaerobic Respiration 0:06 
    Aerobic and Anaerobic Comparison 0:07 
   Review of Glycolysis 1:48 
    Overview of Glycolysis 2:06 
    Glycolysis: Energy Investment Phase 2:25 
    Glycolysis: Energy Payoff Phase 2:58 
   Conversion of Pyruvate to Acetyl CoA 4:55 
    Conversion of Pyruvate to Acetyl CoA 4:56 
    Energy Formation 8:06 
   Mitochondrial Structure 8:58 
    Endosymbiosis Theory 9:23 
    Matrix 10:00 
    Outer Membrane, Inner Membrane, and Intermembrane Space 10:43 
    Cristae 11:47 
   The Citric Acid Cycle 12:11 
    The Citric Acid Cycle (Also Called Krebs Cycle) 12:12 
    Substrate Level Phosphorylation 18:47 
   Summary of ATP, NADH, and FADH2 Production 23:13 
    Process: Glycolysis 23:28 
    Process: Acetyl CoA Production 23:36 
    Process: Citric Acid Cycle 23:52 
   The Electron Transport Chain 24:24 
    Oxidative Phosphorylation 24:28 
    The Electron Transport Chain and ATP Synthase 25:20 
    Carrier Molecules: Cytochromes 27:18 
    Carrier Molecules: Flavin Mononucleotide (FMN) 28:05 
   Chemiosmosis 32:46 
    The Process of Chemiosmosis 32:47 
   Summary of ATP Produced by Aerobic Respiration 38:24 
    ATP Produced by Aerobic Respiration 38:27 
   Example 1: Aerobic Respiration 43:38 
   Example 2: Label the Location for Each Process and Structure 45:08 
   Example 3: The Electron Transport Chain 47:06 
   Example 4: Mitochondrial Inner Membrane 48:38 
  Photosynthesis 1:02:52
   Intro 0:00 
   Photosynthesis 0:09 
    Introduction to Photosynthesis 0:10 
    Autotrophs and Heterotrophs 0:25 
    Overview of Photosynthesis Reaction 1:05 
   Leaf Anatomy and Chloroplast Structure 2:54 
    Chloroplast 2:55 
    Cuticle 3:16 
    Upper Epidermis 3:27 
    Mesophyll 3:40 
    Stomates 4:00 
    Guard Cells 4:45 
    Transpiration 5:01 
    Vascular Bundle 5:20 
    Stroma and Double Membrane 6:20 
    Grana 7:17 
    Thylakoids 7:30 
    Dark Reaction and Light Reaction 7:46 
   Light Reactions 8:43 
    Light Reactions 8:47 
    Pigments: Chlorophyll a, Chlorophyll b, and Carotenoids 9:19 
    Wave and Particle 12:10 
    Photon 12:34 
   Photosystems 13:24 
    Photosystems 13:28 
    Reaction-Center Complex and Light Harvesting Complexes 14:01 
   Noncyclic Photophosphorylation 17:46 
    Noncyclic Photophosphorylation Overview 17:47 
    What is Photophosphorylation? 18:25 
    Noncyclic Photophosphorylation Process 19:07 
    Photolysis and The Rest of Noncyclic Photophosphorylation 21:33 
   Cyclic Photophosphorylation 31:45 
    Cyclic Photophosphorylation 31:46 
   Light Independent Reactions 34:34 
    The Calvin Cycle 34:35 
   C3 Plants and Photorespiration 40:31 
    C3 Plants and Photorespiration 40:32 
   C4 Plants 45:32 
    C4 Plants: Structures and Functions 45:33 
   CAM Plants 50:25 
    CAM Plants: Structures and Functions 50:35 
   Example 1: Calvin Cycle 54:34 
   Example 2: C4 Plant 55:48 
   Example 3: Photosynthesis and Photorespiration 58:35 
   Example 4: CAM Plants 60:41 
V. Molecular Genetics
  DNA Synthesis 38:45
   Intro 0:00 
   Review of DNA Structure 0:09 
    DNA Molecules 0:10 
    Nitrogenous Base: Pyrimidines and Purines 1:25 
   DNA Double Helix 3:03 
    Complementary Strands of DNA 3:12 
    5' to 3' & Antiparallel 4:55 
   Overview of DNA Replication 7:10 
    DNA Replication & Semiconservative 7:11 
   DNA Replication 10:26 
    Origin of Replication 10:28 
    Helicase 11:10 
    Single-Strand Binding Protein 12:05 
    Topoisomerases 13:14 
    DNA Polymerase 14:26 
    Primase 15:55 
   Leading and Lagging Strands 16:51 
    Leading Strand and Lagging Strand 16:52 
    Okazaki Fragments 18:10 
    DNA Polymerase I 20:11 
    Ligase 21:12 
   Proofreading and Mismatch Repair 22:18 
    Proofreading 22:19 
    Mismatch 23:33 
   Telomeres 24:58 
    Telomeres 24:59 
   Example 1: Function of Enzymes During DNA Synthesis 28:09 
   Example 2: Accuracy of the DNA Sequence 31:42 
   Example 3: Leading Strand and Lagging Strand 32:38 
   Example 4: Telomeres 35:40 
  Transcription and Translation 1:17:01
   Intro 0:00 
   Transcription and Translation Overview 0:07 
    From DNA to RNA to Protein 0:09 
   Structure and Types of RNA 3:14 
    Structure and Types of RNA 3:33 
    mRNA 6:19 
    rRNA 7:02 
    tRNA 7:28 
   Transcription 7:54 
    Initiation Phase 8:11 
    Elongation Phase 12:12 
    Termination Phase 14:51 
   RNA Processing 16:11 
    Types of RNA Processing 16:12 
    Exons and Introns 16:35 
    Splicing & Spliceosomes 18:27 
    Addition of a 5' Cap and a Poly A tail 20:41 
    Alternative Splicing 21:43 
   Translation 23:41 
    Nucleotide Triplets or Codons 23:42 
    Start Codon 25:24 
    Stop Codons 25:38 
    Coding of Amino Acids and Wobble Position 25:57 
   Translation Cont. 28:29 
    Transfer RNA (tRNA): Structures and Functions 28:30 
   Ribosomes 35:15 
    Peptidyl, Aminoacyl, and Exit Site 35:23 
   Steps of Translation 36:58 
    Initiation Phase 37:12 
    Elongation Phase 43:12 
    Termination Phase 45:28 
   Mutations 49:43 
    Types of Mutations 49:44 
    Substitutions: Silent 51:11 
    Substitutions: Missense 55:27 
    Substitutions: Nonsense 59:37 
    Insertions and Deletions 61:10 
   Example 1: Three Types of Processing that are Performed on pre-mRNA 66:53 
   Example 2: The Process of Translation 69:10 
   Example 3: Transcription 72:04 
   Example 4: Three Types of Substitution Mutations 74:09 
  Viral Structure and Genetics 43:12
   Intro 0:00 
   Structure of Viruses 0:09 
    Structure of Viruses: Capsid and Envelope 0:10 
    Bacteriophage 1:48 
    Other Viruses 2:28 
   Overview of Viral Reproduction 3:15 
    Host Range 3:48 
    Step 1: Bind to Host Cell 4:39 
    Step 2: Viral Nuclei Acids Enter the Cell 5:15 
    Step 3: Viral Nucleic Acids & Proteins are Synthesized 5:54 
    Step 4: Virus Assembles 6:34 
    Step 5: Virus Exits the Cell 6:55 
   The Lytic Cycle 7:37 
    Steps in the Lytic Cycle 7:38 
   The Lysogenic Cycle 11:27 
    Temperate Phage 11:34 
    Steps in the Lysogenic Cycle 12:09 
   RNA Viruses 16:57 
    Types of RNA Viruses 17:15 
    Positive Sense 18:16 
    Negative Sense 18:48 
    Reproductive Cycle of RNA Viruses 19:32 
   Retroviruses 25:48 
    Complementary DNA (cDNA) & Reverse Transcriptase 25:49 
    Life Cycle of a Retrovirus 28:22 
   Prions 32:42 
    Prions: Definition and Examples 32:45 
    Viroids 34:46 
   Example 1: The Lytic Cycle 35:37 
   Example 2: Retrovirus 38:03 
   Example 3: Positive Sense RNA vs. Negative Sense RNA 39:10 
   Example 4: The Lysogenic Cycle 40:42 
  Bacterial Genetics and Gene Regulation 49:45
   Intro 0:00 
   Bacterial Genomes 0:09 
    Structure of Bacterial Genomes 0:16 
   Transformation 1:22 
    Transformation 1:23 
    Vector 2:49 
   Transduction 3:32 
    Process of Transduction 3:38 
   Conjugation 8:06 
    Conjugation & F factor 8:07 
   Operons 14:02 
    Definition and Example of Operon 14:52 
    Structural Genes 16:23 
    Promoter Region 17:04 
    Regulatory Protein & Operators 17:53 
   The lac Operon 20:09 
    The lac Operon: Inducible System 20:10 
   The trp Operon 28:02 
    The trp Operon: Repressible System 28:03 
    Corepressor 31:37 
    Anabolic & Catabolic 33:12 
   Positive Regulation of the lac Operon 34:39 
    Positive Regulation of the lac Operon 34:40 
   Example 1: The Process of Transformation 39:07 
   Example 2: Operon & Terms 43:29 
   Example 3: Inducible lac Operon and Repressible trp Operon 45:15 
   Example 4: lac Operon 47:10 
  Eukaryotic Gene Regulation and Mobile Genetic Elements 54:26
   Intro 0:00 
   Mechanism of Gene Regulation 0:11 
    Differential Gene Expression 0:13 
    Levels of Regulation 2:24 
   Chromatin Structure and Modification 4:35 
    Chromatin Structure 4:36 
    Levels of Packing 5:50 
    Euchromatin and Heterochromatin 8:58 
    Modification of Chromatin Structure 9:58 
    Epigenetic 12:49 
   Regulation of Transcription 14:20 
    Promoter Region, Exon, and Intron 14:26 
    Enhancers: Control Element 15:31 
    Enhancer & DNA-Bending Protein 17:25 
    Coordinate Control 21:23 
    Silencers 23:01 
   Post-Transcriptional Regulation 24:05 
    Post-Transcriptional Regulation 24:07 
    Alternative Splicing 27:19 
    Differences in mRNA Stability 28:02 
    Non-Coding RNA Molecules: micro RNA & siRNA 30:01 
   Regulation of Translation and Post-Translational Modifications 32:31 
    Regulation of Translation and Post-Translational Modifications 32:55 
    Ubiquitin 35:21 
    Proteosomes 36:04 
   Transposons 37:50 
    Mobile Genetic Elements 37:56 
    Barbara McClintock 38:37 
    Transposons & Retrotransposons 40:38 
    Insertion Sequences 43:14 
    Complex Transposons 43:58 
   Example 1: Four Mechanisms that Decrease Production of Protein 45:13 
   Example 2: Enhancers and Gene Expression 49:09 
   Example 3: Primary Transcript 50:41 
   Example 4: Retroviruses and Retrotransposons 52:11 
  Biotechnology 49:26
   Intro 0:00 
   Definition of Biotechnology 0:08 
    Biotechnology 0:09 
    Genetic Engineering 1:05 
    Example: Golden Corn 1:57 
   Recombinant DNA 2:41 
    Recombinant DNA 2:42 
    Transformation 3:24 
    Transduction 4:24 
    Restriction Enzymes, Restriction Sites, & DNA Ligase 5:32 
   Gene Cloning 13:48 
    Plasmids 14:20 
    Gene Cloning: Step 1 17:35 
    Gene Cloning: Step 2 17:57 
    Gene Cloning: Step 3 18:53 
    Gene Cloning: Step 4 19:46 
   Gel Electrophoresis 27:25 
    What is Gel Electrophoresis? 27:26 
    Gel Electrophoresis: Step 1 28:13 
    Gel Electrophoresis: Step 2 28:24 
    Gel Electrophoresis: Step 3 & 4 28:39 
    Gel Electrophoresis: Step 5 29:55 
    Southern Blotting 31:25 
   Polymerase Chain Reaction (PCR) 32:11 
    Polymerase Chain Reaction (PCR) 32:12 
    Denaturing Phase 35:40 
    Annealing Phase 36:07 
    Elongation/ Extension Phase 37:06 
   DNA Sequencing and the Human Genome Project 39:19 
    DNA Sequencing and the Human Genome Project 39:20 
   Example 1: Gene Cloning 40:40 
   Example 2: Recombinant DNA 43:04 
   Example 3: Match Terms With Descriptions 45:43 
   Example 4: Polymerase Chain Reaction 47:36 
VI. Heredity
  Mendelian Genetics 1:32:08
   Intro 0:00 
   Background 0:40 
    Gregory Mendel & Mendel's Law 0:41 
    Blending Hypothesis 1:04 
    Particulate Inheritance 2:08 
   Terminology 2:55 
    Gene 3:05 
    Locus 3:57 
    Allele 4:37 
    Dominant Allele 5:48 
    Recessive Allele 7:38 
    Genotype 9:22 
    Phenotype 10:01 
    Homozygous 10:44 
    Heterozygous 11:39 
    Penetrance 11:57 
    Expressivity 14:15 
   Mendel's Experiments 15:31 
    Mendel's Experiments: Pea Plants 15:32 
   The Law of Segregation 21:16 
    Mendel's Conclusions 21:17 
    The Law of Segregation 22:57 
   Punnett Squares 28:27 
    Using Punnet Squares 28:30 
   The Law of Independent Assortment 32:35 
    Monohybrid 32:38 
    Dihybrid 33:29 
    The Law of Independent Assortment 34:00 
   The Law of Independent Assortment, cont. 38:13 
    The Law of Independent Assortment: Punnet Squares 38:29 
   Meiosis and Mendel's Laws 43:38 
    Meiosis and Mendel's Laws 43:39 
   Test Crosses 49:07 
    Test Crosses Example 49:08 
   Probability: Multiplication Rule and the Addition Rule 53:39 
    Probability Overview 53:40 
    Independent Events & Multiplication Rule 55:40 
    Mutually Exclusive Events & Addition Rule 60:25 
   Incomplete Dominance, Codominance and Multiple Alleles 62:55 
    Incomplete Dominance 62:56 
   Incomplete Dominance, Codominance and Multiple Alleles 67:06 
    Codominance and Multiple Alleles 67:08 
   Polygenic Inheritance and Pleoitropy 70:19 
    Polygenic Inheritance and Pleoitropy 70:26 
   Epistasis 72:51 
    Example of Epistasis 72:52 
   Example 1: Genetic of Eye Color and Height 77:39 
   Example 2: Blood Type 81:57 
   Example 3: Pea Plants 85:09 
   Example 4: Coat Color 88:34 
  Linked Genes and Non-Mendelian Modes of Inheritance 39:38
   Intro 0:00 
   Review of the Law of Independent Assortment 0:14 
    Review of the Law of Independent Assortment 0:24 
   Linked Genes 6:06 
    Linked Genes 6:07 
    Bateson & Pannett: Pea Plants 8:00 
   Crossing Over and Recombination 15:17 
    Crossing Over and Recombination 15:18 
   Extranuclear Genes 20:50 
    Extranuclear Genes 20:51 
    Cytoplasmic Genes 21:31 
   Genomic Imprinting 23:45 
    Genomic Imprinting 23:58 
    Methylation 24:43 
   Example 1: Recombination Frequencies & Linkage Map 27:07 
   Example 2: Linked Genes 28:39 
   Example 3: Match Terms to Correct Descriptions 36:46 
   Example 4: Leber's Optic Neuropathy 38:40 
  Sex-Linked Traits and Pedigree Analysis 43:39
   Intro 0:00 
   Sex-Linked Traits 0:09 
    Human Chromosomes, XY, and XX 0:10 
    Thomas Morgan's Drosophila 1:44 
   X-Inactivation and Barr Bodies 14:48 
    X-Inactivation Overview 14:49 
    Calico Cats Example 17:04 
   Pedigrees 19:24 
    Definition and Example of Pedigree 19:25 
   Autosomal Dominant Inheritance 20:51 
    Example: Huntington's Disease 20:52 
   Autosomal Recessive Inheritance 23:04 
    Example: Cystic Fibrosis, Tay-Sachs Disease, and Phenylketonuria 23:05 
   X-Linked Recessive Inheritance 27:06 
    Example: Hemophilia, Duchene Muscular Dystrohpy, and Color Blindess 27:07 
   Example 1: Colorblind 29:48 
   Example 2: Pedigree 37:07 
   Example 3: Inheritance Pattern 39:54 
   Example 4: X-inactivation 41:17 
VII. Evolution
  Natural Selection 1:03:28
   Intro 0:00 
   Background 0:09 
    Work of Other Scientists 0:15 
    Aristotle 0:43 
    Carl Linnaeus 1:32 
    George Cuvier 2:47 
    James Hutton 4:10 
    Thomas Malthus 5:05 
    Jean-Baptiste Lamark 5:45 
   Darwin's Theory of Natural Selection 7:50 
    Evolution 8:00 
    Natural Selection 8:43 
    Charles Darwin & The Galapagos Islands 10:20 
   Genetic Variation 20:37 
    Mutations 20:38 
    Independent Assortment 21:04 
    Crossing Over 24:40 
    Random Fertilization 25:26 
   Natural Selection and the Peppered Moth 26:37 
    Natural Selection and the Peppered Moth 26:38 
   Types of Natural Selection 29:52 
    Directional Selection 29:55 
    Stabilizing Selection 32:43 
    Disruptive Selection 34:21 
   Sexual Selection 36:18 
    Sexual Dimorphism 37:30 
    Intersexual Selection 37:57 
    Intrasexual Selection 39:20 
   Evidence for Evolution 40:55 
    Paleontology: Fossil Record 41:30 
    Biogeography 45:35 
    Continental Drift 46:06 
    Pangaea 46:28 
    Marsupials 47:11 
   Homologous and Analogous Structure 50:10 
    Homologous Structure 50:12 
    Analogous Structure 53:21 
   Example 1: Genetic Variation & Natural Selection 56:15 
   Example 2: Types of Natural Selection 58:07 
   Example 3: Mechanisms By Which Genetic Variation is Maintained Within a Population 60:12 
   Example 4: Difference Between Homologous and Analogous Structures 61:28 
  Population Genetic and Evolution 53:22
   Intro 0:00 
   Review of Natural Selection 0:12 
    Review of Natural Selection 0:13 
   Genetic Drift and Gene Flow 4:40 
    Definition of Genetic Drift 4:41 
    Example of Genetic Drift: Cholera Epidemic 5:15 
    Genetic Drift: Founder Effect 7:28 
    Genetic Drift: Bottleneck Effect 10:27 
    Gene Flow 13:00 
   Quantifying Genetic Variation 14:32 
    Average Heterozygosity 15:08 
    Nucleotide Variation 17:05 
   Maintaining Genetic Variation 18:12 
    Heterozygote Advantage 19:45 
    Example of Heterozygote Advantage: Sickle Cell Anemia 20:21 
    Diploidy 23:44 
    Geographic Variation 26:54 
    Frequency Dependent Selection and Outbreeding 28:15 
    Neutral Traits 30:55 
   The Hardy-Weinberg Equilibrium 31:11 
    The Hardy-Weinberg Equilibrium 31:49 
    The Hardy-Weinberg Conditions 32:42 
    The Hardy-Weinberg Equation 34:05 
    The Hardy-Weinberg Example 36:33 
   Example 1: Match Terms to Descriptions 42:28 
   Example 2: The Hardy-Weinberg Equilibrium 44:31 
   Example 3: The Hardy-Weinberg Equilibrium 49:10 
   Example 4: Maintaining Genetic Variation 51:30 
  Speciation and Patterns of Evolution 51:02
   Intro 0:00 
   Early Life on Earth 0:08 
    Early Earth 0:09 
    1920's Oparin & Haldane 0:58 
    Abiogenesis 2:15 
    1950's Miller & Urey 2:45 
    Ribozymes 5:34 
    3.5 Billion Years Ago 6:39 
    2.5 Billion Years Ago 7:14 
    1.5 Billion Years Ago 7:41 
    Endosymbiosis 8:00 
    540 Million Years Ago: Cambrian Explosion 9:57 
   Gradualism and Punctuated Equilibrium 11:46 
    Gradualism 11:47 
    Punctuated Equilibrium 12:45 
   Adaptive Radiation 15:08 
    Adaptive Radiation 15:09 
    Example of Adaptive Radiation: Galapogos Islands 17:11 
   Convergent Evolution, Divergent Evolution, and Coevolution 18:30 
    Convergent Evolution 18:39 
    Divergent Evolution 21:30 
    Coevolution 23:49 
   Speciation 26:27 
    Definition and Example of Species 26:29 
    Reproductive Isolation: Prezygotive 27:49 
    Reproductive Isolation: Post zygotic 29:28 
   Allopatric Speciation 30:21 
    Allopatric Speciation & Geographic Isolation 30:28 
    Genetic Drift 31:31 
   Sympatric Speciation 34:10 
    Sympatric Speciation 34:11 
    Polyploidy & Autopolyploidy 35:12 
    Habitat Isolation 39:17 
    Temporal Isolation 41:27 
    Selection Selection 41:40 
   Example 1: Pattern of Evolution 42:53 
   Example 2: Sympatric Speciation 45:16 
   Example 3: Patterns of Evolution 48:08 
   Example 4: Patterns of Evolution 49:27 
VIII. Diversity of Life
  Classification 1:00:51
   Intro 0:00 
   Systems of Classification 0:07 
    Taxonomy 0:08 
    Phylogeny 1:04 
    Phylogenetics Tree 1:44 
    Cladistics 3:37 
   Classification of Organisms 5:31 
    Example of Carl Linnaeus System 5:32 
   Domains 9:26 
    Kingdoms: Monera, Protista, Plantae, Fungi, Animalia 9:27 
    Monera 10:06 
    Phylogentics Tree: Eurkarya, Bacteria, Archaea 11:58 
    Domain Eukarya 12:50 
   Domain Bacteria 15:43 
    Domain Bacteria 15:46 
    Pathogens 16:41 
    Decomposers 18:00 
   Domain Archaea 19:43 
    Extremophiles Archaea: Thermophiles and Halophiles 19:44 
    Methanogens 20:58 
   Phototrophs, Autotrophs, Chemotrophs and Heterotrophs 24:40 
    Phototrophs and Chemotrophs 25:02 
    Autotrophs and Heterotrophs 26:54 
    Photoautotrophs 28:50 
    Photoheterotrophs 29:28 
    Chemoautotrophs 30:06 
    Chemoheterotrophs 31:37 
   Domain Eukarya 32:40 
    Domain Eukarya 32:43 
    Plant Kingdom 34:28 
    Protists 35:48 
    Fungi Kingdom 37:06 
    Animal Kingdom 38:35 
   Body Symmetry 39:25 
    Lack Symetry 39:40 
    Radial Symmetry: Sea Aneome 40:15 
    Bilateral Symmetry 41:55 
    Cephalization 43:29 
   Germ Layers 44:54 
    Diploblastic Animals 45:18 
    Triploblastic Animals 45:25 
    Ectoderm 45:36 
    Endoderm 46:07 
    Mesoderm 46:41 
   Coelomates 47:14 
    Coelom 47:15 
    Acoelomate 48:22 
    Pseudocoelomate 48:59 
    Coelomate 49:31 
    Protosomes 50:46 
    Deuterosomes 51:20 
   Example 1: Domains 53:01 
   Example 2: Match Terms with Descriptions 56:00 
   Example 3: Kingdom Monera and Domain Archaea 57:50 
   Example 4: System of Classification 59:37 
  Bacteria 36:46
   Intro 0:00 
   Comparison of Domain Archaea and Domain Bacteria 0:08 
    Overview of Archaea and Bacteria 0:09 
    Archaea vs. Bacteria: Nucleus, Organelles, and Organization of Genetic Material 1:45 
    Archaea vs. Bacteria: Cell Walls 2:20 
    Archaea vs. Bacteria: Number of Types of RNA Pol 2:29 
    Archaea vs. Bacteria: Membrane Lipids 2:53 
    Archaea vs. Bacteria: Introns 3:33 
    Bacteria: Pathogen 4:03 
    Bacteria: Decomposers and Fix Nitrogen 5:18 
    Bacteria: Aerobic, Anaerobic, Strict Anaerobes & Facultative Anaerobes 6:02 
   Phototrophs, Autotrophs, Heterotrophs and Chemotrophs 7:14 
    Phototrophs and Chemotrophs 7:50 
    Autotrophs and Heterotrophs 8:53 
    Photoautotrophs and Photoheterotrophs 10:15 
    Chemoautotroph and Chemoheterotrophs 11:07 
   Structure of Bacteria 12:21 
    Shapes: Cocci, Bacilli, Vibrio, and Spirochetes 12:26 
    Structures: Plasma Membrane and Cell Wall 14:23 
    Structures: Nucleoid Region, Plasmid, and Capsule Basal Apparatus, and Filament 15:30 
    Structures: Flagella, Basal Apparatus, Hook, and Filament 16:36 
    Structures: Pili, Fimbrae and Ribosome 18:00 
    Peptidoglycan: Gram + and Gram - 18:50 
   Bacterial Genomes and Reproduction 21:14 
    Bacterial Genomes 21:21 
    Reproduction of Bacteria 22:13 
    Transformation 23:26 
    Vector 24:34 
    Competent 25:15 
   Conjugation 25:53 
    Conjugation: F+ and R Plasmids 25:55 
   Example 1: Species 29:41 
   Example 2: Bacteria and Exchange of Genetic Material 32:31 
   Example 3: Ways in Which Bacteria are Beneficial to Other Organisms 33:48 
   Example 4: Domain Bacteria vs. Domain Archaea 34:53 
  Protists 1:18:48
   Intro 0:00 
   Classification of Protists 0:08 
    Classification of Protists 0:09 
    'Plant-like' Protists 2:06 
    'Animal-like' Protists 3:19 
    'Fungus-like' Protists 3:57 
   Serial Endosymbiosis Theory 5:15 
    Endosymbiosis Theory 5:33 
    Photosynthetic Protists 7:33 
   Life Cycles with a Diploid Adult 13:35 
    Life Cycles with a Diploid Adult 13:56 
   Life Cycles with a Haploid Adult 15:31 
    Life Cycles with a Haploid Adult 15:32 
   Alternation of Generations 17:22 
    Alternation of Generations: Multicellular Haploid & Diploid Phase 17:23 
   Plant-Like Protists 19:58 
    Euglenids 20:43 
    Dino Flagellates 22:57 
    Diatoms 26:07 
   Plant-Like Protists 28:44 
    Golden Algae 28:45 
    Brown Algeas 30:05 
   Plant-Like Protists 33:38 
    Red Algae 33:39 
    Green Algae 35:36 
    Green Algae: Chlamydomonus 37:44 
   Animal-Like Protists 40:04 
    Animal-Like Protists Overview 40:05 
    Sporozoans (Apicomplexans) 40:32 
    Alveolates 41:41 
    Sporozoans (Apicomplexans): Plasmodium & Malaria 42:59 
   Animal-Like Protists 48:44 
    Kinetoplastids 48:50 
    Example of Kinetoplastids: Trypanosomes & African Sleeping Sickness 49:30 
    Ciliate 50:42 
   Conjugation 53:16 
    Conjugation 53:26 
   Animal-Like Protists 57:08 
    Parabasilids 57:31 
    Diplomonads 59:06 
    Rhizopods 60:13 
    Forams 62:25 
    Radiolarians 63:28 
   Fungus-Like Protists 64:25 
    Fungus-Like Protists Overview 64:26 
    Slime Molds 65:15 
    Cellular Slime Molds: Feeding Stage 69:21 
    Oomycetes 71:15 
   Example 1: Alternation of Generations and Sexual Life Cycles 73:05 
   Example 2: Match Protists to Their Descriptions 74:12 
   Example 3: Three Structures that Protists Use for Motility 76:22 
   Example 4: Paramecium 77:04 
  Fungi 35:24
   Intro 0:00 
   Introduction to Fungi 0:09 
    Introduction to Fungi 0:10 
    Mycologist 0:34 
    Examples of Fungi 0:45 
    Hyphae, Mycelia, Chitin, and Coencytic Fungi 2:26 
    Ancestral Protists 5:00 
   Role of Fungi in the Environment 5:35 
    Fungi as Decomposers 5:36 
    Mycorrrhiza 6:19 
    Lichen 8:52 
   Life Cycle of Fungi 11:32 
    Asexual Reproduction 11:33 
    Sexual Reproduction & Dikaryotic Cell 13:16 
   Chytridiomycota 18:12 
    Phylum Chytridiomycota 18:17 
    Zoospores 18:50 
   Zygomycota 19:07 
    Coenocytic & Zygomycota Life Cycle 19:08 
   Basidiomycota 24:27 
    Basidiomycota Overview 24:28 
    Basidiomycota Life Cycle 26:11 
   Ascomycota 28:00 
    Ascomycota Overview 28:01 
    Ascomycota Reproduction 28:50 
   Example 1: Fungi Fill in the Blank 31:02 
   Example 2: Name Two Roles Played by Fungi in the Environment 32:09 
   Example 3: Difference Between Diploid Cell and Dikaryon Cell 33:42 
   Example 4: Phylum of Fungi, Flagellated Spore, Coencytic 34:36 
  Invertebrates 1:03:03
   Intro 0:00 
   Porifera (Sponges) 0:33 
    Chordata 0:56 
    Porifera (Sponges): Sessile, Layers, Aceolomates, and Filter Feeders 1:24 
    Amoebocytes Cell 4:47 
    Choanocytes Cell 5:56 
    Sexual Reproduction 6:28 
   Cnidaria 8:05 
    Cnidaria Overview 8:06 
    Polyp & Medusa: Gastrovasular Cavity 8:29 
    Cnidocytes 9:42 
    Anthozoa 10:40 
    Cubozoa 11:23 
    Hydrozoa 11:53 
    Scyphoza 13:25 
   Platyhelminthes (Flatworms) 13:58 
    Flatworms: Tribloblastic, Bilateral Symmetry, and Cephalization 13:59 
    GI System 15:33 
    Excretory System 16:07 
    Nervous System 17:00 
    Turbellarians 17:36 
    Trematodes 18:42 
    Monageneans 21:32 
    Cestoda 21:55 
   Rotifera (Rotifers) 23:45 
    Rotifers: Digestive Tract, Pseudocoelem, and Stuctures 23:46 
    Reproduction: Parthenogenesis 25:33 
   Nematoda (Roundworms) 26:44 
    Nematoda (Roundworms) 26:45 
    Parasites: Pinworms & Hookworms 27:26 
   Annelida 28:36 
    Annelida Overview 28:37 
    Open Circulatory 29:21 
    Closed Circulatory 30:18 
    Nervous System 31:19 
    Excretory System 31:43 
    Oligochaete 32:07 
    Leeches 33:22 
    Polychaetes 34:42 
   Mollusca 35:26 
    Mollusca Features 35:27 
    Major Part 1: Visceral Mass 36:21 
    Major Part 2: Head-foot Region 36:49 
    Major Part 3: Mantle 37:13 
    Radula 37:49 
    Circulatory, Reproductive, Excretory, and Nervous System 38:14 
   Major Classes of Molluscs 39:12 
    Gastropoda 39:17 
    Polyplacophora 40:15 
    Bivales 40:41 
    Cephalopods 41:42 
   Arthropoda 43:35 
    Arthropoda Overview 43:36 
    Segmented Bodies 44:14 
    Exoskeleton 44:52 
    Jointed Appendages 45:28 
    Hemolyph, Excretory & Respiratory System 45:41 
    Myriapoda & Centipedes 47:15 
    Cheliceriforms 48:20 
    Crustcea 49:31 
    Herapoda 50:03 
   Echinodermata 52:59 
    Echinodermata 53:00 
    Watrer Vascular System 54:20 
   Selected Characteristics of Invertebrates 57:11 
    Selected Characteristics of Invertebrates 57:12 
   Example 1: Phylum Description 58:43 
   Example 2: Complex Animals 59:50 
   Example 3: Match Organisms to the Correct Phylum 61:03 
   Example 4: Phylum Arthropoda 62:01 
  Vertebrates 1:00:07
   Intro 0:00 
   Phylum Chordata 0:06 
    Chordates Overview 0:07 
    Notochord and Dorsal Hollow Nerve Chord 1:24 
    Pharyngeal Clefts, Arches, and Post-anal Tail 3:41 
   Invertebrate Chordates 6:48 
    Lancelets 7:13 
    Tunicates 8:02 
    Hagfishes: Craniates 8:55 
   Vertebrate Chordates 10:41 
    Veterbrates Overview 10:42 
    Lampreys 11:00 
    Gnathostomes 12:20 
    Six Major Classes of Vertebrates 12:53 
   chondrichthyes 14:23 
    Chondrichthyes Overview 14:24 
    Ectothermic and Endothermic 14:42 
    Sharks: Lateral Line System, Neuromastsn, and Gills 15:27 
    Oviparous and Viviparous 17:23 
   Osteichthyes (Bony Fishes) 18:12 
    Osteichythes (Bony Fishes) Overview 18:13 
    Operculum 19:05 
    Swim Bladder 19:53 
    Ray-Finned Fishes 20:34 
    Lobe-Finned Fishes 20:58 
   Tetrapods 22:36 
    Tetrapods: Definition and Examples 22:37 
   Amphibians 23:53 
    Amphibians Overview 23:54 
    Order Urodela 25:51 
    Order Apoda 27:03 
    Order Anura 27:55 
   Reptiles 30:19 
    Reptiles Overview 30:20 
    Amniotes 30:37 
    Examples of Reptiles 32:46 
    Reptiles: Ectotherms, Gas Exchange, and Heart 33:40 
   Orders of Reptiles 34:17 
    Sphenodontia, Squamata, Testudines, and Crocodilia 34:21 
   Birds 36:09 
    Birds and Dinosaurs 36:18 
    Theropods 38:00 
    Birds: High Metabolism, Respiratory System, Lungs, and Heart 39:04 
    Birds: Endothermic, Bones, and Feathers 40:15 
   Mammals 42:33 
    Mammals Overview 42:35 
    Diaphragm and Heart 42:57 
    Diphydont 43:44 
    Synapsids 44:41 
   Monotremes 46:36 
    Monotremes 46:37 
   Marsupials 47:12 
    Marsupials: Definition and Examples 47:16 
    Convergent Evolution 48:09 
   Eutherians (Placental Mammals) 49:42 
    Placenta 49:43 
    Order Carnivora 50:48 
    Order Raodentia 51:00 
    Order Cetaceans 51:14 
   Primates 51:41 
    Primates Overview 51:42 
    Nails and Hands 51:58 
    Vision 52:51 
    Social Care for Young 53:28 
    Brain 53:43 
   Example 1: Distinguishing Characteristics of Chordates 54:33 
   Example 2: Match Description to Correct Term 55:56 
   Example 3: Bird's Anatomy 57:38 
   Example 4: Vertebrate Animal, Marine Environment, and Ectothermic 59:14 
IX. Plants
  Seedless Plants 34:31
   Intro 0:00 
   Origin and Classification of Plants 0:06 
    Origin and Classification of Plants 0:07 
    Non-Vascular vs. Vascular Plants 1:29 
    Seedless Vascular & Seed Plants 2:28 
    Angiosperms & Gymnosperms 2:50 
   Alternation of Generations 3:54 
    Alternation of Generations 3:55 
   Bryophytes 7:58 
    Overview of Bryrophytes 7:59 
    Example: Moss Gametophyte 9:29 
    Example: Moss Sporophyte 9:50 
   Moss Life Cycle 10:12 
    Moss Life Cycle 10:13 
   Seedless Vascular Plants 13:23 
    Vascular Structures: Cell Walls, and Lignin 13:24 
    Homosporous 17:11 
    Heterosporous 17:48 
   Adaptations to Life on land 21:10 
    Adaptation 1: Cell Walls 21:38 
    Adaptation 2: Vascular Plants 21:59 
    Adaptation 3 : Xylem & Phloem 22:31 
    Adaptation 4: Seeds 23:07 
    Adaptation 5: Pollen 23:35 
    Adaptation 6: Stomata 24:45 
    Adaptation 7: Reduced Gametophyte Generation 25:32 
   Example 1: Bryophytes 26:39 
   Example 2: Sporangium, Lignin, Gametophyte, and Antheridium 28:34 
   Example 3: Adaptations to Life on Land 29:47 
   Example 4: Life Cycle of Plant 32:06 
  Plant Structure 1:01:21
   Intro 0:00 
   Plant Tissue 0:05 
    Dermal Tissue 0:15 
    Vascular Tissue 0:39 
    Ground Tissue 1:31 
   Cell Types in Plants 2:14 
    Parenchyma Cells 2:24 
    Collenchyma Cells 3:21 
    Sclerenchyma Cells 3:59 
   Xylem 5:04 
    Xylem: Tracheids and Vessel Elements 6:12 
    Gymnosperms vs. Angiosperms 7:53 
   Phloem 8:37 
    Phloem: Structures and Function 8:38 
    Sieve-Tube Elements 8:45 
    Companion Cells & Sieve Plates 9:11 
   Roots 10:08 
    Taproots & Fibrous 10:09 
    Aerial Roots & Prop Roots 11:41 
    Structures and Functions of Root: Dicot & Monocot 13:00 
    Pericyle 16:57 
   The Nitrogen Cylce 18:05 
    The Nitrogen Cycle 18:06 
   Mycorrhizae 24:20 
    Mycorrhizae 24:23 
    Ectomycorrhiza 26:03 
    Endomycorrhiza 26:25 
   Stems 26:53 
    Stems 26:54 
    Vascular Bundles of Monocots and Dicots 28:18 
   Leaves 29:48 
    Blade & Petiole 30:13 
    Upper Epidermis, Lower Epidermis & Cuticle 30:39 
    Ground Tissue, Palisade Mesophyll, Spongy Mesophyll 31:35 
    Stomata Pores 33:23 
    Guard Cells 34:15 
    Vascular Tissues: Vascular Bundles and Bundle Sheath 34:46 
   Stomata 36:12 
    Stomata & Gas Exchange 36:16 
    Guard Cells, Flaccid, and Turgid 36:43 
    Water Potential 38:03 
    Factors for Opening Stoma 40:35 
    Factors Causing Stoma to Close 42:44 
   Overview of Plant Growth 44:23 
    Overview of Plant Growth 44:24 
   Primary Plant Growth 46:19 
    Apical Meristems 46:25 
    Root Growth: Zone of Cell Division 46:44 
    Root Growth: Zone of Cell Elongation 47:35 
    Root Growth: Zone of Cell Differentiation 47:55 
    Stem Growth: Leaf Primodia 48:16 
   Secondary Plant Growth 48:48 
    Secondary Plant Growth Overview 48:59 
    Vascular Cambium: Secondary Xylem and Phloem 49:38 
    Cork Cambium: Periderm and Lenticels 51:10 
   Example 1: Leaf Structures 53:30 
   Example 2: List Three Types of Plant Tissue and their Major Functions 55:13 
   Example 3: What are Two Factors that Stimulate the Opening or Closing of Stomata? 56:58 
   Example 4: Plant Growth 59:18 
  Gymnosperms and Angiosperms 1:01:51
   Intro 0:00 
   Seed Plants 0:22 
    Sporopollenin 0:58 
    Heterosporous: Megasporangia 2:49 
    Heterosporous: Microsporangia 3:19 
   Gymnosperms 5:20 
    Gymnosperms 5:21 
   Gymnosperm Life Cycle 7:30 
    Gymnosperm Life Cycle 7:31 
   Flower Structure 15:15 
    Petal & Pollination 15:48 
    Sepal 16:52 
    Stamen: Anther, Filament 17:05 
    Pistill: Stigma, Style, Ovule, Ovary 17:55 
    Complete Flowers 20:14 
   Angiosperm Gametophyte Formation 20:47 
    Male Gametophyte: Microsporocytes, Microsporangia & Meiosis 20:57 
    Female Gametophyte: Megasporocytes & Meiosis 24:22 
   Double Fertilization 25:43 
    Double Fertilization: Pollen Tube and Endosperm 25:44 
   Angiosperm Life Cycle 29:43 
    Angiosperm Life Cycle 29:48 
   Seed Structure and Development 33:37 
    Seed Structure and Development 33:38 
   Pollen Dispersal 37:53 
    Abiotic 38:28 
    Biotic 39:30 
   Prevention of Self-Pollination 40:48 
    Mechanism 1 41:08 
    Mechanism 2: Dioecious 41:37 
    Mechanism 3 42:32 
    Self-Incompatibility 43:08 
    Gametophytic Self-Incompatibility 44:38 
    Sporophytic Self-Incompatibility 46:50 
   Asexual Reproduction 48:33 
    Asexual Reproduction & Vegetative Propagation 48:34 
    Graftiry 50:19 
   Monocots and Dicots 51:34 
    Monocots vs.Dicots 51:35 
   Example 1: Double Fertilization 54:43 
   Example 2: Mechanisms of Self-Fertilization 56:02 
   Example 3: Monocots vs. Dicots 58:11 
   Example 4: Flower Structures 60:11 
  Transport of Nutrients and Water in Plants 40:30
   Intro 0:00 
   Review of Plant Cell Structure 0:14 
    Cell Wall, Plasma Membrane, Middle lamella, and Cytoplasm 0:15 
    Plasmodesmata, Chloroplasts, and Central Vacuole 3:24 
   Water Absorption by Plants 4:28 
    Root Hairs and Mycorrhizae 4:30 
    Osmosis and Water Potential 5:41 
   Apoplast and Symplast Pathways 10:01 
    Apoplast and Symplast Pathways 10:02 
   Xylem Structure 21:02 
    Tracheids and Vessel Elements 21:03 
   Bulk Flow 23:00 
    Transpiration 23:26 
    Cohesion 25:10 
    Adhesion 26:10 
   Phloem Structure 27:25 
    Pholem 27:26 
    Sieve-Tube Elements 27:48 
    Companion Cells 28:17 
   Translocation 28:42 
    Sugar Source and Sugar Sink Overview 28:43 
    Example of Sugar Sink 30:01 
    Example of Sugar Source 30:48 
   Example 1: Match the Following Terms to their Description 33:17 
   Example 2: Water Potential 34:58 
   Example 3: Bulk Flow 36:56 
   Example 4: Sugar Sink and Sugar Source 38:33 
  Plant Hormones and Tropisms 48:10
   Intro 0:00 
   Plant Cell Signaling 0:17 
    Plant Cell Signaling Overview 0:18 
    Step 1: Reception 1:03 
    Step 2: Transduction 2:32 
    Step 3: Response 2:58 
    Second Messengers 3:52 
    Protein Kinases 4:42 
   Auxins 6:14 
    Auxins 6:18 
    Indoleacetic Acid (IAA) 7:23 
   Cytokinins and Gibberellins 11:10 
    Cytokinins: Apical Dominance & Delay of Aging 11:16 
    Gibberellins: 'Bolting' 13:51 
   Ethylene 15:33 
    Ethylene 15:34 
    Positive Feedback 15:46 
    Leaf Abscission 18:05 
    Mechanical Stress: Triple Response 19:36 
   Abscisic Acid 21:10 
    Abscisic Acid 21:15 
   Tropisms 23:11 
    Positive Tropism 23:50 
    Negative Tropism 24:07 
    Statoliths 26:21 
   Phytochromes and Photoperiodism 27:48 
    Phytochromes: PR and PFR 27:56 
    Circadian Rhythms 32:06 
    Photoperiod 33:13 
    Photoperiodism 33:38 
    Gerner & Allard 34:35 
    Short-Day Plant 35:22 
    Long-Day Plant 37:00 
   Example 1: Plant Hormones 41:28 
   Example 2: Cytokinins & Gibberellins 43:00 
   Example 3: Match the Following Terms to their Description 44:46 
   Example 4: Hormones & Cell Response 46:14 
X. Animal Structure and Physiology
  The Respiratory System 48:14
   Intro 0:00 
   Gas Exchange in Animals 0:17 
    Respiration 0:19 
    Ventilation 1:09 
    Characteristics of Respiratory Surfaces 1:53 
   Gas Exchange in Aquatic Animals 3:05 
    Simple Aquatic Animals 3:06 
    Gills & Gas Exchange in Complex Aquatic Animals 3:49 
    Countercurrent Exchange 6:12 
   Gas Exchange in Terrestrial Animals 13:46 
    Earthworms 14:07 
    Internal Respiratory 15:35 
    Insects 16:55 
    Circulatory Fluid 19:06 
   The Human Respiratory System 21:21 
    Nasal Cavity, Pharynx, Larynx, and Epiglottis 21:50 
    Bronchus, Bronchiole, Trachea, and Alveoli 23:38 
    Pulmonary Surfactants 28:05 
    Circulatory System: Hemoglobin 29:13 
   Ventilation 30:28 
    Inspiration/Expiration: Diaphragm, Thorax, and Abdomen 30:33 
    Breathing Control Center: Regulation of pH 34:34 
   Example 1: Tracheal System in Insects 39:08 
   Example 2: Countercurrent Exchange 42:09 
   Example 3: Respiratory System 44:10 
   Example 4: Diaphragm, Ventilation, pH, and Regulation of Breathing 45:31 
  The Circulatory System 1:20:21
   Intro 0:00 
   Types of Circulatory Systems 0:07 
    Circulatory System Overview 0:08 
    Open Circulatory System 3:19 
    Closed Circulatory System 5:58 
   Blood Vessels 7:51 
    Arteries 8:16 
    Veins 10:01 
    Capillaries 12:35 
   Vasoconstriction and Vasodilation 13:10 
    Vasoconstriction 13:11 
    Vasodilation 13:47 
    Thermoregulation 14:32 
   Blood 15:53 
    Plasma 15:54 
    Cellular Component: Red Blood Cells 17:41 
    Cellular Component: White Blood Cells 20:18 
    Platelets 21:14 
    Blood Types 21:35 
   Clotting 27:04 
    Blood, Fibrin, and Clotting 27:05 
    Hemophilia 30:26 
   The Heart 31:09 
    Structures and Functions of the Heart 31:19 
   Pulmonary and Systemic Circulation 40:20 
    Double Circuit: Pulmonary Circuit and Systemic Circuit 40:21 
   The Cardiac Cycle 42:35 
    The Cardiac Cycle 42:36 
    Autonomic Nervous System 50:00 
   Hemoglobin 51:25 
    Hemoglobin & Hemocyanin 51:26 
   Oxygen-Hemoglobin Dissociation Curve 55:30 
    Oxygen-Hemoglobin Dissociation Curve 55:44 
   Transport of Carbon Dioxide 66:31 
    Transport of Carbon Dioxide 66:37 
   Example 1: Pathway of Blood 72:48 
   Example 2: Oxygenated Blood, Pacemaker, and Clotting 75:24 
   Example 3: Vasodilation and Vasoconstriction 76:19 
   Example 4: Oxygen-Hemoglobin Dissociation Curve 78:13 
  The Digestive System 56:11
   Intro 0:00 
   Introduction to Digestion 0:07 
    Digestive Process 0:08 
    Intracellular Digestion 0:45 
    Extracellular Digestion 1:44 
   Types of Digestive Tracts 2:08 
    Gastrovascular Cavity 2:09 
    Complete Gastrointestinal Tract (Alimentary Canal) 3:54 
    'Crop' 4:43 
   The Human Digestive System 5:41 
    Structures of the Human Digestive System 5:47 
   The Oral Cavity and Esophagus 7:47 
    Mechanical & Chemical Digestion 7:48 
    Salivary Glands 8:55 
    Pharynx and Epigloltis 9:43 
    Peristalsis 11:35 
   The Stomach 12:57 
    Lower Esophageal Sphincter 13:00 
    Gastric Gland, Parietal Cells, and Pepsin 14:32 
    Mucus Cell 15:48 
    Chyme & Pyloric Sphincter 17:32 
   The Pancreas 18:31 
    Endocrine and Exocrine 19:03 
    Amylase 20:05 
    Proteases 20:51 
    Lipases 22:20 
   The Liver 23:08 
    The Liver & Production of Bile 23:09 
   The Small Intestine 24:37 
    The Small Intestine 24:38 
    Duodenum 27:44 
    Intestinal Enzymes 28:41 
   Digestive Enzyme 33:30 
    Site of Production: Mouth 33:43 
    Site of Production: Stomach 34:03 
    Site of Production: Pancreas 34:16 
    Site of Production: Small Intestine 36:18 
   Absorption of Nutrients 37:51 
    Absorption of Nutrients: Jejunum and Ileum 37:52 
   The Large Intestine 44:52 
    The Large Intestine: Colon, Cecum, and Rectum 44:53 
   Regulation of Digestion by Hormones 46:55 
    Gastrin 47:21 
    Secretin 47:50 
    Cholecystokinin (CCK) 48:00 
   Example 1: Intestinal Cell, Bile, and Digestion of Fats 48:29 
   Example 2: Matching 51:06 
   Example 3: Digestion and Absorption of Starch 52:18 
   Example 4: Large Intestine and Gastric Fluids 54:52 
  The Excretory System 1:12:14
   Intro 0:00 
   Nitrogenous Wastes 0:08 
    Nitrogenous Wastes Overview 0:09 
    NH3 0:39 
    Urea 2:43 
    Uric Acid 3:31 
   Osmoregulation 4:56 
    Osmoregulation 5:05 
    Saltwater Fish vs. Freshwater Fish 8:58 
   Types of Excretory Systems 13:42 
    Protonephridia 13:50 
    Metanephridia 16:15 
    Malpighian Tubule 19:05 
   The Human Excretory System 20:45 
    Kidney, Ureter, bladder, Urethra, Medula, and Cortex 20:53 
   Filtration, Reabsorption and Secretion 22:53 
    Filtration 22:54 
    Reabsorption 24:16 
    Secretion 25:20 
   The Nephron 26:23 
    The Nephron 26:24 
   The Nephron, cont. 41:45 
    Descending Loop of Henle 41:46 
    Ascending Loop of Henle 45:45 
   Antidiuretic Hormone 54:30 
    Antidiuretic Hormone (ADH) 54:31 
   Aldosterone 58:58 
    Aldosterone 58:59 
   Example 1: Nephron of an Aquatic Mammal 64:21 
   Example 2: Uric Acid & Saltwater Fish 66:36 
   Example 3: Nephron 69:14 
   Example 4: Gastrointestinal Infection 70:41 
  The Endocrine System 51:12
   Intro 0:00 
   The Endocrine System Overview 0:07 
    Thyroid 0:08 
    Exocrine 1:56 
    Pancreas 2:44 
    Paracrine Signaling 4:06 
    Pheromones 5:15 
   Mechanisms of Hormone Action 6:06 
    Reception, Transduction, and Response 7:06 
    Classes of Hormone 10:05 
    Negative Feedback: Testosterone Example 12:16 
   The Pancreas 15:11 
    The Pancreas & islets of Langerhan 15:12 
    Insulin 16:02 
    Glucagon 17:28 
   The Anterior Pituitary 19:25 
    Thyroid Stimulating Hormone 20:24 
    Adrenocorticotropic Hormone 21:16 
    Follide Stimulating Hormone 22:04 
    Luteinizing Hormone 22:45 
    Growth Hormone 23:45 
    Prolactin 24:24 
    Melanocyte Stimulating Hormone 24:55 
   The Hypothalamus and Posterior Pituitary 25:45 
    Hypothalamus, Oxytocin, Antidiuretic Hormone (ADH), and Posterior Pituitary 25:46 
   The Adrenal Glands 31:20 
    Adrenal Cortex 31:56 
    Adrenal Medulla 34:29 
   The Thyroid 35:54 
    Thyroxine 36:09 
    Calcitonin 40:27 
   The Parathyroids 41:44 
    Parathyroids Hormone (PTH) 41:45 
   The Ovaries and Testes 43:32 
    Estrogen, Progesterone, and Testosterone 43:33 
   Example 1: Match the Following Hormones with their Descriptions 45:38 
   Example 2: Pancreas, Endocrine Organ & Exocrine Organ 47:06 
   Example 3: Insulin and Glucagon 48:28 
   Example 4: Increased Level of Cortisol in Blood 50:25 
  The Nervous System 1:10:38
   Intro 0:00 
   Types of Nervous Systems 0:28 
    Nerve Net 0:37 
    Flatworm 1:07 
    Cephalization 1:52 
    Arthropods 2:44 
    Echinoderms 3:11 
   Nervous System Organization 3:40 
    Nervous System Organization Overview 3:41 
    Automatic Nervous System: Sympathetic & Parasympathetic 4:42 
   Neuron Structure 6:57 
    Cell Body & Dendrites 7:16 
    Axon & Axon Hillock 8:20 
    Synaptic Terminals, Mylenin, and Nodes of Ranvier 9:01 
   Pre-synaptic and Post-synaptic Cells 10:16 
    Pre-synaptic Cells 10:17 
    Post-synaptic Cells 11:05 
   Types of Neurons 11:50 
    Sensory Neurons 11:54 
    Motor Neurons 13:12 
    Interneurons 14:24 
   Resting Potential 15:14 
    Membrane Potential 15:25 
    Resting Potential: Chemical Gradient 16:06 
    Resting Potential: Electrical Gradient 19:18 
   Gated Ion Channels 24:40 
    Voltage-Gated & Ligand-Gated Ion Channels 24:48 
   Action Potential 30:09 
    Action Potential Overview 30:10 
    Step 1 32:07 
    Step 2 32:17 
    Step 3 33:12 
    Step 4 35:14 
    Step 5 36:39 
   Action Potential Transmission 39:04 
    Action Potential Transmission 39:05 
    Speed of Conduction 41:19 
    Saltatory Conduction 42:58 
   The Synapse 44:17 
    The Synapse: Presynaptic & Postsynaptic Cell 44:31 
    Examples of Neurotransmitters 50:05 
   Brain Structure 51:57 
    Meniges 52:19 
    Cerebrum 52:56 
    Corpus Callosum 53:13 
    Gray & White Matter 53:38 
    Cerebral Lobes 55:35 
    Cerebellum 56:00 
    Brainstem 56:30 
    Medulla 56:51 
    Pons 57:22 
    Midbrain 57:55 
    Thalamus 58:25 
    Hypothalamus 58:58 
    Ventricles 59:51 
   The Spinal Cord 60:29 
    Sensory Stimuli 60:30 
    Reflex Arc 61:41 
   Example 1: Automatic Nervous System 64:38 
   Example 2: Synaptic Terminal and the Release of Neurotransmitters 66:22 
   Example 3: Volted-Gated Ion Channels 68:00 
   Example 4: Neuron Structure 69:26 
  Musculoskeletal System 39:29
   Intro 0:00 
   Skeletal System Types and Function 0:30 
    Skeletal System 0:31 
    Exoskeleton 1:34 
    Endoskeleton 2:32 
   Skeletal System Components 2:55 
    Bone 3:06 
    Cartilage 5:04 
    Tendons 6:18 
    Ligaments 6:34 
   Skeletal Muscle 6:52 
    Skeletal Muscle 7:24 
    Sarcomere 9:50 
   The Sliding Filament Theory 13:12 
    The Sliding Filament Theory: Muscle Contraction 13:13 
   The Neuromuscular Junction 17:24 
    The Neuromuscular Junction: Motor Neuron & Muscle Fiber 17:26 
    Sarcolemma, Sarcoplasmic 21:54 
    Tropomyosin & Troponin 23:35 
   Summation and Tetanus 25:26 
    Single Twitch, Summation of Two Twitches, and Tetanus 25:27 
   Smooth Muscle 28:50 
    Smooth Muscle 28:58 
   Cardiac Muscle 30:40 
    Cardiac Muscle 30:42 
   Summary of Muscle Types 32:07 
    Summary of Muscle Types 32:08 
   Example 1: Contraction and Skeletal Muscle 33:15 
   Example 2: Skeletal Muscle and Smooth Muscle 36:23 
   Example 3: Muscle Contraction, Bone, and Nonvascularized Connective Tissue 37:31 
   Example 4: Sarcomere 38:17 
  The Immune System 1:24:28
   Intro 0:00 
   The Lymphatic System 0:16 
    The Lymphatic System Overview 0:17 
    Function 1 1:23 
    Function 2 2:27 
   Barrier Defenses 3:41 
    Nonspecific vs. Specific Immune Defenses 3:42 
    Barrier Defenses 5:12 
   Nonspecific Cellular Defenses 7:50 
    Nonspecific Cellular Defenses Overview 7:53 
    Phagocytes 9:29 
    Neutrophils 11:43 
    Macrophages 12:15 
    Natural Killer Cells 12:55 
    Inflammatory Response 14:19 
    Complement 18:16 
    Interferons 18:40 
   Specific Defenses - Acquired Immunity 20:12 
    T lymphocytes and B lymphocytes 20:13 
   B Cells 23:35 
    B Cells & Humoral Immunity 23:41 
   Clonal Selection 29:50 
    Clonal Selection 29:51 
    Primary Immune Response 34:28 
    Secondary Immune Response 35:31 
    Cytotoxic T Cells 38:41 
    Helper T Cells 39:20 
   Major Histocompatibility Complex Molecules 40:44 
    Major Histocompatibility Complex Molecules 40:55 
   Helper T Cells 52:36 
    Helper T Cells 52:37 
   Mechanisms of Antibody Action 59:00 
    Mechanisms of Antibody Action 59:01 
    Opsonization 60:01 
    Complement System 61:57 
   Classes of Antibodies 62:45 
    IgM 63:01 
    IgA 63:17 
    IgG 63:53 
    IgE 64:10 
   Passive and Active Immunity 65:00 
    Passive Immunity 65:01 
    Active Immunity 67:49 
   Recognition of Self and Non-Self 69:32 
    Recognition of Self and Non-Self 69:33 
    Self-Tolerance & Autoimmune Diseases 70:50 
   Immunodeficiency 73:27 
    Immunodeficiency 73:28 
    Chemotherapy 73:56 
    AID 74:27 
   Example 1: Match the Following Terms with their Descriptions 75:26 
   Example 2: Three Components of Non-specific Immunity 77:59 
   Example 3: Immunodeficient 81:19 
   Example 4: Self-tolerance and Autoimmune Diseases 83:07 
XI. Animal Reproduction and Development
  Reproduction 1:01:41
   Intro 0:00 
   Asexual Reproduction 0:17 
    Fragmentation 0:53 
    Fission 1:54 
    Parthenogenesis 2:38 
   Sexual Reproduction 4:00 
    Sexual Reproduction 4:01 
    Hermaphrodite 8:08 
   The Male Reproduction System 8:54 
    Seminiferous Tubules & Leydig Cells 8:55 
    Epididymis 9:48 
    Seminal Vesicle 11:19 
    Bulbourethral 12:37 
   The Female Reproductive System 13:25 
    Ovaries 13:28 
    Fallopian 14:50 
    Endometrium, Uterus, Cilia, and Cervix 15:03 
    Mammary Glands 16:44 
   Spermatogenesis 17:08 
    Spermatogenesis 17:09 
   Oogenesis 21:01 
    Oogenesis 21:02 
   The Menstrual Cycle 27:56 
    The Menstrual Cycle: Ovarian and Uterine Cycle 27:57 
   Summary of the Ovarian and Uterine Cycles 42:54 
    Ovarian 42:55 
    Uterine 44:51 
   Oxytocin and Prolactin 46:33 
    Oxytocin 46:34 
    Prolactin 47:00 
   Regulation of the Male Reproductive System 47:28 
    Hormones: GnRH, LH, FSH, and Testosterone 47:29 
   Fertilization 50:11 
    Fertilization 50:12 
    Structures of Egg 50:28 
    Acrosomal Reaction 51:36 
    Cortical Reaction 53:09 
   Example 1: List Three Differences between Spermatogenesis and oogenesis 55:36 
   Example 2: Match the Following Terms to their Descriptions 57:34 
   Example 3: Pregnancy and the Ovarian Cycle 58:44 
   Example 4: Hormone 60:43 
  Development 50:05
   Intro 0:00 
   Cleavage 0:31 
    Cleavage 0:32 
    Meroblastic 2:06 
    Holoblastic Cleavage 3:23 
    Protostomes 4:34 
    Deuterostomes 5:13 
    Totipotent 5:52 
   Blastula Formation 6:42 
    Blastula 6:46 
   Gastrula Formation 8:12 
    Deuterostomes 11:02 
    Protostome 11:44 
    Ectoderm 12:17 
    Mesoderm 12:55 
    Endoderm 13:40 
   Cytoplasmic Determinants 15:19 
    Cytoplasmic Determinants 15:23 
   The Bird Embryo 22:52 
    Cleavage 23:35 
    Blastoderm 23:55 
    Primitive Streak 25:38 
    Migration and Differentiation 27:09 
   Extraembryonic Membranes 28:33 
    Extraembryonic Membranes 28:34 
    Chorion 30:02 
    Yolk Sac 30:36 
    Allantois 31:04 
   The Mammalian Embryo 32:18 
    Cleavage 32:28 
    Blastocyst 32:44 
    Trophoblast 34:37 
    Following Implantation 35:48 
   Organogenesis 37:04 
    Organogenesis, Notochord and Neural Tube 37:05 
   Induction 40:15 
    Induction 40:39 
    Fate Mapping 41:40 
   Example 1: Processes and Stages of Embryological Development 42:49 
   Example 2: Transplanted Cells 44:33 
   Example 3: Germ Layer 46:41 
   Example 4: Extraembryonic Membranes 47:28 
XII. Animal Behavior
  Animal Behavior 47:48
   Intro 0:00 
   Introduction to Animal Behavior 0:05 
    Introduction to Animal Behavior 0:06 
    Ethology 1:04 
    Proximate Cause & Ultimate Cause 1:46 
   Fixed Action Pattern 3:07 
    Sign Stimulus 3:40 
    Releases and Example 3:55 
    Exploitation and Example 7:23 
   Learning 8:56 
    Habituation, Associative Learning, and Imprinting 8:57 
   Habituation 10:03 
    Habituation: Definition and Example 10:04 
   Associative Learning 11:47 
    Classical 12:19 
    Operant Conditioning 13:40 
    Positive & Negative Reinforcement 14:59 
    Positive & Negative Punishment 16:13 
    Extinction 17:28 
   Imprinting 17:47 
    Imprinting: Definition and Example 17:48 
   Social Behavior 20:12 
    Cooperation 20:38 
    Agonistic 21:37 
    Dorminance Heirarchies 23:23 
    Territoriality 24:08 
    Altruism 24:55 
   Communication 26:56 
    Communication 26:57 
   Mating 32:38 
    Mating Overview 32:40 
    Promiscuous 33:13 
    Monogamous 33:32 
    Polygamous 33:48 
    Intrasexual 34:22 
    Intersexual Selection 35:08 
   Foraging 36:08 
    Optimal Foraging Model 36:39 
    Foraging 37:47 
   Movement 39:12 
    Kinesis 39:20 
    Taxis 40:17 
    Migration 40:54 
   Lunar Cycles 42:02 
    Lunar Cycles 42:08 
   Example 1: Types of Conditioning 43:19 
   Example 2: Match the Following Terms to their Descriptions 44:12 
   Example 3: How is the Optimal Foraging Model Used to Explain Foraging Behavior 45:47 
   Example 4: Learning 46:54 
XIII. Ecology
  Biomes 58:49
   Intro 0:00 
   Ecology 0:08 
    Ecology 0:14 
    Environment 0:22 
    Integrates 1:41 
    Environment Impacts 2:20 
   Population and Distribution 3:20 
    Population 3:21 
    Range 4:50 
    Potential Range 5:10 
    Abiotic 5:46 
    Biotic 6:22 
   Climate 7:55 
    Temperature 8:40 
    Precipitation 10:00 
    Wind 10:37 
    Sunlight 10:54 
    Macroclimates & Microclimates 11:31 
   Other Abiotic Factors 12:20 
    Geography 12:28 
    Water 13:17 
    Soil and Rocks 13:48 
   Sunlight 14:42 
    Sunlight 14:43 
   Seasons 15:43 
    June Solstice, December Solstice, March Equinox, and September Equinox 15:44 
    Tropics 19:00 
    Seasonability 19:39 
   Wind and Weather Patterns 20:44 
    Vertical Circulation 20:51 
    Surface Wind Patterns 25:18 
   Local Climate Effects 26:51 
    Local Climate Effects 26:52 
   Terrestrial Biomes 30:04 
    Biome 30:05 
    Forest 31:02 
   Tropical Forest 32:00 
    Tropical Forest 32:01 
   Temperate Broadleaf Forest 32:55 
    Temperate Broadleaf Forest 32:56 
   Coniferous/Taiga Forest 34:10 
    Coniferous/Taiga Forest 34:11 
   Desert 36:05 
    Desert 36:06 
   Grassland 37:45 
    Grassland 37:46 
   Tundra 40:09 
    Tundra 40:10 
   Freshwater Biomes 42:25 
    Freshwater Biomes: Zones 42:27 
    Eutrophic Lakes 44:24 
    Oligotrophic Lakes 45:01 
    Lakes Turnover 46:03 
    Rivers 46:51 
    Wetlands 47:40 
    Estuary 48:11 
   Marine Biomes 48:45 
    Marine Biomes: Zones 48:46 
   Example 1: Diversity of Life 52:18 
   Example 2: Marine Biome 53:08 
   Example 3: Season 54:20 
   Example 4: Biotic vs. Abiotic 55:54 
  Population 41:16
   Intro 0:00 
   Population 0:07 
    Size 'N' 0:16 
    Density 0:41 
    Dispersion 1:01 
    Measure Population: Count Individuals, Sampling, and Proxymeasure 2:26 
   Mortality 7:29 
    Mortality and Survivorship 7:30 
   Age Structure Diagrams 11:52 
    Expanding with Rapid Growth, Expanding, and Stable 11:58 
   Population Growth 15:39 
    Biotic Potential & Exponential Growth 15:43 
   Logistic Population Growth 19:07 
    Carrying Capacity (K) 19:18 
    Limiting Factors 20:55 
   Logistic Model and Oscillation 22:55 
    Logistic Model and Oscillation 22:56 
   Changes to the Carrying Capacity 24:36 
    Changes to the Carrying Capacity 24:37 
   Growth Strategies 26:07 
    'r-selected' or 'r-strategist' 26:23 
    'K-selected' or 'K-strategist' 27:47 
   Human Population 30:15 
    Human Population and Exponential Growth 30:21 
   Case Study - Lynx and Hare 31:54 
    Case Study - Lynx and Hare 31:55 
   Example 1: Estimating Population Size 34:35 
   Example 2: Population Growth 36:45 
   Example 3: Carrying Capacity 38:17 
   Example 4: Types of Dispersion 40:15 
  Communities 1:06:26
   Intro 0:00 
   Community 0:07 
    Ecosystem 0:40 
    Interspecific Interactions 1:14 
   Competition 2:45 
    Competition Overview 2:46 
    Competitive Exclusion 3:57 
    Resource Partitioning 4:45 
    Character Displacement 6:22 
   Predation 7:46 
    Predation 7:47 
    True Predation 8:05 
    Grazing/ Herbivory 8:39 
   Predator Adaptation 10:13 
    Predator Strategies 10:22 
    Physical Features 11:02 
   Prey Adaptation 12:14 
    Prey Adaptation 12:23 
    Aposematic Coloration 13:35 
    Batesian Mimicry 14:32 
    Size 15:42 
   Parasitism 16:48 
    Symbiotic Relationship 16:54 
    Ectoparasites 18:31 
    Endoparasites 18:53 
    Hyperparisitism 19:21 
    Vector 20:08 
    Parasitoids 20:54 
   Mutualism 21:23 
    Resource - Resource mutualism 21:34 
    Service - Resource Mutualism 23:31 
    Service - Service Mutualism: Obligate & Facultative 24:23 
   Commensalism 26:01 
    Commensalism 26:03 
    Symbiosis 27:31 
   Trophic Structure 28:35 
    Producers & Consumers: Autotrophs & Heterotrophs 28:36 
   Food Chain 33:26 
    Producer & Consumers 33:38 
   Food Web 39:01 
    Food Web 39:06 
   Significant Species within Communities 41:42 
    Dominant Species 41:50 
    Keystone Species 42:44 
    Foundation Species 43:41 
   Community Dynamics and Disturbances 44:31 
    Disturbances 44:33 
    Duration 47:01 
    Areal Coverage 47:22 
    Frequency 47:48 
    Intensity 48:04 
    Intermediate Level of Disturbance 48:20 
   Ecological Succession 50:29 
    Primary and Secondary Ecological Succession 50:30 
   Example 1: Competition Situation & Outcome 57:18 
   Example 2: Food Chains 60:08 
   Example 3: Ecological Units 62:44 
   Example 4: Disturbances & Returning to the Original Climax Community 64:30 
  Energy and Ecosystems 57:42
   Intro 0:00 
   Ecosystem: Biotic & Abiotic Components 0:15 
    First Law of Thermodynamics & Energy Flow 0:40 
    Gross Primary Productivity (GPP) 3:52 
    Net Primary Productivity (NPP) 4:50 
   Biogeochemical Cycles 7:16 
    Law of Conservation of Mass & Biogeochemical Cycles 7:17 
   Water Cycle 10:55 
    Water Cycle 10:57 
   Carbon Cycle 17:52 
    Carbon Cycle 17:53 
   Nitrogen Cycle 22:40 
    Nitrogen Cycle 22:41 
   Phosphorous Cycle 29:34 
    Phosphorous Cycle 29:35 
   Climate Change 33:20 
    Climate Change 33:21 
   Eutrophication 39:38 
    Nitrogen 40:34 
    Phosphorous 41:29 
    Eutrophication 42:55 
   Example 1: Energy and Ecosystems 45:28 
   Example 2: Atmospheric CO2 48:44 
   Example 3: Nitrogen Cycle 51:22 
   Example 4: Conversion of a Forest near a Lake to Farmland 53:20 
XIV. Laboratory Review
  Laboratory Review 2:04:30
   Intro 0:00 
   Lab 1: Diffusion and Osmosis 0:09 
    Lab 1: Diffusion and Osmosis 0:10 
   Lab 1: Water Potential 11:55 
    Lab 1: Water Potential 11:56 
   Lab 2: Enzyme Catalysis 18:30 
    Lab 2: Enzyme Catalysis 18:31 
   Lab 3: Mitosis and Meiosis 27:40 
    Lab 3: Mitosis and Meiosis 27:41 
   Lab 3: Mitosis and Meiosis 31:50 
    Ascomycota Life Cycle 31:51 
   Lab 4: Plant Pigments and Photosynthesis 40:36 
    Lab 4: Plant Pigments and Photosynthesis 40:37 
   Lab 5: Cell Respiration 49:56 
    Lab 5: Cell Respiration 49:57 
   Lab 6: Molecular Biology 55:06 
    Lab 6: Molecular Biology & Transformation 1st Part 55:07 
   Lab 6: Molecular Biology 61:16 
    Lab 6: Molecular Biology 2nd Part 61:17 
   Lab 7: Genetics of Organisms 67:32 
    Lab 7: Genetics of Organisms 67:33 
   Lab 7: Chi-square Analysis 73:00 
    Lab 7: Chi-square Analysis 73:03 
   Lab 8: Population Genetics and Evolution 80:41 
    Lab 8: Population Genetics and Evolution 80:42 
   Lab 9: Transpiration 84:02 
    Lab 9: Transpiration 84:03 
   Lab 10: Physiology of the Circulatory System 91:05 
    Lab 10: Physiology of the Circulatory System 91:06 
   Lab 10: Temperature and Metabolism in Ectotherms 98:25 
    Lab 10: Temperature and Metabolism in Ectotherms 98:30 
   Lab 11: Animal Behavior 100:52 
    Lab 11: Animal Behavior 100:53 
   Lab 12: Dissolved Oxygen & Aquatic Primary Productivity 105:36 
    Lab 12: Dissolved Oxygen & Aquatic Primary Productivity 105:37 
   Lab 12: Primary Productivity 109:06 
    Lab 12: Primary Productivity 109:07 
   Example 1: Chi-square Analysis 116:31 
   Example 2: Mitosis 119:28 
   Example 3: Transpiration of Plants 120:27 
   Example 4: Population Genetic 121:16 
XV. The AP Biology Test
  Understanding the Basics 13:02
   Intro 0:00 
   AP Biology Structure 0:18 
    Section I 0:31 
    Section II 1:16 
   Scoring 2:04 
   The Four 'Big Ideas' 3:51 
    Process of Evolution 4:37 
    Biological Systems Utilize 4:44 
    Living Systems 4:55 
    Biological Systems Interact 5:03 
   Items to Bring to the Test 7:56 
   Test Taking Tips 9:53 
XVI. Practice Test (Barron's 4th Edition)
  AP Biology Practice Exam: Section I, Part A, Multiple Choice Questions 1-31 1:04:29
   Intro 0:00 
   AP Biology Practice Exam 0:14 
   Multiple Choice 1 0:40 
   Multiple Choice 2 2:27 
   Multiple Choice 3 4:30 
   Multiple Choice 4 6:43 
   Multiple Choice 5 9:27 
   Multiple Choice 6 11:32 
   Multiple Choice 7 12:54 
   Multiple Choice 8 14:42 
   Multiple Choice 9 17:06 
   Multiple Choice 10 18:42 
   Multiple Choice 11 20:49 
   Multiple Choice 12 23:23 
   Multiple Choice 13 26:20 
   Multiple Choice 14 27:52 
   Multiple Choice 15 28:44 
   Multiple Choice 16 33:07 
   Multiple Choice 17 35:31 
   Multiple Choice 18 39:43 
   Multiple Choice 19 40:37 
   Multiple Choice 20 42:47 
   Multiple Choice 21 45:58 
   Multiple Choice 22 49:49 
   Multiple Choice 23 53:44 
   Multiple Choice 24 55:12 
   Multiple Choice 25 55:59 
   Multiple Choice 26 56:50 
   Multiple Choice 27 58:08 
   Multiple Choice 28 59:54 
   Multiple Choice 29 61:36 
   Multiple Choice 30 62:31 
   Multiple Choice 31 63:50 
  AP Biology Practice Exam: Section I, Part A, Multiple Choice Questions 32-63 50:44
   Intro 0:00 
   AP Biology Practice Exam 0:14 
   Multiple Choice 32 0:27 
   Multiple Choice 33 4:14 
   Multiple Choice 34 5:12 
   Multiple Choice 35 6:51 
   Multiple Choice 36 10:46 
   Multiple Choice 37 11:27 
   Multiple Choice 38 12:17 
   Multiple Choice 39 13:49 
   Multiple Choice 40 17:02 
   Multiple Choice 41 18:27 
   Multiple Choice 42 19:35 
   Multiple Choice 43 21:10 
   Multiple Choice 44 23:35 
   Multiple Choice 45 25:00 
   Multiple Choice 46 26:20 
   Multiple Choice 47 28:40 
   Multiple Choice 48 30:14 
   Multiple Choice 49 31:24 
   Multiple Choice 50 32:45 
   Multiple Choice 51 33:41 
   Multiple Choice 52 34:40 
   Multiple Choice 53 36:12 
   Multiple Choice 54 38:06 
   Multiple Choice 55 38:37 
   Multiple Choice 56 40:00 
   Multiple Choice 57 41:18 
   Multiple Choice 58 43:12 
   Multiple Choice 59 44:25 
   Multiple Choice 60 45:02 
   Multiple Choice 61 46:10 
   Multiple Choice 62 47:54 
   Multiple Choice 63 49:01 
  AP Biology Practice Exam: Section I, Part B, Grid In 21:52
   Intro 0:00 
   AP Biology Practice Exam 0:17 
   Grid In Question 1 0:29 
   Grid In Question 2 3:49 
   Grid In Question 3 11:04 
   Grid In Question 4 13:18 
   Grid In Question 5 17:01 
   Grid In Question 6 19:30 
  AP Biology Practice Exam: Section II, Long Free Response Questions 31:22
   Intro 0:00 
   AP Biology Practice Exam 0:18 
   Free Response 1 0:29 
   Free Response 2 20:47 
  AP Biology Practice Exam: Section II, Short Free Response Questions 24:41
   Intro 0:00 
   AP Biology Practice Exam 0:15 
   Free Response 3 0:26 
   Free Response 4 5:21 
   Free Response 5 8:25 
   Free Response 6 11:38 
   Free Response 7 14:48 
   Free Response 8 22:14 

Welcome to Educator's AP Biology course.0000

I am Dr. Carleen Eaton, and we will be starting out the course with the discussion of elements, compounds and chemical bonds.0004

Although this is a biology course, we are starting out with some chemistry basics because life involves many chemical reactions.0011

Chemical reactions occur constantly within the cells and are essential to life.0020

For example, the conversion of carbon dioxide and water to glucose using sunlight as an energy source by0024

plants is a chemical reaction, and this is known as photosynthesis.0031

Animals use chemical reactions to break down food sources such as carbohydrates, fats and proteins to release their energy to fuel cellular processes.0035

Starting from the beginning with the discussion of elements.0046

Elements are substances that cannot be broken down into simpler substances through chemical reactions.0049

Matter is anything that takes up space. Elements are a form of matter.0056

There are 12 elements on the periodic table.0065

Here, as shown one square, an example of an element from the periodic table, and this is oxygen.0070

So, there are 12 elements. Of these, 92 are naturally occurring.0075

The remaining elements can be made or created in a particle accelerator. However, only 92 are naturally occurring.0090

Although there are 9 naturally occurring elements, in biology, we are going to be focusing on mainly 4 elements.0098

Living organisms are composed mainly of oxygen, carbon, hydrogen and nitrogen.0105

There are small amounts of other elements found in living organisms, for example calcium, which is found in our bones.0119

Phosphorus and magnesium are also found in small amounts.0127

There are other elements called trace elements, and these are also essential to life; but they are found in very small or what is called "trace amounts".0131

An example of this would be iron. Iron is found in red blood cells, and it is essential in allowing us to carry oxygen using our red blood cells.0140

Iodine is another example. The thyroid gland needs iodine to function correctly, and without enough iodine, people develop a condition called goitre.0150

Here, looking at this example of oxygen on a periodic table, you will notice a couple of numbers.0159

The first is the atomic number, and we will get into exactly what this means.0166

But for right now, I just want to give you an idea of how to read the periodic table of elements.0171

O is a symbol for oxygen. Here is the full name, and then, down here, is the atomic mass.0176

A molecule is composed of two or more atoms bonded together in a specific arrangement.0189

Compounds are composed of different elements that are combined in a fixed ratio.0196

Let's look at an example of a molecule. O2 is two oxygen atoms bonded together.0203

These are molecules. However, since these are the same type of atom, this is not a compound.0210

An example of a compound would be H2O or water.0219

This is two atoms of water bonded to 1 atom of oxygen, and this is a molecule of water; and it is also a compound.0224

What you will notice here is that compounds are composed of different elements, and they are combined in a fixed ratio.0244

This is very important because if I look at water/H2O, and then, I look at H2O2/hydrogen peroxide, I will notice0249

that these are both composed of hydrogen and oxygen, however, they have very different properties.0264

Water is the solvent of life. You drink it.0268

Your body is made largely of water, whereas hydrogen peroxide has entirely different properties0273

altogether, and it is good for treating wounds for example but very different substance than water.0279

So, it is not just the atoms that are in a compound that matter. It is the ratio and the order that they are combined in.0287

Elements are composed of atoms, and these are the smallest unit that an element can be broken down to that0298

still retains the characteristic structure and property of the element.0304

Now, remember, elements are the substances that cannot be broken down into smaller particles through chemical reactions.0309

But it is possible to break down an element further, just not through chemical means.0316

And if you did break down an element further, what you could find are the different subatomic particles that comprise an atom.0319

So, let's look at what an atom is composed of. It is composed of protons, neutrons and electrons.0331

The central part of the atom is called the nucleus, and the nucleus contains protons and neutrons packed together tightly.0344

Protons are positively charged. Neutrons, as the name suggests, are neutral.0356

And orbiting around the nucleus, you will find the electrons, and these are negatively charged.0367

These electrons are held in their orbitals by their tractions to the positively charged nucleus.0381

The protons are positively charged. Electrons are negatively charged, and this attraction keeps the electrons orbiting around the nucleus.0388

Each element has a characteristic number of protons, and the atomic number I mentioned at the top of the periodic table is the number of protons.0395

So, the atomic number equals the number of protons.0403

When we talk about an atom, we are usually talking about it in its neutral form, and that neutral form would have the same number of protons and electrons.0411

If there is 4 protons that are positively charged and 4 electrons that are negatively charged, they will cancel each other out.0422

An example would be carbon. Let's go get carbon.0430

Carbon has an atomic number of 6.0435

A second number associated with an element is its mass number. OK, atomic number is number of protons.0442

The mass number is the number of protons plus the number of neutrons. The mass number of carbon is 12.0449

Now, if carbon is neutral, that means that I can determine that I have 6 protons from the atomic number, and since it is neutral, I also have 6 electrons.0464

And then, all I have to do to figure out the number of neutrons is to take this mass number,0476

subtract the atomic number, and that will give me the number of neutrons.0484

Here, the mass number is 12-6. Therefore, there are 6 neutrons.0490

Sometimes, you will see an element written as such.0502

You will see the symbol like C for carbon and then, a number at the top and a number at the bottom.0506

This is the mass number. This is the atomic number.0512

The unit of mass that we use to express atomic or molecular weights is called the unified atomic mass unit0525

or just atomic mass unit, and this is abbreviated with a U.0533

It is also the same as a Dalton- 1 Dalton. A Dalton is abbreviated Da.0546

Now, a proton or neutron has a mass of 1.7 x 10-24 grams, so that equals the mass of proton or 1 neutron.0556

If you add up the mass of the protons and neutrons, you have what is very close to the mass of the atom.0576

And the reason for this is that electrons are much, much, much smaller than protons or neutrons.0585

And their mass is, therefore, negligible. Frequently, we, therefore, talk about the atomic mass as being approximately equal to the mass number.0590

So, again, remember that the mass number is number of protons plus neutrons.0602

Since that mass of electrons is negligible, the atomic mass or the mass of the atom is approximately equal to the mass number.0609

When you look on the periodic table of elements, you will see a slightly different number, which is at the bottom, and that is more of an exact atomic mass.0628

It is a weighted average of masses of the various isotopes of the atoms, of the element, and if you just round that off, you will get the mass number.0636

OK, concept of isotopes, let's look at carbon as an example and look at the various isotopes of carbon.0646

Isotopes are forms of an element that have different numbers of neutrons.0655

Remember that for an element to be the same element, it has to have this characteristic number of protons. For carbon, there are 6 protons.0663

When we talk about this form of carbon right here that I have been discussing, carbon 12, it has 6 protons and 6 neutrons.0673

However, you can talk about isotopes of carbon. One is carbon 13.0680

I have a 1 up here for my mass number, and that means, if I took that 13, subtracted the number of protons, I would end up with 7 neutrons.0685

So, carbon 13 is a form of carbon and is much more rare than carbon 12, and it actually has 7 neutrons.0695

There is another isotope called carbon 14, and this is a radioisotope. It is a radioisotope.0703

So, if I took the mass number here - I said 1 - and I subtracted atomic number 6,0713

I would come up with 8 neutrons, and carbon 1 is actually a radioactive form of carbon.0720

This is a radioisotope. The difference between radioisotopes and other types of isotopes is that radioisotopes are unstable.0725

They actually decay spontaneously, and they give off energy in the process.0735

The nucleus decays, and the number of protons or neutrons can change.0739

The result is that it can actually decay and turn into a different element as it is decaying.0742

These are very important in medicine. For example iodine 13 or I-131 is a radioisotope.0748

I mentioned that iodine is important to the thyroid.0760

Well, if somebody has thyroid disease or thyroid cancer, we can actually infuse a radioisotope into their body.0762

It will localize to their thyroid, and it will help decrease the activity of that tissue or destroy malignant thyroid tissues.0770

So, radioisotopes do have important uses in biology and medicine.0779

To understand chemical bonding and chemical reactions, you need to understand more about electrons and particularly about the energy levels of electrons.0788

Electrons are found at different energy levels, and the levels that they spend their time in are called electron shells.0798

The outermost shell is extremely important in chemical bonds, and it is called the valence shell.0806

Let's talk about the concept of energy, a little more in potential energy.0813

Recall that the nucleus is positively charged, whereas electrons are negatively charged, so electrons are attracted to that positively charged nucleus.0818

The farther the electrons are from the nucleus, the greater, what we call, potential energy they have.0829

Potential energy, think of it as stored energy, or it is energy that is there and that could be released/has the potential to be released.0832

Think about if you were using a bow and arrow and you pulled back the bow.0842

You are using energy from your muscles. You are transferring it into the bow, and you are pulling it back.0847

Now, that bow has potential energy. It has stored energy.0851

When you let go of the bow, the arrow shoots out. The energy is transferred to shoot that arrow.0855

Now, the greater the distance you pull back the bow, the harder you pull on it,0859

the greater the potential energy stored in the bow, and it is the same idea with electrons.0866

The farther away they are from the nucleus, the farther the electron shell is that they are in, the greater the potential energy.0873

To move to a shell that is more distant from the nucleus, an electron would have to use energy.0877

To get closer, it would release energy.0890

Electrons pretty much stay within these shells, and they only pass through them on their way to a different shell.0898

Electrons fill up these lower energy shells first, and then, they go to the higher ones.0901

The first shell can hold two electrons, whereas the second shell can hold 8 electrons, and each shell has a characteristic number of electrons that it can hold.0910

Again, the outermost shell is called the valence shell, and a lot of the chemical behavior of an atom is driven by a need to fill this valence shell.0915

If the outermost shell is full, if the valence shell is full, then you have what is called an inert element.0936

Inert elements do not readily interact with other atoms. They do not have a need to.0948

Their Valence shells are already full.0957

OK, inert elements have a full valence shell, for example, neon. Neon has 1 electrons.0962

It has 2 in the first shell, and it has 8 in the second.0967

This is its valence shell. If there was more than 10, it would have to go to the third shell, but since this shell is full,0980

it is what we call an inert element, and it is not highly motivated to interact with other atoms.0988

Within valence shells, the electrons are usually found in what is called orbitals.0995

The shell gives the average distance from the nucleus where electron is found, but that is just an average.1004

Most of the time, electrons spend in particular regions called orbitals.1013

Orbitals can have various different shapes, and orbitals are listed by a number and a letter.1018

For example, this sphere is a 1s orbital. This tells me that it is in the first shell, and this tells me the shape, and so s, I just think of spherical.1025

It is a globe or round shape. Each orbital holds two electrons.1032

The first shell has only the 1s orbital that holds two electrons. That is full.1045

You need to go to the next shell. The next shell has a 2s orbital.1059

So, it is in the second shell, and it has a spherical shape. In addition, the second shell also has 3p orbitals.1065

p orbitals have this dumbbell shape, and I have only shown two here for simplicity; but in the second shell, there is one 2s orbital, and there are three 2p orbitals.1070

Each of these holds two electrons, so 2 here and 2 in each of the three orbitals. This holds the total of 8 electrons.1079

The behavior of an atom is often driven by a need, again, to fill the valence shell.1096

Let's look at an example of fluorine. Fluorine has 9 electrons.1107

That means that this 1s orbital is going to be full.1115

Here, we see these altogether. Remember, there is actually this third orbital, here, this third p orbital.1127

Draw that in, just not shown in order for simplicity, but looking at these electron orbitals with fluorine.1132

This first shell would have two electrons in it that is full, then, fluorine needs to go up to the second shell.1141

The 2s orbital here has two electrons in it, so, I used up two in the first that left me with the seven.1149

I have used up two more. I have five.1161

One of the P orbitals can hold two. Another p orbital can hold two, and this last p orbital only has one.1169

So, there is a single electron missing to complete the valence shell, and bonding has to do with completing that valence shell.1171

One thing you will also notice about molecules is they can differentiate, and the shape of a molecule1180

has to deal with the position of the orbitals; and the position and shape of the orbitals can change when bonding occurs.1187

Let's go ahead and talk about bonding. Covalent bonds are formed when atoms share electron pairs.1191

Remember that the atom wants to fill its valence shell.1198

Let's look at hydrogen. Hydrogen has one electron.1204

It has just got a single electron in the 1s orbital. That is its valence shell.1209

The first shell is the valence shell in this case, and it holds one electron. It needs one electron to fill the valence shell.1214

One way for the hydrogen to get to fill that shell would be to share an electron pair, and that is what covalent bonding is.1219

In the simplest case, hydrogen could share an electron pair with another hydrogen, so the second hydrogen is also lacking of full valence shell.1239

Therefore, if they each shared an electron pair, if they shared one electron pair, they would have full valence shells.1248

Another way to write this that helps to clarify is called a Lewis dot structure.1264

Both of the methods I have shown here show a covalent bond.1274

This is a single bond, and it means that one electron pair is being shared by the two molecules, by the two atoms.1283

So, this forms a molecule of hydrogen/H2 via sharing of one electron pair in order to complete the valence shell.1289

Atoms can share more than one pair of electron. An example would be oxygen.1301

Looking at oxygen a little bit more closely, it has 8 electrons.1311

The second shell has 6 electrons, but to have a full valence shell, it needs two more electrons.1317

Therefore, sharing just one pair of electrons would not fill the valence shell. It needs to share two pairs.1329

So, oxygen, therefore, can do that a couple of different ways.1339

Let's look at the example of CO2. That would be a carbon double-bonded to one oxygen and then, on the other side, double-bonded to a second oxygen.1347

This means, or if you looked at the Lewis dot structure, what is happening is a double bond is formed.1354

A double bond is formed when two electron pairs are shared.1366

This is sharing two electron pairs because oxygen needs to share two electron pairs in order to complete its valence orbital, and what is going on with carbon?1380

Well, remember that carbon has 6 electrons. That means the first shell contains 2 electrons, and the second shell has 4 electrons.1386

So, it needs electrons to complete its valence shell. Looking at what is going on with carbon, it is sharing 1, 2, 3, 4 electron pairs.1400

The oxygen is a full valence shell sharing 2. This oxygen has a full oxygen sharing 2, and this carbon has a full shell sharing 4 electron pairs.1411

A covalent bond is formed when the atoms share electron pairs. There are different types of covalent bonds.1422

There are polar, and there are non-polar covalent bonds. Some atoms share the electron pairs equally, whereas others do not.1434

In certain situations, an electron pair is more strongly attracted to one atom of the bond than it is to the other.1446

That would form a polar bond. When there is an equal attraction between the electron pair to the two atoms, that is called a non-polar bond.1454

For example, I talked about H2/hydrogen molecule formed by a single bond between two hydrogen atoms.1462

Since these atoms are both the same, the electron pair is going to spend equal time near both of the atoms.1472

This would be a non-polar bond. Let's contrast that with water/H2O.1481

Oxygen is what is called electronegative. It is very electronegative, and what electronegativity refers to is the attraction that a particular atom holds for electrons.1488

Electrons are more attracted to a highly electronegative atom, so the more electronegative an atom is, the more strongly electrons are attracted to it.1495

The oxygen here is more electronegative than the hydrogens, therefore, in oxygen or in water/H2O, here is some electron pairs being shared.1510

There is a pair shared here, and a pair shared here, but these electrons tend to spend more time near the oxygen atom.1535

They do not share equally their time between the two atoms. They spend more time close to the oxygen atom.1548

What that does is results in what is called a partial negative charge for the oxygen.1556

δ-, this delta symbol and then, a minus next to it means partial negative charge.1564

Since the electrons are hanging out with the oxygen more, and electrons are negative, this is going to end up with a partial negative charge.1572

Now, the opposite is going to happen with the hydrogen. It develops a partial positive charge because the electrons are1582

by the oxygen more, slightly more negatively charged oxygen, slightly more positively or δ+ over here by the hydrogen.1589

Because of the shape of water, it has this V shape.1595

This side of the molecule ends up overall slightly negative, and the hydrogen side ends up slightly positive.1609

So, this is what we call a polar molecule. H2/hydrogen molecule is non-polar.1612

Now, let's look at CO2. Again, we have these electronegative oxygens, and the electrons are more drawn to these1618

oxygens than they are to the carbon, but because this is a linear molecule, these two bounce each other out.1626

Oxygen is pulling this way. Oxygen is pulling it that way, but you do not end up with one side of the molecule that is overall1634

electronegative or overall partially negative versus partially positive charge because of this linear shape.1640

So, it is not just the atoms. It is also the configuration of the atoms that determines whether or not a molecule is polar or non-polar.1646

And in the next lecture, we are going to talk about water.1653

Water is extremely important to living beings, and the fact that water is polar gives it many important properties.1662

Another name for polar molecules like water is hydrophilic. Polar molecules are hydrophilic.1665

This means they are water-loving. They are attracted to water.1672

They dissolve in water. You might have heard the expression "like dissolves like".1684

So, polar molecules dissolve in other polar substances. Non-polar are hydrophilic or water-fearing - excuse me - hydrophobic.1689

Non-polar molecules are hydrophobic. Polar molecules are hydrophilic.1693

So, non-polar molecules do not dissolve well in water- like dissolves like. Non-polar molecules like fats dissolved in other non-polar molecules.1708

That is why oil and water do not mix.1713

If you are making a recipe, and you need to put some oil into a mixture that contains water, you will see that the oil separates out.1724

It does not dissolve in water because the oil is hydrophobic, and water is polar or hydrophilic.1726

Hydrophobic fat or lipid or oil and a hydrophilic solution such as water will not mix.1733

Alright, a second type of bond is an ionic bond.1741

Remember that in covalent bonding, the atoms share an electron pair.1753

Another way to fill the valence shell is not by sharing electron pair, but by losing or gaining an electron.1756

An ionic bond refers to the attraction between positively charged ions, which are called cations, and negatively charged ions, which are known as anions.1763

This is best understood through example, so let's look at NaCl or sodium chloride.1769

Sodium has 11 electrons. That means the first shell will contain two electrons.1780

The second shell will contain 8 electrons. This gives 10, and the third shell will have a single electron.1787

Obviously, the valence shell, the third shell, is not full.1798

Chloride has 2 electrons, the first shell, again, electrons, second shell, 8 electrons, third shell, 7 electrons.1806

This shell holds 8 electrons, so to fill its valence shell, chlorine needs one electron.1811

This problem is solved when sodium transfers an electron to chlorine to form a chloride ion.1826

OK, sodium transfers an electron to chlorine. Let's think about what would happen.1837

If sodium transfers an electron, it is going to be down to 1 electrons, but it still has 11 protons.1847

That means it is going to end up positively charged because it has one more proton than an electron.1856

So, we say this as a +1 positive charge, or we just show it as a plus.1864

In ion we could have it 2+ or 3+ positive charge. This has just a single, so it is a plus.1869

It transferred one electron to chlorine. Chlorine, in turn, now has 2 electrons.1874

It has one more electron than proton, which is going to give it a negative charge- chlorine with a negative charge.1881

It received one electron. This is, now, called a sodium ion, and this is called a chloride ion.1894

Sodium is positively charged, so it is a cation. Chloride is negatively charged, so it is an anion.1901

This step is not actually the ionic bond. It is necessary in order to get to the ionic bond.1912

But the ionic bond refers to the attraction between this positively, negatively charged ions.1922

Sodium does not just transfer the electron and then, float away.1928

In fact, these two stay associated with each other as NaCl, which is an ionic compound or salts.1939

Notice that this is not a molecule. Molecules are held together by covalent bonds.1944

It is a compound, though. It is an ionic compound.1952

These are also called salts, or this is table salt. Notice that the problem of the valence shells has been solved.1957

Since sodium lost its electron, once it loses it, there is no electrons in the third shell.1960

The second shell becomes a valence shell, and it is full.1969

Chlorine has gained an electron, and now, has 8 electrons in its valence shell; so that shell is full.1975

These two have achieved completing their valence shells, but it is not by sharing an electron pair.1979

It is by losing or gaining an electron, and then, do the positive and negative charges, they stay associated with each other.1986

Salts often form crystals, and this is because of the interactions via these ionic bonds.1991

The strongest type of bond is a covalent bond, but these other types of bonds are very important as well; and they are often called weak bonds.1999

One type of weak bond is a hydrogen bond. Now, well, a single hydrogen bond might not do a lot.2010

Many of these together can achieve something and actually have strength.2018

So, even though bonds such as hydrogen bonds are weak bonds, they are very important.2024

Let's look at water as an example of hydrogen bonding.2030

A hydrogen bond is formed when a hydrogen atom that is covalently bound to an electronegative atom is attracted to another electronegative atom.2035

Revisiting the idea of water, oxygen, hydrogen, recall that this is a polar bond that the oxygen atom is partially negatively charged,2039

while the hydrogen atoms have a partial positive charge because the electron pair favors the oxygen atom.2049

Because this hydrogen is partially positively charged, and the oxygen is partly negatively charged, there is an attraction between2066

the hydrogen and oxygen, not just the oxygen it is bonded to, but oxygens on other water molecules2075

These dotted lines indicate hydrogen bonds. Here is the covalent bonds between hydrogen and oxygen.2084

And then, this hydrogen is attracted to this nearby water, the oxygen atom.2094

This hydrogen is attracted to this nearby oxygen atom, and so a lot of complex hydrogen bonding goes on with water.2100

As you can see here, hydrogen bonds can hold different molecules together, and they can also hold parts of large molecules together.2106

For example, proteins fold into complex shapes of conformations, and those shapes2118

are often held in place by hydrogen bonding between one region of the protein molecule and another region.2125

This hydrogen bonding is responsible for a lot of the important properties of water that we are going to talk about in the next lecture.2131

Now that we have discussed bonding, we are going to go on to talk about chemical reactions, and molecules undergo reactions by forming or breaking bonds.2138

Let's look at a typical chemical reaction: CH4, which is actually methane, combines with two molecules of water, so 2 O2.2147

And those undergo a chemical reaction to form carbon dioxide/CO2 +2 molecules of water.2156

The initial substances involved on this side are the reactants. Those end up forming products.2169

The substances that you end up with are called the products.2177

Notice with this reaction, what we have is a balanced equation.2190

This equation is balanced meaning that the atoms that I have in the left, if I count those up2193

and I count up the atoms I have on the right, I have the same number and the same type.2198

No atoms were lost or gained.2203

Let's look on the left side and the right side. Let's look at carbon.2209

I have one carbon on the left. On the right, I have one carbon, hydrogen.2212

On the left, I have 4 hydrogens. On the right, I have 2 H2s, so that is 2 x 2.2216

That gives me 4 hydrogens. I also have oxygen.2228

On the left, I have x 2 oxygens. I have 4 oxygens.2236

Here, I have O2. That is two oxygens, and then, I have x O, which is two more oxygens, give me a total of four oxygens.2240

So, we say that this equation is balanced. No atoms were lost or gained.2245

They are just combined differently.2254

Reactions can proceed in both directions, so this reaction can go in reverse.2258

You could combine CO2 and two molecules of water to get back two oxygen molecules plus a methane molecule.2261

If the ratio is not changing, we say that the reaction is in equilibrium, if ratio of the molecules is unchanging.2268

Now, that is not to say that I am going to have exactly equal amount of methane and CO2.2277

It means the ratio is not changing. In fact, often, a reaction favors one direction.2299

So, maybe this reaction favors formation of CO2 and water.2304

In that case, I might have 10 molecules of CO2 for every molecule of methane, but if the ratio is not changing, I still maintain that ratio.2309

We say that the reaction is in equilibrium. I am not gaining more and more CO2 relative to methane, then, the reaction is in equilibrium.2315

Now, when we deal with chemistry and chemicals, we are dealing with very, very small amounts.2327

And it would not really be practical to just use grams when we are talking about molecules and chemicals and atoms.2339

Since the mass is so small, chemists have developed a different system with which to measure molecular masses and concentrations of chemicals and solutions.2345

A mole is simply a number. It is 6.02 x 1023.2352

If you say you have a mole of something, you are saying you have 6.02 x 1023.2364

This is no different than saying you have a dozen of something.2370

If you say "I have a dozen apples", you are saying "I have 12 apples", the same way you could say "I have a mole of apples", "I have 6.02 x 1023 apples".2375

You could say you have a mole of glucose, 6.02 x 1023 glucose molecules.2379

This number, 6.0 x 1023, is known as Avogadro's number, and it is named after an Italian physicist.2390

Let's talk about molecular mass and moles. If you take a sample of an element that is equal to its atomic mass, you will have one mole of that element.2397

Take a sample of an element equal to the element's atomic mass. You will have one mole of the element, for example carbon.2415

Carbon has an atomic mass equals 12.2432

Therefore, if I take 1 grams of carbon equals 1 mole of carbon, that means that in 12 grams of carbon, you will have 6.02 x 1023 carbon atoms.2468

Now, let's say you are not just dealing with a molecule - excuse me - an element. Let's say you are dealing with a molecule.2476

I know for an element, that I just have to look at the atomic mass, take that amount in grams, and I have a mole.2498

In order to find a mole of a molecule, I need to find the molecular mass of the molecule.2506

Molecular mass equals the sum of the masses of the atoms in the molecule.2508

Simple example, water/H2O, here, I have two hydrogen atoms and one oxygen atom.2512

Hydrogen has a mass of 1. Oxygen has a mass of 16.2540

I am going to take one hydrogen atom with a mass of 1 plus the second hydrogen ion with a mass of 1 plus an oxygen atom with a mass of 16, and I am going to get 18.2548

This is the molecular mass. If I take a sample of 2 grams of water, this is going to equal mole of water or 6.02 x 1023 molecules of water.2559

Something else to understand is that let's say I had a dozen water molecules. Let's talk about a dozen instead of a mole.2575

I can say "oh, I have a dozen water molecules", and then you ask me how many hydrogens I have.2594

Well, if I broke up the water, the dozen water molecules, it ends up just hydrogens and oxygens.2601

Each water molecule has two hydrogen atoms, so actually, it would have 2 hydrogens and 12 oxygens in that water, in that dozen.2606

So, if I said I have a dozen water molecules, that means I have a dozen water molecules.2612

But if I broke them up, I would actually have two dozen hydrogen atoms and one dozen oxygen atoms.2626

In that same way, if you have a mole of water and you broke it up, you would end up with 2 moles of hydrogen atoms and 1 mole of oxygen atoms.2631

This has to do with mass, and when you are working with dry or just certain chemicals, it is very helpful; but a lot of times, we are working with solutions.2639

And when we work with solutions, we talk about molarity.2660

A 1 molar solution - and we will often write this as 1 mole - equals 1 mole of a substance dissolved in 1 liter of solvent, and it can be written as 1M as shown.2670

For example, let's say I wanted a 1 molar solution of glucose. Glucose has the molecular formula C6H12O6.2678

I need to figure out the molecular mass. OK, so I have glucose, and I want a 1 molar solution.2709

The molecular mass of glucose is going to be the mass of carbon, which is 12 times I have 6 carbon atoms2727

plus the mass of hydrogen, which is 1 x 12 hydrogens plus the mass of oxygen, which is 16 x 6 oxygen atoms.2754

And if you add these up, you will get 180. Therefore, the molecular mass of glucose is 180.2766

In order to get a molar solution of glucose, dissolve 180 grams of glucose in 1 liter of water.2779

OK, molarity, to make a 1 molar solution, figure out the molecular mass.2788

That will tell you how much of something you need, how many grams you need to get 1 mole.2813

So, I have 6.0 x 1023 glucose molecules and 180 grams of glucose, and I am going to dissolve that in 1 liter of water; and I will have a 1 molar solution.2821

Alright, let's try out some examples now.2827

Example 1: the atomic number of fluorine is 9, and its atomic mass is 19. How many protons, neutrons and electrons does it have, is it inert, why or why not?2841

Remember that the atomic number equals the number of protons.2844

The atomic mass, we often use interchangeably with mass number, although they are not exactly equal.2858

Because the mass in electrons is negligible, we often use them interchangeably, so the atomic mass equals 19.2868

In this case, we are using that as a mass number as well, and therefore, if I know that that is equal2876

to the number of neutrons plus the protons, then, I simply take 2 - 9 - so the atomic number is 9 - to give me 10 neutrons.2885

Alright, let's keep track of what we have. We have the atomic number.2897

Protons equal the atomic number equal 9. Neutrons, I am just taking the mass number, which is the number of neutrons and protons.2914

And I am subtracting the number of protons from that, and that leaves me with 10 neutrons.2919

In its neutral form, the number of protons and electrons will be equal, so I am going to have 9, 9 protons, 10 neutrons, 9 electrons. Is this inert?2934

Well, remember that an inert element has a full valence shell, so let's look at the electron situation.2938

I have 9 electrons. In the first shell, I have two electrons.2949

The second shell is going to have seven electrons. This is the valence shell.2957

This shell holds 8 electrons. Therefore, this is short 1 electron.2963

This does not have a full valence shell, so it is not inert because its valence shell is not full.2970

Second example, we have a chemical equation here.2981

Example 2: 6 carbon dioxides plus 6 water molecules gives...it is actually glucose plus oxygen.2991

This equation shows the formation of glucose, what coefficients needed to be placed in front of the products in order to balance the equation.2996

A balanced equation means you are not going to lose anything in terms of atoms or gain any atoms between reactants and products.3005

Reactants for carbon, I have 6 carbon molecules, products, 6 oxygen. 6 x 2 is 12, plus 1 is 13.3012

Here on the right or...excuse me, correction. This is 6 x 2 is 12, and then, 6 x 1 oxygen in each of the 6 water molecules is 6.3026

So, that is going to be actually oxygen is going to be x 2 is 12 + 6 more to give me 18.3044

On the right, I only have 6 + 2, and we have 8; so I have got a problem right here. This part is not balanced.3058

Hydrogen, x 2 is 12. On the right, I have 12, so I need to fix the oxygen, and you can actually use fractions.3070

You could use fractions on the left to fix it, make this number of oxygen smaller, but it would actually be easier to just use a whole number on the right.3078

Since the carbons are correct, and the hydrogens are correct, I do not want to mess with this, with the glucose.3092

I just want to focus on the oxygen where the problem is, so I am going to try some different coefficients.3100

I need quite a few more, so I am going to start out with 4. I am going to try putting a 4 in front of this and see what happens.3106

Now, I have 6 oxygens + 4 x 2, which is 8, 8 + 6 = 14.3112

That is not enough, so let's try a coefficient of 5. I have six oxygens here plus x 2 is 10.3119

That is 16. Remember, I want 18, so that is not big enough.3128

Let's try again. x 2 is 12, plus the 6 I have here, is 18.3141

Therefore, a coefficient of 6 in front of this O2 will balance this equation because now, I would still have my 6 carbons on both sides.3145

I solved my 1 hydrogens, and now, I have 2 oxygen on the left and then, 18 oxygen atoms on the right, so this is now a balanced equation.3153

Example 3: KCl/potassium chloride is a salt that disassociates into potassium and chloride ions. What type of bond holds KCl together?3165

Describe this type of bond and how it is formed. Well, this is a salt and this dissociates to form ions, therefore, it is an ionic bond.3175

This is formed by the attraction between the negatively charged chloride and a positively charged potassium ion.3187

What had to happen for this to occur is that potassium transferred 1 electron to chlorine.3198

The result is that there was one with more proton than electron left on potassium, and you ended up with potassium ion.3215

Chlorine got an extra electron and became the negatively charged chloride ion, and these two are attracted to each other due to their opposite charges.3228

So, this is an ionic bond.3239

Example 4: sucrose or table sugar is given by their formula C12H22O11.3251

What mass of sucrose in grams will need to be added to 1 liter of water to make a 1 molar solution of sucrose?3256

Remember that a 1 molar solution is 1 mole of a substance dissolved in 1 liter.3264

Remember that in order to figure out how much of a substance you would need to get a mole, you need to figure out the molecular mass.3271

So, I need to figure out the molecular mass of sucrose, of C12H22O11.3303

The atomic mass of carbon is approximately equal to 12 just counting electrons, so it is the carbon atomic mass.3311

Hydrogen mass is 1, and the mass of oxygen is 16.3324

Therefore, I am going to have 12 carbons x the mass of 12 + 22 hydrogens x the mass of 1 + 11 oxygens times the mass of 16.3342

And if you figure this out, 12 x 12 as it comes out to 144 + 22. 11 x 16 is actually 176, so that is 342 grams.3350

Therefore, I would need to add 342 grams of sucrose to 1 liter of water to form a 1 molar solution.3364

Thanks for visiting Educator.com, and I will see you next time.3377

Welcome to Educator.com.0001

Today, we are going to be focusing on water, and water is essential to life. In fact, we are composed mostly of water.0003

Organisms need water to survive, and marine organisms actually are immersed in water.0011

We are going to talk about water and some of its special properties starting with the molecular structure of water.0017

Water is given by the formula H2O, and it consists of one oxygen and two hydrogen molecules.0028

It is a polar molecule, and if you need a review of the concept of polar and non-polar molecules, then, go back and look at the previous lecture.0041

I talked about that in detail, but here, I am going to do a review.0051

Remember that the electron pair shared between a hydrogen, and an oxygen molecule is not equally shared.0057

Oxygen is more electronegative than hydrogen, and that means that it more strongly attracts electrons.0066

As a result, the electrons spend more time near the oxygen atom than it do by the hydrogen atom.0074

This ends up giving oxygen a partial negative charge or δ-.0082

And since the electron pair spends less time by the hydrogen atom, the hydrogen atom ends up with a partial positive charge or δ+.0088

Now, one important concept or theme in biology is that of emergent properties.0104

Emergent properties are properties that emerge or come into being at higher levels of organization.0109

For example, if you just took 1 heart cell and looked at it in a petri dish, it could not pump blood.0116

But, if you put many cardiac cells together, they can pump blood.0121

So, that build in the pump blood is something that emerges when you put many cells together at a more complex level of organization.0125

And we are going to see this all the way through the course, but here, if you take a single molecule of water, it is held together by covalent bonds.0132

But, if you put many molecules together, they hydrogen bond, and new properties emerge as a result of this hydrogen bonding.0140

Looking back here at this single molecule of water, water is V-shaped.0149

And because of that and the fact that the oxygen is a partial negative and the hydrogen is a partial positive charge,0152

the overall molecule is polar meaning 1 side is relatively negative and the other is relatively positive.0159

Now, let's look at multiple oxygen, multiple water molecules associated with each other.0168

Even though a particular hydrogen is covalently bonded to a certain oxygen, it also is attracted to nearby oxygen molecules.0175

Here, we have the δ-, and on the hydrogens, δ+.0185

Even though this hydrogen is covalently bound to this oxygen, it is also attracted to a nearby electronegative oxygen molecule.0197

And this attraction shown by these dotted lines is known as a hydrogen bond.0207

Recall that hydrogen bonds are weak bonds, whereas covalent bonds are strong bonds.0213

A single hydrogen bond is not going to do much, but many together can be strong; and they account for many of the special properties of water.0217

In the natural world, you will actually find water in all 3 of its forms: liquid as water vapor - oh, excuse me - liquid as liquid water.0226

We will also find the gas form, which is water vapor, and finally in the solid form, which is ice.0241

In liquid water, the hydrogen bonds are constantly breaking and reforming with each other, whereas solid water,0254

which is ice that I have been talking about in a few minutes, is in more of a set structure, and that gives ice its specific properties.0263

So, let's go on and talk about some of these special properties of water.0272

Water's special properties make it essential to life, and some of these properties are that water0278

is both strongly cohesive and adhesive, that it has a high surface tension and a high heat capacity and a high heat of evaporation.0284

Let's just take these one at a time, first of all cohesion. Cohesion is the tendency of molecules to stick together.0296

Water is highly cohesive. The reason it is highly cohesive is because of the hydrogen bonding.0313

As I mentioned, adjacent molecules of water are held together by hydrogen bonding, so they stick together.0319

Looking at how this can affect biology, when we talk about plants, we are going to talk about transpiration.0327

This is the process by which water is drawn out from the roots of a plant all the way up to the plant and then, evaporates out the leaves.0336

And this can be hundreds of leaves with the tree.0344

So, what happens is as a molecule of water is lost from the leaf, as it evaporates, the next molecule gets pulled up.0348

One after another, these molecules of water pull each other up.0358

And they do so through tubes called xylem, tubes that carry water in plants, throughout the plant.0362

Cohesion is one property of water that allows for transpirations.0377

Now, adhesion is slightly different. This is the tendency of molecules to stick to other substances.0383

Cohesion, water sticking to itself well, so it is cohesive.0394

It is also highly adhesive and sticks to other substances, tendency of molecules to stick to other substances.0398

So, not only is water cohesive, it is adhesive, and if we think again about the xylem, the water is being pulled up one after another by cohesion.0411

It is also helped by adhesion, though, because the water molecules adhere to the sides of the xylem.0421

If you look in a glass of water, have you ever seen a drop just sticking to the side? That is an example of adhesion.0427

The water is cohering to itself, but it also adhering to the side of the glass.0434

Surface tension is a related concept. Water has a high surface tension, and this is what allows water bugs to actually walk across water.0440

High surface tension substances can often be thought of as having like a film across them.0455

And it is actually harder to break through that top layer to break through that film than it is to move around once you are in the water.0458

So, we take more energy to break through the surface, than it is to move once you are under.0465

And the reason is because the water molecules are hydrogen bonded to each other.0469

Underneath the surface of the water, each water molecule is surrounded by many, many other water molecules.0478

And it has that attraction through hydrogen bonding to the molecules around it.0484

Underneath there is molecules on all sides, and there are hydrogen bonding to each other.0491

Now, if you look at the surface layer, though, at the surface, these molecules are attracted to each other and the ones beneath.0497

But there is no water molecules above. Therefore, their attractive forces are concentrated among fewer molecules.0513

So, here, the attractive forces are dispersed among many molecules.0521

Here, since there is no water molecules above, the bonds between the adjacent molecules and the ones below would be stronger.0525

The result is that the molecules here are more cohesive than the ones underneath, and that accounts for the high surface tension of water.0535

Alright, we covered cohesion, adhesion and surface tension.0551

Now, we are going to talk about heat capacity. OK, now, we are going to talk about heat capacity and heat of evaporation.0555

Water has both a high heat capacity and a high heat of evaporation.0563

In order to understand heat capacity, we need to talk about the concept of specific heat.0569

Water has a high specific heat, and that is what gives it its high heat capacity.0578

Specific heat is the amount of heat a substance needs to absorb to increase its temperature.0594

And, being a little more exact about that, it is the amount of heat a substance0602

needs to absorb to increase the temperature of 1 gram of the substance by 1°C.0613

This is one way that we measure it.0634

So, just in general, specific heat talks about the amount of heat a substance needs to absorb in order to raise the temperature.0637

But talking about it in specific units, one way to measure it is in calories, which is a way to measure heat: calories per gram per °C.0643

This is one way to measure specific heat.0660

OK, so looking at this a little more carefully, if something has a high specific heat,0663

if this is a large number, then, that substance is going to need a lot of heat in order for the temperature to change.0668

So, something with high specific heat is going to be harder to heat up. It is going to be harder to raise the temperature.0675

It is going to require a greater input of energy.0682

Water's specific heat/specific heat of water is 1 calorie per gram per °C, and that is actually a relatively high specific heat.0687

Let's look at it in different units that are commonly used.0708

A Joule is another unit that is used to describe energy, and specific heat is often given in Joules per °C per gram.0712

So, let's compare some different substances using this measure.0728

In this measure of units, water has a specific heat of 4.18 Joules per calories per gram.0731

Compare that to, say, lead. Lead only has a specific heat of 0.13, and ethanol alcohol, 2.44.0741

That means that it would take twice as much energy almost to raise water.0753

1 gram of water by 1°C as it would for the ethanol and 40 times more to raise water by 1°C than it would to raise the lead.0760

And this is very good for life because if we were comprised of a substance that had a low specific heat,0775

then, as soon as it got a little bit hot outside, inside, our body would more easily heat up.0783

So, specific heat is measured as I have shown, and water has a high specific heat; and the result is a high heat capacity.0791

This was background to understanding the high heat capacity.0799

High heat capacity means a substance...you can think of it as a substance can absorb0809

more energy or more heat because heat is energy with a smaller change in temperature.0821

Something with a high heat capacity can absorb a lot more heat than something with a low heat capacity and still maintain its temperature.0836

Looking at this with a concrete example, if you are cooking and have a metal pan and the handle is metal as well,0845

within a few minutes, you are not going to want to pick up that pan without a pot holder because you will burn your hands.0852

That is because metal has a lower heat capacity.0857

So, as soon as you turn on that burner, and the heat gets on the metal, temperature of the metal is going to rise.0860

What you want is a handle that has a low heat capacity because that same amount of heat will be absorbed by the handle.0870

The temperature of the handle will not change or it will not change very much, and then, you can touch the handle.0877

Thinking of water that way, marine life live in the ocean, and they are a lot better off being in a substance that has a high heat capacity0882

because even if it gets very hot out, it is a hot summer day, it is 100° out, the ocean is not going to suddenly heat up.0891

Or conversely, if it cools down, the water temperature will still not change or fluctuate as much.0899

And it is not just for organisms that live in the water, but since most organisms are mostly made up of water,0908

again, to keep our internal temperature constant, it is important that we are made out of a substance that0913

has a high heat capacity and does not just have these big fluctuations in temperature.0919

OK, so that was heat capacity, and now, let's talk about heat of evaporation.0927

The heat of evaporation, or sometimes it is called the heat of vaporization, has to do with converting water or substance from its liquid form to its gas form.0937

And this has to do with the amount of energy it would take to convert from liquid to gas.0950

If something has a high heat of evaporation, it is going to take more energy to get the0957

molecules moving quickly enough in order for them to break free of their hydrogen bonds and form a gas.0964

That unites the concept of both the heat capacity and the heat of evaporation.0977

It has to do with the speed the molecules are moving up because looking at actually the concept of temperature, temperature is actually due to kinetic energy.0981

Temperature is the average kinetic energy of the particles of a substance.0993

Heat is energy, so molecules with a greater kinetic energy that are moving faster, they will be hotter, and they will have a higher temperature.1007

Therefore, let's think of what this has to do with hydrogen bonding.1019

Water molecules are hydrogen bonded together.1023

In order to heat up water, you need to get the molecules to move faster.1026

In order to get them to move faster, you have to break the hydrogen bonds, and that takes extra energy.1027

And that is why water has a higher heat capacity and a higher heat of evaporation because if you are talking about a substance1032

that is not hydrogen bonded together, and you add some energy, those molecules are going to speed up right away.1040

Whereas with water, first you have to use some energy to break the hydrogen bonds, then you can start speeding up the molecules.1048

Therefore, to raise the heat of something or to get it to vaporize, you need to add energy.1056

And you need to add more energy when a substance is hydrogen bonded together like this.1060

Again, the special properties of water are really closely related to the hydrogen bonding that occurs.1066

Recall that one mechanism that we use to cool ourselves is sweating, and what sweating is, is the conversion of water from its liquid form to its gas form.1075

It is the evaporation of water from our skin. In that process, water absorbs heat, and that is what is going to cool us down.1083

One more property of water that is very important that is not listed here but that is related, is the fact that ice is less dense than water.1096

In other words, the solid form of water is less dense than its liquid form, and this is an unusual property.1109

In most of substances, the solid form is more dense than the liquid form.1117

And this is another property that makes water very important especially for life in the ocean.1120

Thinking about hydrogen bonding, if the molecules are moving more quickly, then, the hydrogen bonds are going to break.1129

And in liquid water, the bonds are constantly breaking and reforming.1139

And then, when those bonds break eventually, if things are moving fast enough, and enough for those bonds to break, then, water can vaporize.1142

So that is as things speed up, the hydrogen bonds break.1151

Let's look at the opposite.1152

The freezing point of water is going to be 0°C.1155

So, as water gets cooler and cooler as the temperature drops, that is going mean that the average kinetic energy is less.1163

And kinetic energy is the energy of motion, so as the temperature cools, the water molecules are going to move slowly.1174

The more slowly they move, the more chance to hydrogen bond.1183

Eventually, they are going to get to the point where they form hydrogen bonds with the 4 adjacent water molecules.1184

And this ends up forming a very stable lattice type structure, where the different water molecules would be bonded to each other.1194

And they would form a lattice.1203

This is just really schematic.1206

But if they are forming a lattice, and let's say there is a water here, a water here, a water here, a water here,1208

and they are in this regular formation, this lattice structure is going to hold the water molecules at a certain distance from each other.1212

And it holds them a bit farther apart than they would be in their liquid form, and that is why ice is less dense than water1219

because the water molecules form a lattice structure through hydrogen bonding to 4 nearby molecules.1228

As a result, ice is actually about 10% less dense than water, and ice floats.1236

Because it floats, animals, fish, living in, say, a frozen lake will be insulated.1247

That layer of ice is going to form insulation, and it is going to prevent the change in temperature in the dead of winter.1256

This formation of ice and the fact that ice floats because it is less dense than water is another property of water that makes it essential to life.1265

In the last lecture, I introduced the concept of molarity and just briefly talked about solutions.1277

Now, we are going to cover this in detail, first some terminology.1283

When we talk about solutions, first of all, we are talking about a homogeneous mixture formed by combining a solvent in a solution.1288

Homogeneous means it is dispersed equally throughout.1298

So, if you would just take a rock and throw it in a glass of water, that is not a solution because it is not a homogeneous mixture.1300

A solvent is the liquid in which the substance is dissolved.1309

So, if I have a glass of water, and I put some sugar in it or salt, then, the water here would be the solvent.1313

And let's say I had salt, sodium chloride, that would be the solute.1325

The solute is the substance that is being dissolved. The solvent is the one that does the dissolving.1333

This mixture, altogether, is called a solution.1339

Water is a very good solvent for many substances, but recall that it is polar.1344

Water is polar, and since like dissolves like, polar substances are going to dissolve well in water. Non-polar ones will not.1352

So, polar dissolve in polar. Non-polar dissolve in non-polar.1366

Like dissolves like.1375

Looking in at an example of this, let's look at glucose.1378

This is a structure of glucose. Glucose is a polar molecule.1381

It has these hydroxyl groups that are polar centers, and on these groups, you have water.1387

You have - excuse me - oxygen with the partial negative δ- and a hydrogen with δ+.1392

Water - we already talked about - also has polar structure, δ+ and a hydrogen, δ-, so partial negative charge on the oxygen.1399

Since these are polar, these 2 are attracted to each other, and what will happen is water can dissolve polar molecules and also ions1415

because they have a positive and negative charge by bonding to them and them, and then, forming what is called a hydration shell.1423

This hydration is going to separate out the molecules in a solute, so let's say I dissolve glucose and water.1431

I just drop a lump of glucose in the water, these water molecules are going to be attracted, and glucose will be attracted to the water.1440

And eventually, it is going to separate out the glucose molecules from each other.1449

And these are going to disperse until they are evenly distributed throughout the water.1453

Non-polar molecules do not have the same attraction for water, so they are not going to dissolve well in here.1458

Like dissolves like, so if you take a teaspoon of oil, drop it in water, you are going to watch it.1466

It would separate out. Even if you stir it, it is just going to separate right back out1472

because hydrophilic molecules - you will hear this term - or water-loving are polar.1477

So, glucose or sodium chloride which disassociates to form sodium, which is charged, and chloride, these are ions.1485

So, then, the polar water molecules also partially charged. These are going to be attracted.1498

Hydrophilic molecules are polar. Hydrophobic are non-polar like lipids, and this is very important in biology.1505

We are going to see when we talk about the cell structure that the cell membrane because it contains many non-polar lipids, large polar1514

molecules cannot cross the cell membrane without help, and that is important in regulating what gets in and what does not get into the cell.1525

Polarity also accounts for certain properties of the cell.1533

When we discuss solutions, we discuss sometimes whether they are acidic or basic or acidic or alkaline.1541

Acids can be thought of as substances that increase the concentration of hydrogen ions in a solution.1551

Bases decrease the concentration of hydrogen ions in a solution.1560

And just to add to this, one common way for bases to accomplish this is bases may do so.1564

So, they might increase the hydrogen ion concentration in the solution by increasing the hydroxide ion concentration.1576

Alright, let's just look at water. Water can actually have an acid-base reaction.1587

It can disassociate into hydrogen ions plus hydroxide ions.1595

It would actually be...and if you look, it is all balanced. We have 2 hydrogen, 2 hydrogen and 1 oxygen.1605

When it dissociates in the ions, when this hydrogen pulls away, it actually leaves behind its electron.1615

This hydrogen ion leaves behind its electron and becomes positively charged.1624

You end up with a positively charged hydrogen ion, and the OH that is left behind has an extra electron, so it is negatively charged.1629

Just for a moment to be clear, though, this is actually not going to just float around by itself.1638

What is going to happen is it is going to be associated with another water molecule, so there will be another H2O.1642

And this is actually in a form that is bound to that, and it forms to what is called a hydronium ion.1651

But for simplicity, we are just going to refer to it as a hydrogen ion.1657

It dissociates in the hydrogen ion, in hydroxide ion, but you should know that in reality, this is not floating around.1660

Usually, it is part of a hydronium ion.1669

OK, overall, though, water mostly exists in this state, H2O, so this reaction, the equilibrium is very far to the left, and water is actually neutral.1681

However, some substances like to disassociate, and they do disassociate and they are, therefore, very acid or very basic.1690

Water mostly exists like this, not a lot of loose hydrogen ions and hydroxide ions floating around, so it is pretty much neutral.1700

Let's look at what is called a strong acid. A strong acid is one that is going to really have a reaction where it completely wants to dissociate.1711

Hydrochloric acid/HCl - this is hydrochloric acid - is a strong acid. It dissociates to form hydrogen ions and chloride ions.1725

In the reaction, equilibrium is to the right, so if I took a cup of water, and I threw some hydrochloric acid in it1734

this is going to dissociate, and there is going to be a lot more hydrogen ions floating around.1743

And that is going to increase the concentration of the hydrogen ions in the solution.1750

Since this is increasing the concentration of hydrogen ions in the solution that I make, it is an acid.1755

And it is a strong acid because it dissociates almost completely.1763

Let's look at a base. Let's look at a strong base to start with.1768

KOH/potassium hydroxide, this is going to dissociate to form potassium ion plus hydroxide ions.1780

Now, as I said, bases may increase or may decrease the concentration of hydroxide ions indirectly through the formation of hydroxide.1789

A base dissociates to KOH, then, the hydroxide combines with hydrogen ions that are floating around to form water.1802

The result is going to be a decrease in the concentration of hydrogen ions.1815

So, again, a base decreases the concentration of hydrogen ions in a solution.1820

It can do so directly or indirectly. Here, it is happening indirectly.1826

But we recognize that when we see something dissociating from a hydroxide ion, the end result is going to be decreasing the hydrogen ions.1831

Acids raise the hydrogen ion concentration, bases decrease.1841

Sometimes we call these acids, hydrogen ion donors because they increase the level.1846

And sometimes we call bases, hydrogen ion acceptors because they will accept a hydrogen ion, and thus, decrease the concentration of hydrogen ions.1857

So, you can think of this as base is accepting. The base is accepting a hydrogen ion, and acid is donating a hydrogen ion.1868

Another example is ammonia, and let's look at what happens with this.1882

This is a base. Now, it does not form hydroxide ions, in fact, it actually lowers the concentration of the hydrogen ions directly.1892

It is a hydrogen ion acceptor.1901

Ammonia will combine with hydrogen ion to form ammonium. In doing so, it directly lowers the hydrogen ion concentration in a solution.1905

For example, if I had water, and I threw some ammonia in it, that ammonia would bind with these hydrogen ions and form ammonium.1930

And I would end up with a solution that is more basic because it is lower in hydrogen ion concentration.1942

Just some properties of acids that you might hear about, acids turn litmus paper red.1951

We are going to talk about pH and pH paper and measuring pH, which is a way of measuring how acidic or basic a substance is.1958

Acids turn litmus or pH paper red, and they tend to taste sour.1966

An example would be lemon. Lemons are acidic.1974

Bases turn litmus paper blue, pH paper, they turn it blue. They feel slippery.1977

They taste bitter. An example would be soap.1990

I said that bases feel slippery just like if you think about what soap feels like. It is very slippery.1996

Buffers are very important in organisms because buffers resist the change in pH.2003

If you added hydrochloric acid to a solution, the solution is going to become more acidic.2015

If you add hydrochloric acid plus a buffer, the acidity will change less than if you just added the hydrochloric acid alone.2023

So, what these do is they minimize changes in the concentration of hydrogen ions, and they do this by accepting.2033

They accept hydrogen ions when an acid is added, and they donate hydrogen ions when a base is added, so they resist change.2048

Our blood has a pH of around 7.4, and if the pH goes out of that range, it can be very detrimental to life.2072

So, in order to prevent that change, we have buffers.2080

A very important buffer in our blood is carbonic acid. H2CO3, this is carbonic acid, and this is a weak acid.2085

And its corresponding base, it dissociates to form H+ plus bicarbonate/HCO3-.2096

Most buffers are weak acids and a corresponding base or weak bases and a corresponding acid.2109

And I am actually going to - with weak acids and bases - we show the reaction going in both directions.2115

Because unlike with strong acids that just want to completely disassociate, these do not- the reaction is going back and forth.2121

So, let's think about this.2129

If the blood becomes too acidic, that means that the concentrations of hydrogen ions is too high.2131

What bicarbonate will do is it will bind to these hydrogen ions, and these will actually move to the left; and carbonic acid will be formed.2137

So, you can think of it as absorbing the excess hydrogen ions.2145

Now, let's say a base is added to our blood. The base is going to decrease the concentration of hydrogen ions.2148

The buffer will minimize that change or mitigate it by dissociation and thus, donating hydrogen ions.2154

Buffers resist change in pH by donating hydrogen ions if need or accepting them if needed.2164

They are going to go the opposite way of whatever.2172

If you have added an acid, the acid increases the hydrogen ions. The buffer will take those up.2175

If you add a base, the hydrogen ion concentration decreases. The base will donate.2180

It does the opposite to keep things stable.2186

And I have mentioned pH, which you have probably heard of before, but let's go into some detail about this.2190

pH is a scale that we use to describe either how acidic or alkaline a solution is, and it is on a scale of 1 to 14.2196

Neutral is right here at 7.2207

Distilled water would be here at 7.2211

So, pH, it is often paper and you can dip it into the solution, and then, look at the color change.2217

And like I said, acids are on the red end, and then, bases are on the blue end.2224

If something is more basic - OK - or alkaline equals a higher pH, which equals a lower concentration of hydrogen ions,2232

hydrogen ions move in the opposite direction as the scale.2247

Less hydrogen ion concentration, more basic higher pH, more acidic.2253

Remember that if something is an acid, it donates hydrogen ions, so more acidic equals a lower pH.2259

And that is going to equal a higher concentration of hydrogen ions.2268

So, the scale moves the opposite way as the concentration of hydrogen ions.2275

Just to give you some examples, stomach acid is around here in the 2 to 4 range.2281

Most of our body, the pH is around 7.4, so blood is right here at around 7.4.2289

Distilled water is at 7.2297

Stomach contents, stomach acid is in the 2 to 4 range, so it is acidic, and the enzymes in our stomach work very well at that low pH.2301

Vinegar is an acid. Vinegar is around 3.2311

OK, vinegar is around 3. It is acidic.2323

A base, an example would be baking soda. That is a base, and that has a pH of about 9.2328

It is important to know that this is a logarithmic scale.2337

That means that if I am looking at, say, vinegar with a pH of 3, and then, I measure some stomach acid, and it has a pH of 4,2344

the difference between these is actually pretty large. It is actually ten times.2354

So, a pH of 4 is ten times more basic than a pH of 3, or you could say that pH of 3 is ten times more acidic than the pH of 4.2360

If I went from 3 to 5, it would be 10 x 10 or 100, so each unit is a tenfold difference.2374

And the reason we measure it this way is that there is a very wide range of how acidic or basic a solution can be.2382

And in order to just have a nice, condensed, compressed scale that is not going to be humongous, we use logs just to condense it.2388

And then, we can show a big range on just a small scale.2395

What pH actually is, is the negative log of the hydrogen ion concentration.2400

At a pH of 7, what you have is 1 x 10-7 moles per liter of hydrogen ions.2410

This is hydrogen ion concentration, and right here at 7, we would have 1 x 10-7.2428

If we went up or if we went down one, then, it would be increase in the hydrogen ion amount by a factor of 10.2434

OK, again, pH, important points: low numbers are acidic. High on the pH scale is basic.2447

Acidic represents a high concentration of hydrogen ions. Basic represents a lower concentration of hydrogen ions.2454

Water is neutral at around 7.2462

This is a logarithmic scale, so moving one unit translates to a tenfold difference in how acidic or basic or in a hydrogen ion concentration.2466

Alright, starting with example one: how is the shape of water molecule related to many of the special properties of water?2480

Recall that water is V-shaped.2487

Many of the special properties of water are due to the fact that it is polar.2494

This polarity allows for hydrogen bonding with nearby oxygen molecules.2500

Because water is V-shaped, one side of the molecule ends up being relatively negative and the other, relatively positive.2507

Oxygen is electronegative. It attracts the electron pair more strongly than the hydrogen, has a partial negative charge.2517

The hydrogen ions - excuse me - the hydrogen atoms have a partial positive charge. Therefore, it is polar.2525

This end of the molecule is relatively negative. This is relatively positive.2532

If it were a linear molecule, it would not have this polar nature. Because of this polar nature, hydrogen bonding occurs.2537

Hydrogen atoms that are covalently bound to one oxygen, are still attracted2550

to other nearby oxygens because these are also partially negatively charged, and they form hydrogen bonds.2558

The polarity of water allows for hydrogen bonding, and it is this hydrogen bonding that accounts for many of the special properties of water.2565

List five special properties of water.2575

So, we talked about why these properties exist, so what are they?2579

Well, first of all, water has a high heat capacity.2583

It also has a high heat of vaporization or you could call it heat of evaporation.2592

So, it takes a lot of heat, a relatively high amount of heat to change the temperature of water.2602

And it takes a relatively high amount of heat to change water from its liquid form to its gas form.2609

Water is strongly cohesive. Water molecules stick together.2617

Water is strongly adhesive. Water molecules also stick to other substances pretty well, very well.2626

It has a high surface tension.2635

Because of the hydrogen bonding at that surface layer, it is a little bit harder to break through the surface layer.2640

And that forms essentially a film. It can be thought of as a film across the water.2647

In addition, the solid form, which is ice, is less dense than the liquid form of water.2655

This is because of the stable lattice structure that is formed by hydrogen bonding at low temperatures.2667

The result is that ice floats. The solid form of water floats on the liquid form.2674

These are six properties. It has only asked us to name five, but any five of these would have sufficed.2681

Lemon juice has a pH of 2. Milk has a pH of 6.2689

How many times more basic is milk than lemon juice?2693

OK, pH of 6, that is milk, so we could say 6, 5, 4, 3, 2, and over here, at a pH of 2 is lemon juice.2696

Lemon juice is more acidic than milk, and milk is relatively basic.2714

It is basic. It is more basic than lemon juice.2721

So, this is asking how much more basic or you could rephrase it the other way: "how much more acidic is the lemon juice?".2725

Because this is a logarithmic scale, each unit represents a tenfold change.2731

So, going from 2 to 3 is tenfold, ten times. 3 to 4 is a tenfold change, 4 to 5 and then 5 to 6.2736

So, going from 2 to 6, I am going to be changing, increasing tenfold times another 10, times another 10, times another 10.2748

That gives me 100,000, 10,000. That is a very large range, and this shows you why we need to use a logarithmic scale2758

because it would not be very practical to try to fit these wide ranges onto a scale that was just a linear scale.2771

Which should define our acids, which are bases and why?2781

Remember that acids increase the hydrogen ion concentration. Bases decrease the hydrogen ion concentration.2786

Let's look at this first one. This is showing the dissociation of a substance into...this should actually be 2 H+s + SO42-.2800

Since this is dissociating to form hydrogen ions, it is increasing the concentration of hydrogen ions to the solvent it is added to.2817

Therefore, this is an acid, and this is actually sulfuric acid; and it dissociates to form sulfates plus hydrogen ions.2829

HNO3 dissociates to form H+ + NO3-.2842

Again, since this is dissociating to form hydrogen ions, it is increasing the concentration of hydrogen ions, and therefore, it is an acid.2850

This is a strong acid, nitric acid, and it is dissociating to form hydrogen ions plus nitrate ions.2858

OK, here, we have NaOH dissociating to form Na+ + OH-.2875

Recall that another way to look at bases is that they increase concentration of hydroxide ions.2882

And then, the hydroxide ions bind the hydrogen ions to form water, and that, in turn, decreases the hydrogen ion concentration.2892

So, you can think of a base either as just something that decreases hydrogen ion concentration or that increases hydroxide ions.2902

Since this is increase in the concentration of OH-, it is a base, and this is a strong base, sodium hydroxide.2910

Sodium hydroxide disassociates into sodium and hydroxide.2920

Here, I have the arrows going both ways because these are weaker bases, so the reaction is not so far to the right.2928

Now, let's look at what is happening with this one.2937

It is dissociating to form...these are weaker acids or bases, we have to figure out2939

which one this is dissociating to form a hydrogen ion plus this other compound.2944

Increase hydrogen ion, I have an acid. This is a weak acid, it is acetic acid.2949

Acetic acid dissociates to hydrogen ions and compound called acetate.2955

Finally, Na2CO3 plus water dissociates to form two sodium ions plus this is bicarbonate and hydroxide.2962

So, I can see with this increase in the hydroxide, what I have is a base, and this is sodium bicarbonate, which is a weak base.2972

It dissociates to form sodium bicarbonate and a hydroxide.2987

Again, here we have an acid, sulfuric acid, another acid, nitric acid, and a base.2996

It is a strong base, sodium hydroxide; a weak acid, acetic acid; and a weak base, sodium bicarbonate.3003

And we define which are acids, which are bases and why in terms of what they do to the hydrogen ion concentration.3011

So, that concludes this lecture on the properties of water, and I will see you again soon.3018

Welcome to Educator.com.0000

In today's lesson, we are going to be discussing organic compounds, and living organisms are made up of organic compounds.0002

Organic compounds are compounds that contain carbon.0011

Compounds that do not contain carbon are known as inorganic compounds, and the field of study of organic compounds is called organic chemistry.0015

An example of an organic compound would be something such as methane/CH4, whereas water/H2O is considered inorganic.0026

Now, even though water is inorganic, it is obviously very important to biology and to life.0038

That is not to say that living organisms do not contain or need inorganic compounds, but they are mostly composed of organic compounds.0044

And that is going to be our focus of today's lecture.0051

A couple of exceptions though, although carbon monoxide and carbon dioxide contain carbon, these two are generally classed as inorganic.0056

There is a couple other exceptions as well, but these are the important ones that contain carbon but generally, scientists refer to as inorganic.0066

Alright, starting out with the basics, organic compounds have a carbon skeleton.0076

A carbon skeleton is a backbone of carbon, and then, the carbon atoms are bonded to other atoms.0085

This carbon skeleton could be various lengths.0093

It could be just a couple carbons long. It could be many carbons long.0099

It could be branched, so it could have carbons attached to this first linear section of carbons.0102

The atoms that are attached to carbon could be various atoms, but there are certain ones that are particularly important in biology0113

and that we are going to keep returning to, and those are hydrogen, oxygen, nitrogen, phosphorus and sulfur.0120

These are the ones we are going to focus on, although, of course, living organisms do contain other elements,0141

and use other elements such as calcium or magnesium, trace elements such as iron, that we discussed in the previous lecture.0147

But, for organic compounds, carbon plus these other five elements are the ones that you are going to see occur the most.0156

Now, carbon is a very versatile element, and that makes it an excellent basis for biological molecules.0164

Let's think back to the structure of carbon, and that will explain its versatility.0174

Recall that carbon has six electrons. That means that it has two in the first electron shell, and that shell is filled.0179

That shell only holds two.0191

It has four electrons in the second shell, so its valence shell contains four electrons.0192

And that leaves four empty spots, four more electrons to get to a total of eight for a full valence shell.0198

Therefore, it needs four electrons to fill its valence shell, and it can fill that shell in various ways.0204

It could form four single bonds with other elements such as, say, hydrogens here and then, the other carbon next to it.0217

So, that is one way it could fill. It is sharing four electron pairs with other atoms.0229

Another possibility is that it could form double bonds, so remember with CO2, carbon forms two double bonds,0236

one with one oxygen, one double bond with one oxygen molecule and oxygen atom, and then, another double bond with the second oxygen.0245

That, again, gives a total of four total shared electron pairs, and they will fill the valence shell of carbon.0254

This ability to share so many electron pairs gives carbon a lot of versatility,0260

and alas, just from a few different elements, a huge range of molecules that can be produced, and these molecules are the basis of life.0267

Hydrocarbons are molecules that consist only of carbon and hydrogen, so this would be an example of a hydrocarbon.0278

And the entire molecule is not necessarily a hydrocarbon. It could be a situation such as a protein.0299

There are actually other large biological molecule where there is a chain or just a section of hydrocarbons.0307

So, there can be a large biological molecule that has various different atoms on it, but one section of it is hydrocarbon.0313

And that hydrocarbon section is going to be non-polar.0321

Hydrocarbons are non-polar, and they form regions of molecules that are non-polar as well.0324

You could just have a hydrocarbon. You could have a larger molecule with just a hydrocarbon section on it.0331

We are going to focus on four classes of organic compounds today, actually two today and then, two in the next lecture.0340

but overall, four important classes, but before we do, we need to go on and discuss the concept of isomers.0348

Isomers are molecules that have the same molecular formula, but they differ in their structure; and there are three types of isomers.0355

This first type here is called structural isomers. The second type right down here shows geometric isomers.0364

And the third type is enantiomers, or these are sometimes called optical isomers.0376

Let's start with the structural isomers.0384

Well, first, to be isomers, they need to have the same molecular formula.0386

So, let's ensure that that is correct, 1, 2, 3, 4 carbons, so C4, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 hydrogens,0390

C4H10, 1, 2 , 3, 4, same here, it has 4 carbons, and 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 hydrogens.0400

These have the same molecular formula. They have the same atoms, same number, same ratio, but they are obviously different.0409

What makes them different is that they have different bonding partners.0416

These are arranged differently. They are covalently bonded to different atoms.0421

The difference between a pair of structural isomers is that one isomer has different bonding partners than the other,0427

OK, different bonding partners, same atoms arranged differently in terms of covalent bonding.0436

Looking at this molecule on the left, this is butane. This, right here, is butane, whereas this molecule is called isobutane.0448

And you will notice that butane just has this linear arrangement with the carbon skeleton, 1, 2, 3, 4 in a row.0463

whereas looking at isobutane, there are three carbons, and the middle carbon is covalently bonded to the fourth carbon.0474

And this difference in structure gives the molecules different properties.0481

The properties of a molecule are determined not just by the atoms that make it up but by the arrangement of those atoms.0485

That is an example of a structural isomer.0491

Now, let's look at geometric isomers.0495

I take a look at these and I see that "OK, I have 1, 2, 3, 4 carbon atoms, 3, 6, 7, 8 hydrogen- C4H8",0498

over here, 1, 2, 3, 4 carbon, 3 hydrogen, 6, 7, 8- same formula.0509

And then, I look, and each carbon is bonded to a carbon, and then, that carbon in turn the 3 hydrogens,0517

and then a hydrogen down here, and then, a CH3 group and a hydrogen and double bond at the carbon.0524

And if I look over here, it is the same thing.0529

Each carbon is double bonded to the other carbon and to the CH3 group and to a hydrogen.0531

They have the same bonding partners. They have the same atoms, but you can see that they are different.0540

And what makes them different is the spatial arrangement of the atoms around a double bond.0545

Double bonds are inflexible. The atoms cannot just rotate around that bond.0552

Now, if this were a single bond, this could actually rotate, and then, the hydrogen could flip up here.0557

The CH3 group can then go down here, and then, these would not actually be isomers.0562

But because this double bond is inflexible, these are, sort of, held in this position.0567

And you can see in this example, this molecule right here, these two CH3 groups are on the same side,0572

whereas here, the CH3 groups are on a different side, and what we call this is the cis isomer.0578

If the two groups are on the same side in the geometric isomer, that is the cis isomer,0584

the isomer where the two groups are in opposite sides is called the trans isomer.0590

Alright, so we have structural isomers. That was the first type of isomer.0596

Geometric, and then, the third is enantiomer or the other name for it is optical isomers.0600

And the name optical isomer helps to remember what it is because what it is is a mirror image.0607

Let's say that up here the blue is hydrogen, and then, maybe this brown is a carboxyl group, COOH.0617

In the center, we had a carbon bonded to a hydrogen, a carbon bonded to a carbon in turn bonded to these.0626

Maybe down here, I have what is called an amino group. This could be NH2 bonded and then, another atom, another group, say, CH3.0632

OK, now, the purple in the other molecule is, again, CH3, this brown, COH, and the green, NH2.0646

And if you look at these, they are mirror images, and they are not superimposable.0658

Because this is in 3-dimension, so maybe these two are coming out towards you, and it is similar to your left and right hands.0662

Your left and right hands are mirror images of each other, and they are not superimposable; and it is the same idea here.0671

And in fact, we call these left and right-handed molecules, and they are known often as L and D-enantiomers.0676

L stands for the Latin levo, which is left and then, D from the Latin dextro or right.0687

Optical isomers are left and right-handed forms of a molecule, and this difference is extremely important in science and biology.0702

For example, in pharmacology, it matters a lot sometimes which enantiomer you are working with.0711

There are some medications where one of the enantiomers is very effective, and the other is useless.0718

Or both may have a use, but they are different, or one may even be harmful.0724

Certain medications are a mix of the L and D-enantiomers, and one enantiomer is useful.0730

And the harmless one is in there as well, does not cause any problems but does not help either.0737

For Parkinson's disease, one treatment is a medication called L-Dopa.0742

L-Dopa is the L-enantiomer, and it is effective in treating Parkinson’s, whereas the D form of this molecule is not.0749

The next concept we are going to cover, before we get on to some0760

of the large molecules that you will be working with in biology, is that of functional groups.0763

You have already seen a couple of functional groups.0769

When I just wrote out the COOH, that is a carboxyl group. NH2 is an amino group.0771

Now, we are going to go ahead and treat this formally.0778

Groups of atoms that are especially important in determining a molecule's behavior are called functional groups.0780

And by determining its behavior, these are parts of the molecule that takes part in chemical reactions.0786

They determine what types of chemical reactions a molecule would participate in, and they also help to determine the shape or structure of the molecule.0795

And there are certain ones that you will see over and over, so you should become familiar with these and recognize them when you see them.0807

So, recall that hydrocarbons contain only carbon and hydrogen.0813

However, in many molecules, one or more of these hydrogens is replaced by a functional group.0821

Let's go over some of the common functional groups.0829

The first one is called an amino group, and as its name suggests, you will see these in amino acids.0832

This is NH2, and this line here indicates a bond, so this would be bonded to the carbon skeleton.0840

This is the functional group, and it is bonded to the carbon skeleton.0853

Sometimes, one of the carbons in the carbon skeleton is part of the functional group, and we will see that in a second.0855

But for now, the amino group, again, is found on amino acids, and it can actually act as a base.0861

It can pick up a hydrogen ion and become NH3+ in a solution.0868

OK, that is amino group.0877

The second group, which I already mentioned in the last slide, is a carboxyl group.0879

This carboxyl group is COOH, and this carbon could be part of a longer carbon skeleton.0884

Carboxyl groups are found in organic acids such as acetic acid. It has a carboxyl group.0894

Acetic acid is what is found in vinegar. It is what makes vinegar acidic.0902

In solution, the hydrogen ion could be lost, and then, this could become COO- and then a lost hydrogen.0907

These are also found on amino acids.0920

The next group, OH, is called a hydroxyl group. Hydroxyl groups are found on alcohols such as ethanol.0923

That ol-ending tells you it is an alcohol, and these are polar.0937

These are polar because of the preference of the electron pair to its oxygen, the more electronegative oxygen compared to the hydrogen.0946

The bond between the oxygen and the hydrogen, the electron pair favors more electronegative oxygen.0962

Right here, we have CH3 group. This is called a methyl group.0975

CH3 or a methyl group is found in what is called methylated compounds, and it could be attached to a carbon; or it could be attached to another atom, actually.0981

Here, we have what is called a carbonyl group.0992

And there is two subsets of how we name molecules containing these groups depending on where this group is within the larger molecule.0994

If, let's say, we had a carbonyl group right here embedded within the carbon skeleton, this would be called a ketone.1006

If the carbonyl group is in the middle within the carbon skeleton, it is called a ketone.1028

The other possibility is that this group is on the end. Here, the end carbon contains the carbonyl group, and this is what we call an aldehyde.1036

Again, there is two breakdowns for carbonyl groups: ketones, the carbonyl group is within the carbon skeleton. If it is on the end, it is an aldehyde.1054

An example here would be acetone. Aldehyde would build something like a formaldehyde.1064

Finally, we get to phosphate group, and you are going to see C phosphate groups throughout biology.1072

For example, cell membranes contain a phosphate group.1078

This is a phosphorus bonded to four oxygen atoms, and one of these oxygen atoms is bonded to the carbon skeleton.1083

You will notice that this is a charged molecule that to this oxygens have a negative charge, and therefore, it is hydrophilic.1093

Alright, now that we have talked about the basics of organic chemistry,1107

we are going to go on and talk about the four major classes of organic compounds that we are going to be discussing and focusing on in biology.1111

These four groups include carbohydrates, lipids, nucleic acids, and proteins.1121

In this lecture, in addition to covering the basics of organic compounds, we are going to be going over carbohydrates and lipids.1135

Nucleic acids and proteins are covered separately in the following lecture.1142

Carbohydrates are macromolecules. Macromolecules, just like their name, tells you macro and molecule are large molecules.1148

These are a vital source of energy for cells, and they have the molecular formula C, some X, H2O to Y,1158

and some multiple of H2O, various multiples of that.1171

What this is saying is that hydrogen and oxygen are found in the 2:1 ratio. That is what this is actually saying.1177

Hydrogen to oxygen, the ratio is 2:1.1185

As I mentioned, carbohydrates are an important energy source. They are found in many foods such as breads, rice, potatoes.1191

These are all rich in carbohydrates, and you will often hear people talk about simple carbs versus complex carbohydrates.1199

And we are going to talk about that as well, and that has to do with the structure of the carbohydrates.1205

Carbohydrates are sugars, and they can actually be categorized as monosaccharides, disaccharides and polysaccharides.1210

Starting out with just a simple situation, monosaccharides, mono meaning one, sacchar meaning sugar.1218

Monosaccharides have the formula CH2On, so some multiple of CH2O, some multiple of that, where n is usually either 3, 5 or 6.1228

If n is 3, you will end up with C3H6O3, and if you have a 3-carbon sugar like this, it is known as a trios. 3-carbon sugar is a trios.1249

A 5-carbon sugar is called a pentose, and a 6-carbon sugar is called a hexose sugar.1263

Let's go ahead and look at a couple different types of monosaccharides: glucose and fructose.1272

Glucose is the main form in which you will find sugar stored in animals. Fructose is the type of sugar that you will find in fruits.1278

Glucose is produced by plants via photosynthesis, and then, this can be broken down by cells to release the energy to fuel various cellular processes.1289

Glucose and fructose have the molecular formula C6H12O6, and you should recognize this.1298

This formula will come up, and you should recognize it as a formula for this particular type of monosaccharide, which is a hexose sugar.1304

Let's go ahead and look at the two forms.1314

You will see that there is a linear form and a circular form, and the reason for this is that in aqueous solution, sugars often exist in their ring form.1317

So, this is the same sugar. These two are the same, and these two are the same, but this is just the linear form.1328

And then, in aqueous solution, it would form this ring, so you will often see these molecules written in their ring form.1333

And to keep track of things, we number the carbons, and we start at the top: 1, 2, 3, 4, 5, 6.1341

And then, we can refer to groups on the different carbons based on their number.1348

2 is here, 3. This is 4, 5 and 6, so these are 6-carbon sugars. These are hexoses.1355

Now, when this turns into a ring, we need to keep track and see where all these carbons go, and again, we number them 1, 2, 3, 4, 5 and 6.1364

And we can do the same over here with fructose.1378

All it is, is that this forms a ring, and you could see the 6 sticking up right here, same thing with fructose.1382

Now, another thing that I mentioned before is the location of the carbonyl group, this C double bonded to O.1396

Looking first at glucose, you will see that this C double bond OH right here, this carbonyl group is on the end.1406

And recall that, when it is on the end, we call that an aldehyde, so this is actually what we call an aldehyde sugar or an aldose sugar. Glucose is an aldose sugar.1413

Fructose, a carbonyl group is here. It is embedded within the carbon skeleton, so this is what we call a ketose or ketone sugar so ketose sugar.1427

And again, that is based on the location of this C double bond O: on the end in glucose, embedded within the carbon skeleton on fructose.1440

Those were monosaccharides. Monosaccharide means that there is just one sugar.1453

There is just one subunit.1460

Monosaccharides can join together to form a disaccharide. Disaccharide, just like the name suggests, two sugar subunits.1462

These are both known as simple sugars.1474

If you have more than two subunits, it is called a polysaccharides, and those are complex carbohydrates.1480

So, simple carbs or simple carbohydrates, simple sugars and then, polysaccharides are known as complex carbohydrates.1487

The formation of disaccharides or polysaccharides occurs when two monosaccharides join through what is called a dehydration reaction.1499

Dehydration means you lose water, and that is exactly what happens here.1512

If you looked at just two glucose molecules, this was a single glucose molecule and then, a second glucose molecule,1518

they bond together through this dehydration or condensation reaction.1527

Before they were bonded together, what you would have had is on this molecule and a hydrogen up here, the hydroxyl group right here.1531

And each of these corners/points, that is a carbon.1545

This is a carbon. This is a carbon.1549

This is a carbon. This is a carbon.1551

For simplicity, we often do not write this out.1553

In the ring form, it is just convention that each of these is a carbon.1555

You have a carbon here, and it is bonded to a carbon, the oxygen next to it, the next carbon, the hydrogen and this hydroxyl group.1560

The same thing for the other glucose, so there was an adjacent glucose, free, not bonded to the next glucose - this is before the reaction - that looks like this.1574

Then, what happened is one of these glucose molecules - this was glucose, free glucose, monosaccharide, this is glucose - one of these loses an OH.1586

The other loses a hydrogen, so it loses HOH or H2O, in other words, water. That is why it is called a dehydration reaction.1599

With this gone, this OH, and this hydrogen gone, you are left with these two bonded together via this remaining oxygen, and that is what you see here.1612

One of these has lost an OH, a hydroxyl group. The other has lost a hydrogen, and that remaining oxygen, then, links to adjacent sugar molecules together.1623

This bond is called a glycosidic bond. Adjacent sugars are held together by a glycosidic bond formed through a condensation reaction.1634

And that forms, which has two subunits. They are both glucose, and this is a disaccharide.1646

It is also known as a simple carbohydrate or simple sugar.1653

Lactose would be another example. This is a sugar that is found in milk.1659

And this is formed between glycosidic linkages between one molecule of glucose and a second molecule of another sugar called galactose.1663

Sometimes, you will hear people talk about lactose intolerant. They are not able to have dairy products like milk or cheese.1674

And the reason is, they lack an enzyme called lactase.1683

When we talk about enzymes, you will see that ase-ending tells you it is an enzyme, and here ose tells me this is a sugar.1689

So, lactase is the enzyme that breaks down lactose, and if somebody is lacking this, they do not have very much of this,1696

they are not able to break down this sugar, and that causes them to have gastrointestinal symptoms when they have dairy products.1701

OK, what we started out with down here with the maltose was glucose, C6H12O6, but we actually had two of those.1712

Actually let's move over here where there is a bit more room, so C6H12O6.1732

But, we actually had two of these, and these came together to form C12H22O11 plus one molecule of water.1739

So, 2 x 6, that gives you 12 carbons. 2 x 12 is 24, and we have 22 here in this disaccharide,1753

then, the other two in the water molecule that was lost in the dehydration reaction, and then, 2 x 6 is 12.1760

We have 11 oxygens here within the disaccharide, and then, 1 oxygen, again, lost as part of that water molecule.1768

Now, sugars in plants and animals and organisms are usually stored in more complex forms than just monosaccharides and disaccharides.1776

And then, they are broken down as needed to provide energy.1785

The formation of the glycosidic bond is through what is called this dehydration or condensation reaction.1790

The opposite is hydrolysis. Hydrolysis comes from hydro meaning water, and then, lysis meaning to break.1799

To break the glycosidic bond, hydrolysis reaction occurs, and what happens is it adds water.1812

Water is added to the bond, and it releases this bond; so that you, then, have two glucose molecules back.1820

A maltose is formed through the dehydration reaction forming glycosidic bond.1829

And then, hydrolysis can add water and turn these into two separate glucose molecules.1835

Sugar are actually stored in more complex forms, and those forms would be starch usually in plants.1842

And then, in animals, what you will see is glycogen. Sugar is stored in the form of glycogen.1852

Looking at this starch molecule, you will see that it is much more complex than the disaccharide, and it is, in fact, a complex carbohydrate.1862

This is formed through glycosidic bonds that are joining more of these monosaccharide subunits and joining them here in a branched form.1874

Looking at starch, there is a couple different kinds of starch.1885

One type is amylose. Another type, which is shown here, is amylopectin.1889

This is amylopectin, and you will see that it is branched.1898

Another thing to note is that the 3-dimensional structure of starch is helical.1901

We call starch and glycogen, we call these polymers, so when there is a chain formed from similar identical subunits, these are known as polymers.1907

A bunch of subunits of glucose join together. They can be a linear form and then, form a helix, that is amylose.1919

It can branch off and form amylopectin.1927

Glycogen is even more highly branched than amylopectin. Again, it is a form of polysaccharide.1930

It is a way of storing sugar in animals, and glycogen and starch can both be broken down through hydrolysis to release the energy as needed.1938

Glycogen is found primarily in the liver and in muscle cells.1948

Sugars are used for quick energy, so they are rapidly available; but they are also rapidly depleted.1954

And that is why we have other forms of energy store such as fats, which we will talk about shortly, and proteins.1961

In addition to being forms of energy, carbohydrates also have a structural function.1970

I was focusing here on starch and glycogen and the glucose subunits as forms of energy, and they are obviously important for that.1978

Carbohydrates are also used to form structures in plants and animals.1990

If starch is an energy form, glycogen is an energy form, what are the structural forms?1997

Well, plants contain cellulose, and we will go into detail about cellulose in the plant lecture.2001

But for now, you should just know that this is a form of carbohydrate that is found in the cell walls of plants.2010

Plants do not have skeletons obviously, so for support and for protection, instead, they have cell walls.2015

And cellulose is a polymer made of glucose subunits that is the primary component of the cell wall of plants. It is different, though, than starch.2023

It is not the same as starch. It is not the same as glycogen.2031

It has a different 3-dimensional structure.2035

Cellulose actually are glucose monomers that hydrogen bond, and they form what is called microfibrals.2038

It is a fibrous type, more of a fiber-like or cable-like structure, a microfibral.2045

Humans cannot digest cellulose, so what we call roughage is a part of the plant that passes through the human GI tract undigested.2054

And that is the cellulose, so especially with raw fruits or raw vegetables, apples, figs, carrots or anything, these contain roughage.2064

And although, they are not digested, they are important for the GI tract because when we call them roughage, it is actually a pretty accurate name.2073

It actually scrapes against the walls of the intestine, and that stimulates mucus secretions from the cells in the intestine.2080

So, even though cellulose is not digestible, it is an important part of the human diet.2088

OK, structural forms of carbohydrates: one is cellulose, another is chitin.2094

Chitin is found in the cell walls of fungi such as mushrooms, and it also makes up the exoskeleton of arthropods such as crustaceans, also insects.2100

This is found in exoskeletons, and it is also found in the cell wall of fungi.2112

Again, we will revisit this all in detail in later lectures, but just give me some examples now to make this more concrete.2117

Two functions of carbohydrates: one is as an energy store in form such as glucose, maltose, lactose, starches, glycogen.2125

The second: structural functions, and this could be cellulose found in the cell walls of plants,2136

chitin, which is found in the cell walls of fungi as well as the exoskeletons.2141

Alright, carbohydrates were the first class of large biological molecule.2147

The second group of large biological molecules that we will be discussing is lipids, and these are actually a diverse group of molecules.2153

But they are classed together because they are all non-polar or hydrophobic.2160

Example of lipids are fats, oils, phospholipids and steroids as well as waxes.2165

We are going to be focusing on fats, phospholipids and steroids because these are the most important in terms of biology.2170

If you glance down here at a typical fat, this is a triglyceride or fat, you will see that it has this large regions of hydrocarbons.2179

These long hydrocarbon chains are regions that are non-polar.2189

I mentioned that earlier in this lecture that hydrocarbons are non-polar, and non-polar molecules contain regions of hydrocarbons.2194

Let's go ahead and see how a triglyceride molecule is built.2204

It is built from one glycerol and three fatty acid molecules, so one glycerol plus three fatty acid molecules equals one triglyceride.2208

Glycerol is an alcohol, and each glycerol, then, bonds with the three fatty acids.2219

And you can see where these are linked, if you look first at the glycerol molecule and then, this OH group.2230

And then, you will see CH2, O, and then, it is bonded to the first fatty acid, the second fatty acid and the third fatty acid.2242

And this is, again, a dehydration reaction.2252

If you look here, you will see OH and then, C double bond O, OH.2255

I look over here, there is two oxygens and this carbon and a carbon here.2264

What has happened is through the dehydration reaction, two hydrogens and one oxygen had been lost.2271

The dehydration reaction, loss of H2O and then, the glycerol molecule ends up bonded to the fatty acid via this oxygen.2281

This type of linkage is called an ester linkage. As ester linkage is a bond between a hydroxyl group and a carboxyl group.2294

A bond between these two type of functional groups that is formed is called an ester linkage.2311

Here, we have three ester linkages between one glycerol and three fatty acid molecules.2315

As you can see the formation of that between these two molecules to here, adding two more groups gives you the triglyceride2322

and the tri meaning three, so three fatty acid chains on the one glycerol molecule.2331

Fats can be divided up into two different categories.2338

And you have probably heard these categories or read them on nutrition labels: saturated and unsaturated.2340

When we say that a fat is saturated, we mean that the carbons are saturated with hydrogens. Think of it that way.2355

Another way of looking at it is there are no double bonds between the carbons.2364

This is a saturated fat shown here because all the carbons are held together by single bonds, and each carbon is saturated with hydrogens.2372

It is holding as many hydrogens as it can. It is bonded to as many hydrogens as it can be.2382

Unsaturated, there is one or more double bonds between the carbons.2387

For example, if I inserted a double bond here, I would have to, then, get rid of this hydrogen.2395

This carbon is no longer fully saturated with hydrogen. It has a double bond to the adjacent carbon.2402

You will often hear people say "oh, saturated fats are the bad ones, and unsaturated are the good ones".2414

Let's talk about some differences between these two types of fats.2419

Saturated fats have no double bonds, and they often come from animals. They are animal fats.2424

They are solid at room temperature, and the molecules that comprise them pack together tightly.2434

And that has to do with the fact that they are just single bonds. An example would be butter.2445

Unsaturated fats usually come from plants. They are liquid at room temperature, and they do not pack together as tightly.2454

The reason for that is this double bond creates a kink.2467

You will often see the fatty acid tails, so if this is the glycerol, you will sometimes see these fatty acid tails shown as zigzags just like this.2471

That is their structure and so on.2492

Now, when there is a double bond, it introduces an even larger kink, so it would go out to the side like that.2501

For example, this might be a saturated fat, and then, if there is a double bond, it actually kinks the molecule so that it is not just a straight tail like this.2508

And you can see that if this is kinked, these could not pack together as tightly. They could not pack together with adjacent fat molecules.2518

This double bond causes the kink in the fatty acid tails that does not allow them to pack together as tightly.2526

And that is also why they stay liquid at room temperature. They do not solidify because they are not packed together as well.2532

A diet that is high in saturated fat increases a person's risk of atherosclerosis.2540

An atherosclerosis is the formation of plaques in the blood vessels, and these plaques decrease the flow of blood to the vessels, and it can result in heart disease.2544

Often, unsaturated fats are thought of as the healthier fats. An example would be canola oil.2554

Canola oil is mostly unsaturated fat, whereas butter is mostly saturated fat.2561

Now, fats are a way for organisms to store energy. I mentioned that animals can store glucose as glycogen, and then, they can break it down.2568

But that gets rapidly depleted. For longer term storage, a very efficient way to store energy is as fat.2578

Adipose tissue serves as a way to store energy, and it also serves as insulation and protection.2585

These are just some functions of lipids. Another function of lipids in addition to fats would be to form phospholipid.2594

We talked about one type of lipid, which is fat. The second type we are going to talk about is phospholipids.2604

Cell membranes are made up of phospholipids, and let's go ahead and look at the structure.2610

Here, we have the glycerol molecule again, and we have fatty acid tails; but this time, we only have two.2615

Instead, this third carbon, instead of being bonded to a third fatty acid, it is bonded to a phosphate group.2629

This phosphate can, in turn, be bonded to another functional group, and that will determine which type of phospholipid that you have.2640

But the basics for phospholipids are glycerol, two fatty acid tails and a phosphate group.2650

The phosphate plus the glycerol, this region is hydrophilic, so we say that phospholipids have a hydrophilic head.2658

And then, we look at the fatty acid tails, and we say that they have hydrophobic tails.2669

Because there is one section that is hydrophilic and another that is hydrophobic, we say that this molecule is amphipathic.2681

An amphipathic molecule has a hydrophobic region and a hydrophilic region.2687

Because of this amphipathic nature, phospholipids self-aggregate in the bilayers, and they do this in order to shield these hydrophobic portions from water.2708

What you will end up with is phospholipid bilayers where the hydrophilic heads face outward, and the hydrophobic tails are sequestered inside.2720

This is the hydrophobic portion, and it is sequestered inside from the water.2731

The interesting thing about this is, well, the structure is that it can serve as a barrier.2736

And it does serve as a barrier so that the cell membrane only allows certain substances to pass through.2744

And, in particular, hydrophobic substances will pass much more easily through the cell membrane because of this phospholipid bilayer's non-polar central region.2749

Hydrophobic molecules tend to pass through the cell membrane more easily than the hydrophilic molecules.2760

This is an introduction of phospholipids, and we are going to do a lecture later on in the course on cell membranes2765

and talk more about the structure, as well as about substances that pass through the cell membrane easily and those that do not.2771

Alright, so far, we have discussed fats and phospholipids, which are both types of lipids.2780

The third type of lipid we are going to discuss is steroids. Steroids are lipids that contain a carbon skeleton of four fused rings.2785

This basic ring structure is called cholesterol, and it is the building block for other steroids.2794

Hormones are substances that allow cells to communicate with and affect cells a distance away.2806

For example, a hormone would be estrogen or testosterone. These are both hormones.2813

Many hormones are steroids. These two are steroids, so estrogen and testosterone are examples of steroid hormones.2824

That means that they have this basic four fused ring structure, but there are different functional groups attached.2834

The bonding is a little bit different, so alterations are made to these that give each one a unique structure and very different function and properties.2841

And if you think about it, you can see that this is going to be pretty non-polar. It is going to be hydrophobic.2851

And that is actually very helpful for a hormone because it allows them to pass into the cell.2856

Again, we are going to revisit this topic later on when we talk about cell membranes and cell communication.2862

But for right now, you just need to know that hormones are often steroids, and that steroids are based on a cholesterol ring; and they are non-polar.2867

Alright, today, we have discussed two of the four classes of large biomolecules.2876

We have discussed carbohydrates and lipids, and we are going to continue on in the next lecture to talk about nucleic acids and proteins.2882

But before we do, let's do a few examples to reinforce your knowledge.2889

Example one: what type of isomer is each of the pairs of molecules shown below?2894

Remember that isomers have the same molecular formula, so let's just double check and see that that is true.2899

I have two carbons here, two bromines and two hydrogens.2906

On the other molecule, I also have two carbons, two bromines, two hydrogens- same molecular formula.2911

The first type of isomer is a structural isomer, so let's see if they have the same bonding partners.2918

Each carbon is double bonded to another carbon on both of these, and then, each carbon is bonded to bromine and hydrogen- bromine, hydrogen.2925

Same here, but they are not the same geometrically. They differ in their spatial arrangement.2933

These are not structural isomers since they have the same bonding partners. In fact, they are geometric isomers, and one clue to this is the double bond.2939

This inflexible double bond holds these molecules in a certain conformation where the two bromine molecules are on one side in this isomer.2949

This would be the cis isomer, and they are in the opposite sides in the other isomer, and this is known as the trans isomer.2958

That is my first set of molecules. The second set, I am going to double check and make sure that the molecular formulas are the same:2965

1, 2, 3 carbons, 1, 2, 3, 4, 5, 6, 7, 8 hydrogens, 3 carbons, 8 hydrogens, 1 oxygen.2971

Over here, 1, 2, 3 carbons, 1, 2, 3, 4, 5, 6, 7, 8 hydrogens, 1 oxygen, so these have the same molecular formula.2981

Next thing to check: are the bonding partners the same?2993

Here, I have a linear arrangement of carbon, carbon, carbon and then, oxygen.2996

Here, I have the three carbons, but instead of the oxygen being bonded to a carbon on the end, the oxygen is bonded to a middle carbon.3002

Therefore, the covalent bonding is different, and these are, in fact, structural isomers.3011

These are both forms of propranolol. This is actually propyl alcohol, while this one is isopropyl alcohol.3020

And again, these different isomers are going to have different properties.3033

The first example was geometric isomer. The second is an example of structural isomers.3040

Second example: identify the functional groups on the molecules below.3046

Let's go ahead and just look at the linear. This shows glucose and both its forms.3052

We can look at it in either, but I am going to look at the linear; and this is actually an amino acid.3055

Let's look at all three of these and just see what we can identify. One thing that we can identify here is a hydroxyl group.3063

Here, on the end, this has a carbonyl group, and remember that when it is on the end like this, we often call it aldehyde.3077

If it was in the middle, we would have called it ketone group.3085

Over here, I have COOH right here, so this group is a carboxyl.3093

The carbonyl is C double bond OH.3104

I have identified hydroxyl, carbonyl, carboxyl, and then, I have an NH2 here. NH2 is called an amino group.3108

What do I have here? CH3, I have two of these, and these are methyl groups, OK?3121

Here are some of the various function groups that I have identified: carbonyl, particularly an aldehyde, hydroxyl, amino, carboxyl and methyl.3131

Example three: the structural formula for galactose, a sugar, is shown below.3146

Based on the number of carbons, what type of sugar is galactose. Is it a ketose sugar or an aldehyde sugar?3152

OK, this is galactose, 1, 2, 3, 4, 5, 6 carbons. Therefore, this is a hexose sugar.3158

To determine if it is a ketose or aldehyde sugar, I need to look for the carbonyl group, and that is right here.3169

It is on the end carbon. Therefore, this is an aldehyde sugar.3175

So, galactose is a hexose sugar, and it is an aldehyde sugar.3182

Example four: what class of molecules does this molecule belong to? Why?3189

Well, you probably immediately notice this characteristic structure of four fused rings, and this molecule, therefore, is based on cholesterol.3195

Therefore, it is a steroid.3206

Notice, though, that the bonding, the functional groups, are a bit different than on cholesterol.3209

And in fact, this happens to be estradiol, which is a form of estrogen.3215

You can see that change in the structure just a bit gives it very different function and unique properties.3219

That concludes this lecture on organic compounds at Educator.com, and I will see you again next time.3227

Welcome to Educator.com.0000

We are going to continue our discussion of large biological molecules with a lesson on nucleic acids and proteins.0002

In the previous lecture, we talked about two other classes of large biological molecules- carbohydrates and lipids.0010

I also introduced some basic sub-organic chemistry there, so if you have not watched that lecture yet,0017

and you are not familiar with organic chemistry, you may want to watch at least the first part of that before going on to this.0022

There are two types of nucleic acids: DNA/deoxyribonucleic acid and ribonucleic acid.0030

DNA contains an organism's genetic information, and that information is passed on from parents to offspring.0037

DNA codes for proteins.0045

In the molecular biology section, we will talk about how DNA is synthesized, how the DNA is transcribed into RNA, and how that RNA is translated into a protein.0048

Right now, we are just focusing on the structure of both DNA and RNA.0062

DNA is made up of nucleotides. These are the building blocks for the DNA molecules.0068

RNA, same thing, it is made up of monomers of nucleotides, so let's go ahead and look at the nucleotide structure.0078

There are three parts: there is a sugar; there is a nitrogenous space; and there is a phosphate group.0087

In both DNA and RNA, the sugars are 5-carbon sugars, so these are pentoses.0096

However, the sugar in DNA is deoxyribose, whereas RNA contains ribose, so the name explains the difference.0102

Deoxyribose is missing one of the oxygens, so ribose has a hydroxyl group here, whereas DNA just has a hydrogen.0111

That is one difference between DNA and RNA although their fundamental structure is the same.0124

DNA and RNA both have nitrogenous bases attached to the sugars, and there are five different types of nitrogenous spaces that we will look at in the next slide.0131

If you just consider the nitrogenous base plus the sugar in either DNA or RNA, that is called the nucleoside.0147

With the phosphate group added, you have a nucleotide.0158

These nucleotides are the monomers from which the larger DNA or RNA molecule are formed.0168

Here, are shown the five different nitrogenous bases, and they can be classed into two groups.0182

These first two are more complex. They have a 6-membered ring fused to a 5-membered ring, and these are known as purines.0192

These top two are purines, and there are two.0202

Adenine, it is often known by its abbreviation A and quinine known by just the letter G.0205

Here, below in this row, are the pyrimidines. They are based on this 6-membered ring.0213

And these are rings that contain carbon and nitrogen, and there are three pyrimidines: cytosine, thiamine and uracil.0221

One important thing to know is that thiamine is found only in DNA, whereas uracil is found only in RNA.0231

In lieu of thiamine, RNA has uracil, otherwise, DNA and RNA have the same nitrogenous bases.0245

A, G and C are found in both DNA and RNA, thiamine only in DNA, uracil only in RNA.0255

One thing also to keep in mind as you are looking at structures of RNA and DNA is that in order to distinguish the carbons0262

on the nitrogenous bases from the atoms on a sugar, the atoms on the sugars - ribose and deoxyribose - have a prime after them.0272

So, we will sometimes be referring to the 2-prime or the 3-prime carbon, and those refer to the different atoms on the sugar.0282

These prime means that we are talking about the atom on the sugar versus an atom on these nitrogenous bases.0292

Nucleotides join to form polymers that consist of a sugar phosphate backbone with the attached nitrogenous bases.0301

One nucleotide is linked to the next nucleotide to form what is called a polynucleotide.0310

The monomers are the nucleotides, and they join to form polynucleotides; and that is usually what we are talking about when we talk about DNA and RNA.0317

The linkage that attaches these is known as a phosphodiester linkage.0326

Remember, when you just looked at the monomers, each one of them had a sugar, a nitrogenous base and a phosphate group.0342

And the phosphate groups serve as the linkage between one monomer and the next monomer.0348

We are going to talk about this synthesis in detail in the molecular biology lecture, but for right now, you should be aware that there is a directionality to DNA.0357

And we discussed DNA and RNA as having 5-prime ends and 3-prime ends.0365

The 5-prime carbon on what we call the 5-prime end of the polynucleotide has a phosphate group attached, so this is the 5-prime end.0375

There is a phosphate group attached to the 5-prime carbon.0385

This end is called the 3-prime end, so there is this three hydroxyl group.0392

Here, we have this phosphate group to 5-prime end, and then, we have the hydroxyl group attached to a 3-prime carbon on the 3-prime end.0400

This directionality is very important because synthesis of DNA always occurs 5-prime to 3-prime.0409

And again, we will get into the details of that later, but right now, you should just know the basics that there is a 5-prime end. There is a 3-prime end.0417

Two adjacent nucleotides are linked via a phosphodiester linkage.0424

And you should also be aware that this section, the sugar and the phosphate group, are known as the sugar-phosphate backbone,0430

so, sugar-phosphate backbone right here and then, attached nitrogenous bases.0442

The order of these nitrogenous bases is the genetic code.0452

You could have a strand of DNA that may have a nitrogenous base A attached. The next one is G, then another G, C, T.0458

And it is these bases, it is the order of those bases, that encodes the information to make a protein.0468

And it is this information, this order of the bases, that is passed along from parent to offspring.0475

DNA is found in a double helix structure. This double helix structure is formed by two complimentary strands.0483

These strands are also anti-parallel, so what do we mean by anti-parallel? Well, it has to do with that directionality.0491

Let's say that this is the 5-prime end of one of these pieces of DNA, and we follow this down; and it is going to end here at the 3-prime end.0501

The other strand is going to have the opposite orientation where it starts with the 3-prime end up here and then, ends at the 5-prime end down here.0512

So, we say that these two strands are anti-parallel. They are complimentary, and they are anti-parallel.0522

The 5-prime to 3-prime versus 3-prime to 5-prime explains the anti-parallel.0532

What does complimentary mean? Well that has to do with what is called base pairing.0538

Remember that in DNA, there is no uracil used. We have A, G, C and T.0542

Adenine pairs with thiamine, and this would be called a base pair; and G/guanine pairs with cytosine.0553

Here is a sugar-phosphate backbone shown with a purple.0572

And then, the nitrogenous bases A, G, C and T actually stick inward towards the center, towards the middle of this double helix.0575

This double helix structure was actually a famous discovery by Watson and Crick in the 1950s.0594

And, we have the sugar-phosphate backbone, and then, let's say this nitrogenous base here is A and T, C, G, A, T.0600

Since A pairs with T, this complimentary strand is going to have a T.0619

T pairs with A. The complimentary strand will have a an A.0624

C is going to pair up with G, so you are going to have a G here.0627

G, C, A pairs up with T. T pairs up with A and so on.0635

Complimentary refers to the fact that the base pair on the second strand matches with the base on the first strand.0643

Now, hydrogen bonding occurs between these base pairs, and that is what holds this helix in its structure.0655

And you will notice up here that I showed three dotted lines between G and C, whereas there is only two dotted lines between A and T.0663

And that is because A-T forms two hydrogen bonds with each other, whereas G and C form three hydrogen bonds with each other.0671

OK, important place to remember is that DNA is a 5-prime end, a 3-prime end.0681

Nucleotides are linked by a phosphodiester linkage.0686

Their structure is such that there is a DNA double helix that is formed between two complimentary anti-parallel strands.0691

Each strand is paired so that it has a matching base pair.0702

A always pairs with T. G always pairs with C.0709

And these nitrogenous bases, these base pairs, form hydrogen bonds that keep this double helix structure in place.0714

RNA is single-stranded.0723

In biology, form follows function, and you will see how this double helix is very important0731

in the synthesis of DNA and in producing DNA that has as few mistakes as possible, so that genetic mistakes or mutations are not introduced.0735

We will revisit this double helix structure later on with a focus on DNA synthesis, transcription and translation.0744

The next large biomolecule that we will talk about is proteins.0755

Amino acids are the building blocks of proteins, and these join to form polypeptides.0759

So, remember that DNA contain genes, and these genes encode proteins.0765

Proteins are extremely important to living organisms because they make up structural elements such as our muscles.0773

They facilitate reactions in the form of enzymes, which we will discuss later.0781

They are involved in cell signalling. They are involved in cell growth and the repair of cells, so proteins are fundamental to life.0785

There are twenty main or common amino acids.0792

You do not have to know each of these. You just need to know the general structure of amino acids and some different classifications of the amino acids.0797

Let's look at just a generalized amino acid. You are going to see that it has certain groups.0805

Here, it has an amino group. On the other side, it has a carboxyl group.0810

In the center is a carbon atom, so bonded to the carboxyl group, the amino group, a hydrogen and then, what we call an R-group.0821

The R-groups are different, so each of the twenty amino acids has a different R-group.0830

It could be as simple as just hydrogen. That would be just glycine, structurally the simplest amino acid.0836

Or it could have more complex functional group like shown here with asparagine or even more complex than that.0839

You might see amino acids also written instead of NH2, you might see this shown as NH3+ and the carboxyl group as COO-.0852

And that is because in water, the amino group picks up a hydrogen ion and, therefore, acts as a base.0862

And that carboxyl group loses a hydrogen ion and, therefore, acts as an acid.0871

You are also going to notice that there are 3-letter abbreviations for the amino acids, so you might see instead of asparagine written out, Asn.0880

Or for example, leucine is another amino acid that is abbreviated as Leu and glutamine, Gln.0888

There are also 1-letter abbreviations for the amino acids.0896

Let's talk a little bit more about these side chains. The side chains can be grouped such that they are non-polar, they are polar, they are acidic, or they are basic.0900

First, let's just talk about non-polar.0926

Glycine has an R-group that is just a hydrogen atom. That is going to be an example of a non-polar amino acid.0929

A polar amino acid might have, for example, hydroxyl groups on it or some other polar functional groups.0941

Asparagine is actually considered a polar amino acid, so this one is polar.0950

Acidic and basic are a little bit more complicated.0957

When we talk about acidic or basic amino acids, we are not talking about the amino group here or the carboxyl group here.0960

We are talking about the R-group or the side chain.0966

If you think about it, in a solution, this is going to pick up a hydrogen ion. This is going to lose one.0970

They are going to essentially neutralize each other.0974

So, the amino acids overall, in the different forms that they are in in solution. If they are not, it is going to be that they are neutral.0976

However, if there is a carboxyl group on the side chain, if the side chain has a carboxyl group, then, you would have an acidic amino acid.0985

If the side chain contains an amino group, then, you would have a basic amino acid.0998

Again, we are not looking at this. When we talk about polar or non-polar amino acids, we are talking just about what is going on with the side chain.1008

I want to point this out. This is a bit of an exception.1015

Glutamine and asparagine are both polar. They are not basic.1020

Even though you see this NH2 here, and you might think "oh, an amino group".1027

This particular construction, where you have C double bonded to O, linked to NH2, is something called an amide group.1030

And this is a bit different. It is not actually basic.1039

If you had this NH2 but it was not linked to the C double bond O, then, I would say "OK, you have a basic amino acid".1044

But this particular group together actually is not a basic side chain.1049

Glutamine has this group. Asparagine has this group.1055

These two are classed as polar, not as basic.1058

Aspartic acid is a good example of an acidic amino acid. The side chain contains COOH, this carboxyl group and that cellular pH.1063

This becomes ionized to COO-, and therefore, this is an acidic amino acid. It tells you so in its name.1079

OK, we talked about amino acids. These are the building blocks for proteins.1089

Amino acids can be joined together to the formation that is called a peptide bond.1095

A peptide bond is yet another dehydration reaction.1101

We discussed that in previous lecture where a dehydration reaction is a reaction where water is removed, so we lose a water.1104

Recall that the basic structure of an amino acid would be NH2, central carbon, an R-group, hydrogen, and then, we have this carboxyl group, COOH.1115

An adjacent amino acid would have the same structure, so now, we are just going to do COOH over here, R here.1139

Here, we have the NH2, and here we have H; so, let's write this as NHH1150

This peptide formation, again, is through a dehydration reaction, so water is going to be lost.1163

So, if an OH is removed from here, and then, H is removed from here, you are going to end up with H2O removed.1169

And that will leave this CO, which is this, becomes double bond, and this nitrogen, which is here, bonded together.1179

This carbon from the carboxyl group bonds to the nitrogen from the amino group, and water is lost.1189

Again, COOH and NH2, loss of an OH group from the carboxyl, a hydrogen from the amino group, leaving behind C double bonded to O.1195

And then, the C bonds to the nitrogen and then adjacent amino acid forming a peptide bond.1206

What is shown here is a dipeptide. It is two amino acids.1213

Three or more amino acids are a polypeptide chain, and a polypeptide chain can be very short, just a few amino acids.1216

It can be a thousand amino acids long.1223

The primary structure of a protein is the amino acid sequence of its polypeptide chain.1226

There are multiple levels of structure in a protein. There are three to four depending on the type of protein: primary, secondary, tertiary and quaternary.1233

The primary structure is just the order of the amino acids if it is leucine and glycine, glutamic acid, then another asparagine, another asparagine.1242

That would be giving the primary structure of the protein.1252

Now, polypeptides are not the same as proteins. Polypeptides are just chains of amino acids.1259

They are in a particular order, but if they are unfolded, they are just chains- they are polypeptides.1268

In order to actually be protein, a polypeptide chain or chains - sometimes there is more than one chain in the protein - need to be folded1273

in a unique 3-dimensional conformation, then, that is a protein.1280

Once you just have bunch of amino acids linked, it is not a protein yet. It is a protein once it is folded.1285

The primary structure is actually what determines this folding, although nobody is quite sure how.1291

And the primary structure of a protein was first elucidated by Fred Sanger at Cambridge, and he and his lab actually sequenced insulin.1298

Remember that insulin is a hormone secreted by the pancreas, and it is vital in controlling glucose levels in the bloodstream.1308

Without enough insulin, a person becomes diabetic.1315

Another medical example of the importance of the primary structure of protein is the disease sickle-cell anemia.1317

This disease is caused by the substitution of a single amino acid- valine.1327

Instead of valine, it is actually, valine is substituted for glutamic acid, so valine substitution.1334

That change of that one amino acid to a different amino acid causes problems in the structure of hemoglobin.1347

Hemoglobin is found in red blood cells. It carries oxygen.1355

The structure of the hemoglobin is abnormal in people with sickle-cell anemia, and the result is that it actually causes the red blood cells to form a sickle shape.1359

And those sickle-shaped cells tend to clump up.1367

Red blood cells are normally a biconcave disk. They move nicely through even small vessels like capillaries.1373

With sickle-cell anemia, these cells form a sickle shape. They clump up, and that causes poor circulation to various parts of the body and symptoms.1379

The primary structure of a protein is very important in determining the secondary and tertiary structure and the function of the protein.1388

So, we went to this first level of structure. Let's go into more detail about the other levels1397

The secondary structure of a protein is the result of hydrogen bonding between different regions of the polypeptide backbone.1402

When I say polypeptide backbone, that means not the side chain. It means the other parts.1409

The two main protein secondary structures are alpha-helices and beta-pleated sheets, so let's go back to how these are formed.1415

There are certain regions on a polypeptide strand that are repeated, and particular repeated regions allow for hydrogen bondings.1424

This bonding occurs between the electronegative oxygen atoms and the hydrogen atoms attached to the nitrogen.1434

So, remember your basic amino structure. There is an R-group.1450

There is a carboxyl group. There is hydrogen, and there is an amino group.1454

And the hydrogen on the amino group is attracted to the electronegative oxygen atoms in these carboxyl groups.1460

This would cause hydrogen bonding between one amino acid and another nearby amino acid.1468

We are not talking about the side chains. We are just talking about the backbone structure, which is this part.1475

The electronegative oxygen and a hydrogen atom attached to a nitrogen can form hydrogen bonds.1482

If there are certain repeated regions, particular types of repeated regions, you can end up with either this helix shape - it is like a spiral -1491

or what is called a beta-pleated sheet, and it is like if you took a piece of paper or something and folded it up.1503

So, this is the alpha-helix and beta-pleated sheet.1509

The important thing to remember about secondary structure is that the hydrogen bonding is between the polypeptide backbones, not the side chains.1521

And that the two main types of secondary structures are alpha-helices and beta-pleated sheets.1528

Again, one hydrogen bond is not that strong, but many hydrogen bonds together could hold the structure in place and stabilize it.1534

The next level of structure is tertiary structure, and tertiary structure is the overall 3-dimensional shape of the protein.1545

This shows a protein that might be described as a globular protein. It is shaped like a globe.1554

An example would be hemoglobin.1561

Within this overall 3-dimentional or tertiary structure, certain regions may have an alpha-helix.1568

Maybe this region over here is beta-pleated sheet, and this is beta-pleated sheet; and this is neither.1575

And then, there is another alpha-helix here and here.1582

The entire polypeptide does not usually form one big alpha-helix or beta-pleated sheet.1585

Often, there is just little regions of each in certain areas of the protein, and then, those regions, along with the rest of the protein, fold into a unique shape.1591

And the shape is extremely important to the protein's function.1603

When we talk about enzymes, you will see that the shape of the enzyme is crucial in it being able to facilitate a reaction.1606

There are five types of interactions that form and maintain the tertiary structure.1617

The first one is hydrogen bonding, but this time, it is of those side groups.1630

Remember that hydrogen bonding between a main polypeptide backbone will form secondary structures such as alpha-helices and beta-pleated sheets.1640

Those amino acids that contain hydroxyl groups or amino groups, for example, can hydrogen bond and help to stabilize the 3-dimensional structure.1648

The second type of bond is ionic bonds.1662

Remember that there are certain charged side groups.1665

We talked about the fact that there are some amino acids that are acidic and some that are basic.1670

So, those are charged, and they can form ionic bonds with each other.1675

The third type is known as a disulfide bridge.1679

Cysteine is an amino acid that contains SH on its side chain.1688

Two cysteine molecules can each lose a hydrogen and form what is called a disulfide bridge or bonds.1694

If I have two cyteins near each other, and they each lose a hydrogen; and they form this disulfide bridge or disulfide bond.1705

And this is a covalent bond, but it is still a crucial in forming the tertiary structure.1712

The fourth type is hydrophobic interactions, and what this refers to is that non-polar or amino acids with1719

non-polar side chains often end up clustered in the central part or in the middle of the protein structure.1732

And this is because those amino acids that have polar side chains can form hydrogen bonds with water.1740

So, when proteins are in a solution, the side chains that are polar interact with the water molecules.1746

They form hydrogen, and then, the non-polar ones pretty much just end up excluded from that and pushed to the center.1752

And when these non-polar ones are near each other, they can form various bonds and non-polar interactions.1758

There is one type of interaction between non-polar molecules that are called Van der Waal reactions.1765

These are another type of weak bond, and these form between non-polar molecules.1774

Again, the tertiary structure is the overall shape of the protein. It involves bending and folding.1781

And there are five types of interactions that form and maintain the tertiary structure: hydrogen bonding between the side groups,1787

ionic bonds between side groups that are charged, disulfide bridges between cysteine molecules, hydrophobic interactions, and finally, Van der Waals interactions.1796

There is one final level of structure only for certain proteins, and this is quaternary structure.1807

There are certain proteins that are formed from more than one polypeptide chain.1813

And the interaction between multiple chains in a multi-subunit protein is known as quaternary structure.1817

An excellent example is hemoglobin. Hemoglobin has four polypeptide chains that form the four sub-units of hemoglobin.1823

And not only does each of these chains have a certain tertiary structure,1833

but all four of the chains come together in an overall structure known as a quaternary structure.1837

When you think about protein folding, you need to be aware that certain conditions affect folding.1844

There is an optimal temperature for the folding of proteins. There is an optimal pH and osmolarity or salts concentration.1849

If for example temperature is changed, if a protein is heated up, it melts or unfolds, and we call this "denatures".1861

When a protein denatures, it means that it unfolds.1871

If the pH is changed, if you take a solution and add a bunch of salt to it, the proteins in it could also denature.1875

Proteins function optimally at certain conditions depending on that protein.1882

Like in our bodies, the pH, most areas of our body is about 7.4, so most of the proteins in our body function best at that pH and at our body temperature.1888

If a protein denatures, since formed for all those function, it is not going to function very well.1898

Now, let's go ahead and review some examples focusing on nucleic acids and proteins.1905

Write the complimentary strand for a strand of DNA with the following sequence.1911

Alright, this shows the 5-prime end and the 3-prime end, and then, it shows a sequence G-C-C-A-G-T-T-C-A-A-G for DNA, so, this is at different nitrogenous bases.1917

The first thing in a question like this is to remember that the two strands are anti-parallel.1932

So, right away, as part of the answer, you should always write in the 3-prime and the 5-prime, and they are going to be opposite because it is anti-parallel.1936

The strand is going to be anti-parallel and complimentary.1944

Remember that G forms three hydrogen bonds with C, and A forms two hydrogen bonds with T; so these are the ones that pair up.1948

Therefore, when there is a G, it is going to pair up with the C. A C will pair up with the G, again, with the G.1960

Here, I have an A. It pairs with T.1967

G pairs with C. 2 Ts, these each pair with A.1970

C pairs with G. As pair with T and finally, G and C, so the complimentary strand is going to be 3-prime to 5-prime.1975

The Gs will be paired with Cs. Cs will be paired with Gs.1985

A and T go together and T and A.1989

This is the complimentary strand for this strand of DNA.1993

Example 2: list two differences between DNA and RNA.2001

Well, recall that RNA contains uracil. DNA contains thiamine- that is one difference.2006

Second difference: RNA is single-stranded. DNA is double-stranded.2023

And they only ask for two, but the third difference is that the sugar for RNA is ribose, whereas the sugar for DNA is deoxyribose.2040

Here is three differences. Any two would have sufficed to answer the question: difference in nitrogenous bases,2061

single versus double-stranded and ribose sugar versus deoxyribose sugar.2067

Is each of the following amino acids polar, non-polar, acidic or basic?2076

To determine that, remember you are just going to look at the side chains, the side chains right here, here and this whole region here.2080

I am not going to pay attention to this carboxyl or amino group that is present on the backbone.2090

Right here, this is the simplest amino acid - I mentioned before - which is glycine, and glycine is non-polar. It just has a hydrogen.2098

This second amino acid is serine. Serine, you see, has a hydroxyl group, which is polar, so this is a polar amino acid.2109

Lysine is a little bit more complicated, and you will notice that it has an amino group.2120

When this is put in solution, this amino group is going to pick up a hydrogen ion and become NH3+. Therefore, it is basic.2126

We have three amino acids, three different categories: non-polar hydrogen side chain, serine is polar with a hydroxyl group,2135

and finally lysine, which is a basic amino acid.2142

List four types of interactions that maintain the tertiary structure of a protein.2148

The first one is hydrogen bonding, and remember that this is hydrogen bonding between the side groups or the R-groups, not between the backbone.2154

Second type is hydrophobic interactions.2169

These occur as a result of amino acids with hydrophobic side chains being pushed towards the center of the2175

protein being excluded from the hydrogen bonding of water and the polar side chains of some of the other amino acids.2182

These are hydrophobic interactions.2188

A type of weak interaction between non-polar side chains is called Van der Waals interactions.2191

If there are some cysteine containing amino acids that are cysteine, they contain sulfur,2203

then, there may also be disulfide bridges that help to maintain this tertiary structure.2210

This was four, but a fifth one is ionic bonds between amino acids that are charged.2218

So, here is five. Any four of these would answer the question of the four types of interactions that maintain the tertiary structure of a protein.2231

That concludes this lecture on Educator.com.2239

Thanks for visiting.2242

Welcome to Educator.com.0000

Today is the first in a series of lectures on animal physiology.0002

Throughout these lectures, we are going to talk about various groups of animals but, the focus is going to be on human anatomy and physiology.0007

And we will be starting out with the respiratory system.0015

First, an overview of gas exchange in animals, respiration is the process through which gas exchange occurs.0019

And during respiration, animals take in a respiratory media such as air or water.0026

And they extract out the oxygen and release carbon dioxide back into the air or for aquatic animals, into the water.0033

This is a necessary process for aerobic respiration, so as you will recall, animals undergo aerobic respiration in which they generate ATP.0042

After taking in the gas, the oxygen, it will diffuse down its concentration gradient into the cells of the animal.0055

And the CO2 will diffuse down its concentration to leave the animal's body.0064

Ventilation is the movement of air across a respiratory surface, so when we talk about ventilation in humans, we are talking about breathing,0070

so, breathing in and allowing the air to move across the respiratory surface of the lung.0080

When we talk about aquatic animals, then, we are talking about ventilating the gills, so movement of water across the respiratory surface of the gills.0089

Gas exchange occurs across different surfaces in different animals.0099

In some animals, it is the skin like in earthworms. In other animals, like I mentioned, the lungs, and still on others, it is gills.0105

Although the respiratory surfaces differ, there are some characteristics they have in common,0113

so general characteristics of respiratory surfaces such as lungs, gills or even skin.0119

Characteristics include the fact that the respiratory surface is generally thin to allow diffusion, to allow gas to diffuse across that surface.0134

Second, the surface is moist. Lung tissue is moist.0144

The skin of a frog, of amphibians, that use their skin as a respiratory surface is thin and moist. Finally, these structures have a large surface area.0149

In simple animals such a sponges, Hydra and flatworms, all of the body cells are in contact with the external environment.0165

So, gas exchange can take place across all the body surfaces.0174

However, as you are going to see in most animals, there are specialized surfaces for gas exchange.0177

We are going to start out by talking about gas exchange in aquatic animals.0187

Gas exchange in simple aquatic animals occurs via diffusion across the whole surface of the body.0196

That is what I just mentioned, and simple aquatic animals would include Hydra and jellies.0204

These are some of the simpler aquatic animals, and all of their cells are in contact with the water.0214

And therefore, oxygen can diffuse directly into the cells, and carbon dioxide can leave the cells and exit into the water.0221

However, in more complex aquatic animals such as fish, sharks, crustacean, gills are the means of gas exchange.0230

And the specific structure and location of gills varies among the different species. However, there are those common characteristics that I talked about.0240

Gills have a large surface area due to extensive foldings, so this increases the area available for gas exchange to occur.0251

As I also mentioned, ventilation is the movement of the respiratory media, in this case, water across the respiratory surface.0260

The gills are ventilated. Water is moved across the gills, so ventilation by movement of water across the gills, and this can occur is two essential ways.0271

One is that if we are talking about a fish, the fish moves, and water flows across the gills. The fish swims.0293

It keeps its mouth open. Water will enter the mouth, and it will flow across the gills.0307

However, even if a fish stays still, even if it stops swimming, it can still undergo ventilation. It still needs that flow of oxygen containing water.0311

So, this can occur a second way in that structures move the water across the gills.0320

In the fish, what it does is that the fish will draw water into its mouth, and then, the water will exit across the gills.0335

So, it is not just swimming, and the water is just passively entering the mouth. It is actually drawing water into the mouth.0343

And recall when we talked about the structure, the anatomy of fish, that there is a structure called an operculum- the bony structure.0348

It is a flap that protects the gills, and it also, helps keep the water moving through the gills.0360

In other aquatic animals, there are various other structures that push or move the water through.0365

An important concept in gas exchange in aquatic animals is that of countercurrent exchange.0373

Countercurrent exchange, this picture here, shows countercurrent exchange.0381

An example of it is the exchange of materials between fluids that are flowing in opposite directions, so exchange of materials or heat.0387

So, I am going to note that it can be an exchange of materials or heat between fluids moving in opposite directions.0404

In this case, we are talking about the exchange. We are going to focus on the exchange of oxygen.0420

This exchange occurs across a semipermeable membrane.0428

What happens is, there is water that enters the gills, and it is going to be flowing in this direction as shown.0432

Meanwhile, there is blood in the capillary, and this blood is returning from the tissues and cells of the body; so it is very low in oxygen.0444

It would not actually go all the way down to zero, but just for simplicity, I am going to show the water entering from the gills at 100% oxygen saturation,0455

and the water that is in the capillaries coming back from the body at 0% oxygen saturation and then, going on and increasing from there.0467

So, it is just for simplicity.0477

So, what happens is, the blood from the capillaries is depleted of oxygen, and it is flowing in this direction.0480

The water is entering the gills flowing in the opposite direction, and it is flowing across the gill, flowing across the gill; and oxygen is being extracted from it.0488

So, what you will see is that as oxygen diffuses across the membrane of the capillary from the water into the capillary,0497

what is going to happen is the oxygen saturation is going to drop.0509

So, maybe, this goes down to 90 and then, say 80, 70, 60, 50 and on and on down, but it is only going to go as low as 10- what I am showing here.0514

As the water flows across the gill, it is giving up its oxygen to the blood flowing in the opposite direction in a nearby capillary.0530

When the water enters the gill, it is going to pass very close to capillaries with blood flowing in the opposite direction, so this oxygen saturation is dropping.0540

Meanwhile, the blood in the capillary is picking up oxygen, so the saturation of the oxygen in the capillary is increasing.0552

At any point, though, in this exchange system, the percent of oxygen or the partial pressure of oxygen0564

- you can look at it that way - in the water is higher than the percent of oxygen in the blood.0575

So, even though this oxygen is increasing, and this one is decreasing, at any given point,0583

let’s say right here in the blood, there is 80 percent oxygen 70, 60, 50, 40, 30, 20, 10,0590

if I pick any point right here, even though this water has lost a lot of its oxygen, it still has more oxygen than the blood passing by at that same point.0603

So, oxygen will still diffuse down its concentration gradient.0616

The water in the gill essentially stays ahead of the blood in terms of oxygen concentration.0621

At any point in the system, the oxygen concentration in the water is greater than the oxygen concentration in the blood.0631

And what this allows is for there to be the exchange of gasses throughout the entire length of the system, the entire length of the capillary.0656

In this way, the blood is able to continually, as it moves through, pick up oxygen, and the water is able to give up its oxygen.0666

And if you look here, what this blood is encountering is water that has depleted of a lot of its oxygen.0678

However, this blood has even lower oxygen because it is just returning from the body.0689

So, it is set up so that the oxygen concentration of the blood at any point is lower than the oxygen concentration of the water.0694

And that is the essential point.0702

Now, as I said, heat can also be exchanged through a countercurrent system, and this is a mechanism for temperature regulation.0705

So, countercurrent exchange is used in thermoregulation. These systems are used in thermoregulation in some animals.0714

As an example, marine animals that have their legs or flippers submerged in cold water can use this system.0728

If an animal, say, has its legs submerged in cold water, the blood in the extremities is going to be very cold.0738

And what happens is, the vessels carrying the cold blood, the veins carrying the cold blood... so, let's show this here.0746

This is a vein, and this is going to be blood from the extremity; and this is cold because it has been submerged.0760

The animal's paw has been submerged in water. It gets very cold, and the blood returning to the heart is cold.0772

Meanwhile, arterial blood is going to be in nearby arteries that are running in the opposite direction.0779

The blood is flowing in the opposite direction, and this is blood coming from the heart. It is coming from their body core that is warmer.0789

And what will happen is heat will be transferred at every point along this countercurrent exchange system.0797

And that, then, warms the blood that is returning to the core of the body and cools the blood going out to the extremities.0806

And the result is that there is not as much heat loss from the extremities, so it maintains the body temperature- thermoregulation.0816

Alright, so, this is gas exchange in aquatic animals.0827

Now, we are going to talk about gas exchange in terrestrial animals, in land animals0831

starting out with simpler animals that rely on the diffusion of gasses across the skin.0839

Now, we talked about very simple animals where all cells are in contact with the external environment like in a flatworm.0849

The gas can just diffuse in, and oxygen can diffuse in. CO2 can diffuse out.0858

If you look at a little bit more complex animal, an earthworm - so, let's talk about earthworms, which are annelids, segmented worms -0863

gas exchange occurs across the skin.0873

So, the skin is not just a surface for protection in these animals, it is also a respiratory organ, and this is an external respiratory surface.0881

In us, we have lungs. They are located inside our bodies.0896

Those are internal respiratory surfaces. This is an external respiratory surface.0899

And what happens is the oxygen enters the skin, and then, it encounters a rich network of capillaries.0904

And the oxygen enters those capillaries. Carbon dioxide leaves the capillaries and diffuses across the skin.0911

However, in many animals, the skin alone is not sufficient for gas exchange.0917

So, when we talked about amphibians like frogs, gas exchange across the skin is just a supplement for gas exchange via the lungs.0922

And then, in many larger, more complex animals, the skin is not a respiratory organ. In fact, there are just internal respiratory surfaces.0930

So, let's talk about internal respiratory surfaces like lungs.0939

One major advantage to an internal respiratory surface is that they minimize water loss, so an internal respiratory surface minimizes water loss.0945

Recall that respiratory surfaces need to be moist, and therefore, if the skin is a respiratory surface like in a frog, it needs to be moist.0957

And the animal is restricted to a moist environment, so an earthworm in a dry environment will dry out.0967

Gas exchange will not occur. It will die, so internal respiratory surface allows animals to live in drier environments.0973

The internal respiratory surfaces are moist, and they are lined with epithelium.0984

But as I said, this moist epithelial surface is confined to the inside of the animal's body.0993

Before we go on to talk about mammalian and specifically human respiratory systems, we are going to talk about arthropod respiratory system.0999

So, we are going to focus actually on insects and just use that as an example of a different type of respiratory system, although, it is an internal system.1008

If we look at gas exchange in insects, what happens is air enters the body through openings in the body called sphericals,1016

so, openings that are called sphericals, the gas enters.1029

So, air enters the sphericals then, goes into tracheae. Singular would be trachea.1037

The tracheae branch, and they become smaller and smaller; and these smaller structures are called tracheoles.1055

Air enters the sphericals then, goes to the tracheae and a trachea will branch into a tracheole.1064

And these will get smaller and smaller and smaller and branch more and more until they reach the various cells in the body.1072

And they will deliver the air directly to the cells.1081

So, gas exchange occurs at the epithelial surfaces that are at the end, so branching, branching, branching.1086

And then, here at the end of the tracheole, we have a spherical where the air enters.1093

And then, it is the trachea and then, tracheoles, and then, at the end of the tracheoles is an epithelial surface.1105

And the body cells, there will be an organ or a structure right here, and then, gas exchange occurs.1115

Notice that the gas, the oxygen is not going into blood like it does in us.1125

It is not going from a lung to blood and then, being delivered to cells. It is going directly from the respiratory surface to the cells.1130

And oxygen diffuses out to the cells. CO2 is picked up.1140

Something important here, a fundamental difference between this system and, say, our system is that the circulatory fluid.1149

In arthropods, the circulatory fluid, and we will talk about this in detail on the lecture in circulation about the circulatory fluids.1155

The circulatory fluid in arthropods is called hemolymph, and although, hemolymph sometimes delivers oxygen in certain arthropods,1164

in most arthropods, the job of hemolymph, of the circulatory fluid, is to deliver nutrients, hormones, pick up waste products.1173

But, it is not a source of gas exchange or gas transport. Oxygen and CO2 does not usually transport oxygen- like I said, not usually.1183

In some animals, it does, and we will talk about that later.1199

But for now, what you should know is that in insects, the respiratory surface directly delivers the oxygen and picks up the CO2 from cells.1202

It does not use the intermediary circulatory system to deliver oxygen and pick up CO2.1213

Now, in larger insects they need even more air to supply their tissues, and they sometimes will then have air sacs at the end of the tracheae.1219

And what happen is, as the insect moves, the air sac will expand.1232

And this allows the sac at the end - sort of like an alveolus - allows for a greater amount of oxygen to be delivered.1237

So, this is an example of a system in a non-mammal.1250

One thing, though, that is a commonality between various respiratory surfaces, as I said, is their large surface area.1259

And we talked about the folding of gills. Folding is one way to increase the surface area.1267

Here, there is branching, so these are highly branched structures.1272

Branched tubes and folded structures, those are commonalities in respiratory surfaces.1276

Now, we are going to talk about the human respiratory system.1282

And many of the structures that we are going to discuss such as lungs are found in mammals1286

other than humans and even non-mammalian vertebrates like reptiles and amphibians.1292

Even some of the invertebrates have lungs, but I am really going to be focusing on the human respiratory system.1299

And that is what is really important especially to know for the Advanced Placement Exam.1304

We are starting out at the top air containing oxygen is going to enter via the nasal cavity.1310

So, it enters via the nasal cavity, and a few things occur in the nasal cavity.1319

The air is warmed. The air is also humidified.1326

It gains moisture, so it is moistened or humidified, and finally, it is filtered. There are hairs in the nasal cavities that catch particulates such as dusts.1332

So, the air is warmed, humidified and filtered.1344

So, that air enters the nasal cavity, and the next structure that you need to be familiar with is the pharynx.1348

After passing through the pharynx, a little bit lower down is the larynx.1360

Within the larynx is the voice box, so in addition to being a respiratory structure, the larynx is important for speech.1368

And vibration of the vocal cords within the larynx is what produces speech.1377

There is a structure called the epiglottis.1384

And when we swallow food or fluids, then, the epiglottis covers the larynx so that food or fluid does not enter the lung.1389

Instead, the food or fluid goes into the esophagus, and we are going to look at the structure of the epiglottis more when we talk about the GI system.1398

But for now, just know that the epiglottis protects the airway and that it covers1406

the opening to the larynx so that food and fluid cannot end up in the lung.1411

So, the air has gone through the pharynx and larynx and then, enters the trachea, continues on down into the right and left bronchi.1419

So, here, we are just looking at one side.1433

If he is facing you, then, this is his left bronchus, so focusing on this one side, but the same structures are also found over here on the other side.1435

Air continues into the bronchus.1451

Then, the bronchus branches into these smaller structures called bronchioles,1456

which terminate in very small sac-like structures called alveoli or singular, alveolus.1464

So, this is the pathway of air through the respiratory system:1474

nasal cavity or mouth, pharynx, larynx, trachea, bronchus, bronchiole and alveolus, which is the site of gas exchange.1478

A couple things you should know is that the trachea contains cartilaginous rings, so rings of cartilage.1490

This maintains the strength, the structure and the support to hold this into a tube shape, so these cartilaginous rings.1501

The other thing you should be aware of is that the respiratory tract is lined with cilia, so the respiratory tract is lined with cilia and contains mucus.1511

So, what happens is certainly, the nose, the nasal cavity has filtered out some of the particulates but not 100%.1526

So, other particulates can be trapped in this mucosal layer, and then, the cilia move.1533

And what they do is they push the mucus upwards to remove any more particulates from the respiratory system.1540

So, the air has now made its way down to the alveolus, and this is the surface across, which gas exchange occurs.1551

The alveoli are microscopic structures, and taken together, they have a huge surface area.1561

They have a surface area of about - if you put them all together - 100 square meters.1567

Let's say this is an alveolus, and then, there will be a nearby capillary.1577

And oxygen will go down its concentration gradient from high concentration of oxygen in the alveolus to the lower concentration of oxygen in the capillary.1588

Meanwhile, CO2 is going the other way, so gas exchange occurs across the membrane of the alveolus.1600

The alveolus is surrounded by fluid, and then, it will cross the capillary membrane and enter the blood.1611

Again, this is in contrast to the tracheole system that we talked about in insects.1617

In insects, the tracheae branched and branched into tracheoles that, then, deliver their oxygen right to the body cells.1622

So, it could be the leg of the insect. It could be the sensory organs of the insect, the nervous system.1632

It is all getting delivered directly there, whereas here, there is not a respiratory surface next to all parts of the animal's body.1643

There is not an alveolus over in the hand or going all the way down into the leg to directly deliver gas.1651

Instead, the respiratory surface gives the oxygen to the circulatory system to the blood.1658

And the circulatory system, then, delivers that gas to the tissues and organs in the body.1664

So, the alveoli are surrounded by tiny capillaries.1671

Oxygen diffuses out of the alveolus into nearby capillaries, and CO2 diffuses in the opposite direction and then, can be exhaled out.1676

Pulmonary surfactants are substances found in the lung that lower the surface tension in the alveolus, in the alveoli.1686

What this does is it prevents alveolar collapse, so it prevents the collapse of the alveoli.1706

Premature infants sometimes suffer from a syndrome called RDS. This is respiratory distress syndrome.1719

And the reason is that surfactant does not developed until late in gestation until late in pregnancy.1729

So, if a baby is born prematurely, and there is not enough surfactant being produced, then, they are at risk for respiratory distress syndrome1736

because their lungs are not ready to be taken over that function of breathing, and the result is respiratory distress.1744

OK, before we go on and talk about ventilation, just a brief discussion of the circulatory system since it is very closely related to the respiratory system.1755

Although, there is going to be another lecture on that topic.1764

Once the oxygen is picked up by the capillaries, it enters red blood cells, and the red blood cells contain hemoglobin.1767

The hemoglobin contains iron, and the iron is capable of binding the oxygen.1780

So, the red blood cells use hemoglobin, and the iron within the hemoglobin, to carry oxygen to the cells.1787

And we will talk all about the structure and function of hemoglobin in the next lecture.1796

Carbon dioxide: some of it is transferred by hemoglobin.1800

But, most carbon dioxide is transferred in the blood plasma via a buffering system, so most CO2.1805

So, hemoglobin transport oxygen, whereas, most CO2 is actually transported in the form of bicarbonate ion in the plasma.1813

Alright, we have talked about the flow of air through the respiratory system and how gas exchange occurs.1824

Now, we are going to talk about ventilation in the human respiratory system.1829

Recall that ventilation is the process of moving air - in this case air - across the respiratory surface, which is the lung.1834

Ventilation occurs during the process of breathing.1843

So, breathing consists of inspiration, taking the air in, and expiration in which the air is moved out of the body.1846

And ventilation or breathing occurs differently in various species.1857

For example birds lack diaphragms, and we are going to talk about the diaphragm muscle.1863

Birds do not have diaphragms, yet, they still breath very effectively.1868

We are going to focus on mammalian ventilation, and in mammals, there is a sheet of muscle called a diaphragm.1872

This is a sheet of skeletal muscle that is located in the thorax.1881

So, you have the lungs, and then, just below that, it is a dome-shaped muscle. That is the diaphragm, and the diaphragm separates the body cavities.1887

Up here, above the diaphragm is the thorax, and then, below is the abdominal cavity.1902

Contraction of the diaphragm moves it downward, so it flattens out somewhat and the result... so, it moves downward1912

So, as you can imagine then, you have the lungs here, but then, the diaphragm drops down along with the...1921

The lungs expands as well. Did we draw that?1932

So, we have expansion, then, of the thoracic cavity, so the thoracic cavity becomes larger.1936

Right here, it states that air is pulled into the lungs by negative pressure.1947

And this negative pressure, meaning that the pressure in the thoracic cavity becomes lower than1951

the pressure outside in the atmosphere, is a result of the increase in size of the thoracic cavity.1958

So, increased size of the thoracic cavity is the result of the diaphragm contracting.1966

The diaphragm contracts and moves downward, and the rib muscles contract.1975

And when the rib muscles contract, the ribcage moves outward, so the ribcage expands. It moves outward.1995

The downward movement of the diaphragm combined with the outward movement in the ribcage results in a cavity that is larger than it originally was.2006

So, the thoracic cavity becomes larger. The result is negative pressure, and air is pulled into the body; and it is pulled into the lungs, as well.2016

As the thorax expands, the lungs expand and air rushes in.2024

In exhalation, the reverse process occurs, so this is during inhalation or inspiration of air. During expiration, the opposite occurs.2029

During expiration, the diaphragm relaxes. Rib muscles relax.2043

And we end up with a thoracic cavity that is decreased in size - decreased size thoracic cavity - and therefore, the air rushes out of the body.2057

Not every single last bit of air leaves the lungs during exhalation. There is a little bit of residual air left.2067

Alright, so, we talked about the process of breathing. Now, what controls the breathing? The breathing control center.2075

The breathing control center is located in the brain stem in a couple of structures called the medulla oblongata or just the medulla and the pons.2086

So, the medulla and pons are the breathing control center, and what the medulla does is it monitors the CO2 level in the CSF.2098

CSF stands for cerebrospinal fluid. Cerebrospinal fluid is the fluid surrounding the brain.2111

Actually correction, it monitors pH. It monitors pH, which is closely related to the CO2 level, OK?2120

So, it monitors the pH in the CSF, and the pH in CSF is reflective of the pH in the blood.2134

What happens in the blood is the blood goes to the cells and the tissues of the body, and then, it picks up CO2.2142

And in the red blood cell, the CO2 combines with water to form carbonic acid,2152

which dissociates into bicarbonate and hydrogen, so bicarbonate ion and hydrogen ions.2162

Therefore, if there is a lot of CO2 in the blood, the blood will be a little bit more acidic because a lot of CO2 is going to push this reaction.2172

It is a reversible reaction, but it is going to be pushed to the right if you are putting CO2 into the system.2185

And the result is going to be an increase in hydrogen ion, and when hydrogen ions go up, pH goes down.2189

So, the pH of the blood is usually...a typical pH is 7.4, but when you are exercising a lot, then, the pH of the blood could drop a little bit.2196

During periods of activity, you are running, you are exercising, you need more oxygen.2208

And therefore, you need to breathe faster, and the way your body knows that you need more oxygen is you are generating CO2.2214

By generating CO2, you are going to be generating hydrogen ions, and the pH in your blood will drop.2223

When the pH in the blood drops, so decreased pH in the blood will be reflected in the CSF.2230

So, decreased pH in the blood triggers an increase in the rate and depth of breathing- increased breathing, rate and depth.2238

So, this is triggered. You are going to breath more quickly and more deeply.2252

And then, once pH rises back up to its normal level, then, the medulla will slow the rate back down.2257

Therefore, breathing, respiratory rate is primarily determined by carbon dioxide and not by oxygen.2264

The body, via looking at the pH, is actually monitoring the CO2 level.2272

Now, oxygen does play a role.2277

The term for low oxygen is hypoxia, and there is a second set of mechanisms that can detect low oxygen.2280

They are actually oxygen sensor, for example, located in the arteries in your neck, in the carotid arteries.2291

So, if oxygen became concerningly low, that system would kick in and tell you to breathe.2297

But primarily, breathing is a function of the CO2 level and not oxygen levels.2306

I mentioned the medulla, and the medulla sets the rate of breathing.2313

However, the pons modulates or modifies the breathing rhythm. It just makes sure that it is nice and even and smooth.2318

So, the breathing rate is set by the medulla, but it is adjusted or modulated. The rhythm of breathing is modulated by the pons.2326

OK, today we talked about the respiratory systems in different animals especially in humans.2336

We talked about gas exchange, ventilation and structures involved in respiration.2342

And now, we are going to do some practice questions starting out with example one.2347

Describe the tracheal system in insects. Include the terms spherical, trachea and tracheole in your discussion.2352

Well, in insects, air enters via openings in the body called sphericals.2360

It, then, enters tracheae, and these tracheae branch and become smaller and smaller and form tracheoles.2371

The tracheoles reach the cells of the body, and gas exchange occurs.2382

So, the respiratory system brings air directly to body tissues and cells.2390

Oxygen is picked up by the cells, so oxygen is picked up, O2 delivered to the cells; and CO2 is picked up.2399

The circulatory fluid, the hemolymph generally does not deliver the oxygen or pick up the CO2.2415

It is delivered directly by the respiratory system.2423

Also, in some insects, there are air sacs. There may be air sacs at the end of the tracheoles to increase the amount of air that can be delivered.2426

Also, note that the larger branches of this system contain chitin for support, so there is some chitin in the tracheae.2439

How does the tracheal system differ from the respiratory system found in mammals? Well, obviously there are different structures that we talked about.2454

The respiratory system in mammals, we talked about structures such as the pharynx, the larynx, the bronchi, the alveolus.2464

But, a major difference - just a concept that you should understand - is that in the tracheal system, tracheal system delivers air directly to body cell.2474

So, oxygen is delivered directly by the respiratory system.2492

CO2 is picked up directly by the respiratory system, whereas, in mammals oxygen is delivered by the blood, by the circulatory system.2497

And CO2 is picked up by the blood.2510

The circulatory system does not act as a delivery route in insects for gas exchange.2517

Whereas, in mammals the circulatory system plays this intermediary role.2524

What role does the countercurrent exchange system play in gas exchange in fish?2531

Well, first, recall what a countercurrent exchange system is. It is fluids that are flowing near each other, but they are going in opposite directions.2536

So here, we have water enters the gills and flows in this direction.2547

Meanwhile, we have blood in a capillary nearby, and it is flowing in the opposite direction; and this is blood from the body that is deoxygenated.2556

So, this blood is going to have a very low O2 saturation. We will just call it zero, and this is going to increase, let say 20, 40, 60, 80.2572

Meanwhile, the water entering the gills is going to start out with oxygen, let’s say, up at 100, and that is going to drop.2589

As the water passes near this blood, the oxygen is going to diffuse down its concentration gradient and enter the blood.2605

Meanwhile, CO2 would diffuse the other way.2619

So, as the water passes through the gills, the O2 concentration will drop.2622

However, at any given point, the O2 concentration in the water is greater than the O2 concentration in the blood.2628

So, all on this exchange system, gas exchange is occurring.2637

So, that is the role of a countercurrent exchange system in gas exchange in fish.2645

Example three: place the following structures in the order in which air travels after entering the respiratory system via the nasal cavities.2653

So, after entering the nasal cavities where the air is warmed, it is moistened and it is filtered.2662

The next step is going to be the pharynx, so the pharynx is going to be the next structure that the air will pass through.2670

From the pharynx, air will enter the larynx, so we did pharynx. We did larynx.2679

From there air, travels to the trachea, and that is going to branch off into the right and left bronchi; so it is going to enter a bronchus.2687

The bronchi, bronchus, if we are talking about one, is going to branch into smaller bronchioles.2703

And those are going to terminate in an alveolus, which is the site of gas exchange between the respiratory system in the blood.2711

So, this is the order that air travels through the respiratory system.2721

Example four: what role does the diaphragm play in ventilation?2733

Recall that the diaphragm is a sheet of muscle located in the thorax separating the thoracic cavity and the abdominal cavity.2737

When the diaphragm contracts, it moves downward. Therefore, the size of the thoracic cavity will be increased, so increased thorax size.2747

The result is going to be negative pressure in the thorax, and that pulls air in during inspiration. The opposite will occur when the diaphragm relaxes.2765

It is going to move up, and there is going to be a decrease in the size of the thorax. Air, then, will rush out of the lungs during expiration.2791

What role does pH have in the regulation of breathing by the medulla?2809

Well, the medulla monitors pH in the CSF, and the pH in the CSF mirrors the pH in the blood; so this is a measure of pH in the blood.2813

And in the blood, when CO2 increases, the result is that pH decreases because recall CO2 plus water form carbonic acid,2837

which associates to bicarbonate ion and hydrogen ion, so increased CO2 translates the increase hydrogen ion, which is decreased pH.2858

Decreased pH leads the medulla to increase the rate and depth of breathing.2869

So, when the medulla senses that pH has dropped, there is an increase in the rate and depth of breathing.2881

That concludes this lecture on the respiratory system.2888

Thanks for visiting Educator.com.2892

Welcome to Educator.com.0001

We will be continuing our discussion of animal physiology with the circulatory system.0002

The purpose of the circulatory system is to deliver oxygen, hormones and nutrients to the cells of the body0010

and to remove wastes including CO2 as well as other waste products from metabolic processes.0017

In simple animals such as sponges and jellies, all the cells are in contact with the external environment,0024

which means that a circulatory system is not necessary.0031

These cells can pick up nutrients and oxygen directly from the water, and these components can enter the cells via diffusion.0035

And then, waste products can exit into the water the same way.0045

Animals such as sponges and jellies have bodies that are only a couple of cell layers thick, so they are in contact with the water on the outside.0050

And then, on the inside of the body, you may recall, they have a gastrovascular cavity.0059

As the name suggests, it combines both vascular system functions and GI tract functions and allows that inner layer of cells to be in contact with the water.0068

So, there is no heart, vessels, no circulatory fluid, no blood.0079

A similar idea occurs in flatworms. Flatworms, due to their very flat body structure, also have cells that are entirely in contact with the environment.0085

So, their bodies are in very close contact with the environment, and by diffusion, oxygen can enter.0097

However, most animals are larger and more complex than these, and they cannot exchange gas and nutrients directly with the environment0105

for every single cell in the body, because most of their cells are not even in direct contact with the environment.0114

In the section of respiration, we talked about gas exchange and the idea that specialized respiratory systems include structures like lungs and gills,0122

which provide a means of gas exchange.0132

However, the oxygen needs to be delivered to all the cells of the body, and some of these cells are distant from where gas exchange is taking place.0135

Gas exchange takes place in the alveolus of the lung. However, the alveolus is nowhere near your leg.0144

So, somehow, that oxygen needs to get to the leg or the arm or the brain throughout all the cells of the body.0153

Diffusion is one way that gases can move, but this would be far too slow.0160

Waiting for oxygen to diffuse down to your leg or brain would be so slow that the muscle or the brain cell would die waiting.0165

So, diffusion is much too slow. In order to bring large amounts of oxygen and nutrients to the cells quickly, the circulatory system evolved.0173

I have been focusing on oxygen, but recall that nutrients that are obtained by digestion in the GI system also need to be delivered to distant cells.0184

So, animals also require a circulatory system to carry out that function, and there are two general types of circulatory systems: open and closed.0194

Here is shown an insect as an example of an organism that has an open circulatory system.0206

And an open circulatory system means that the blood at one point leaves the vessels.0213

It does not mean that there are not any vessels. There often are some vessels, but the fluid is not contained within the vessels the entire time.0219

Here, this represents a pump, so a simple heart, and the pump, the heart, will move the circulatory fluid through vessels like an aorta.0229

From there, the circulatory vessels will branch out, and then, the fluid will be dumped out, released out, into cavities called sinuses.0246

So, these sinuses surround organs, so there will be an organ in here.0258

The respiratory, or excuse me, the circulatory fluid enters that cavity, and it bathes the organs and cells in this fluid.0264

Therefore, the organ can pick up nutrients and other substances from the fluid, and it can let waste products release them out into the fluid.0273

The fluid is, then, picked back up and returned to the heart.0287

In an open circulatory system, the fluid is called hemolymph. It is not blood, and hemolymph differs from blood in some fundamental ways.0292

In organisms with a closed - so, this is an open circulatory system - circulatory system, there are two types of fluid:0303

one in the vessels and one that bathes tissues and organs called interstitial fluid.0312

Here, there is only one type of fluid. They are one and the same.0318

It is called hemolymph.0321

The other thing is that frequently, hemolymph is not the means of delivering oxygen and picking up carbon dioxide.0322

Recall from the respiratory system, animals like insects have a tracheal system that they use to deliver oxygen directly to the cells of the body.0329

They do not take in the gas, give it to the circulatory fluid and have the circulatory fluid deliver the gas.0340

Usually, hemolymph is responsible for delivering nutrients and other substances, but it is often not the means of oxygen delivery or CO2 transport.0348

This second type of system is the closed circulatory system, and here is an example of...here is an earthworm and annelid,0360

and that it will have a closed circulatory system, so most invertebrates have an open circulatory system.0371

There are exceptions such as annelids. Another exception is cephalopods have a closed circulatory system like squids and octopuses.0382

So, most invertebrates have an open system. There are some that have a closed system, and all vertebrates have a closed circulatory system.0398

In a closed circulatory system, blood remains within vessels the entire time.0409

The blood stays within the vessel. Here is the heart, blood vessel, artery, carrying blood away from the heart.0417

And these vessels, they branch out into capillaries, and oxygen and nutrients can diffuse across the walls of the capillary.0427

But, the blood does not leave the vessel. It stays in the vessel, and then, it is returned to the heart.0437

Therefore, in a closed circulatory system, the fluid within the vessels is the blood, and then, there is second type of fluid called interstitial fluid.0444

That is fluid that surrounds tissues in organs.0456

We are going to talk in depth now about mammalian circulation, again, with a focus on the human circulatory system.0463

I am going to start out talking about the different components of a circulatory system.0472

And the major components are vessels, some type of circulatory fluid - hemolymph in the open system, blood in the closed system - and a pump- the heart.0477

Starting out with blood vessels, there are three types of blood vessels that you need to know, and these are arteries, veins and capillaries.0493

Starting out with arteries, arteries pump blood or move blood away from the heart.0504

So, blood is pumped by the heart through the arteries, so they carry blood away from the heart, and they have thick muscular walls.0515

There are smooth muscles in the walls, and the walls are thick- thick-walled.0529

The blood within the arteries is under pressure. It is being pumped by the heart, so it is under a significant amount of pressure.0537

What happens is as the blood is pumped by the heart, it is under pressure when the heart contracts.0545

However, when the ventricles relax, the pressure decreases, but the thick walls of the artery prevent the pressure from the circulatory0553

system from dropping too low because once the pressure is decreased as the heart relaxes, the walls of the artery will spring back.0563

So, they are being pushed by the pressure that the blood is under, and then, they spring back.0573

And that recoil maintains the pressure within the arterial system.0579

Arteries branch into arterials and then, finally, capillaries.0585

The second type of vessel is the veins. Veins are carry blood towards the heart, so blood returning either from body tissues or from the lungs.0596

Most veins, therefore, carry deoxygenated blood. There is an exception, though.0623

By that same measure, most arteries carry oxygenated blood.0637

And I say most because there is an exception that we are going to talk about when we talk about the heart.0646

But, when you say "define an artery", it is part of the definition that it is carrying blood away from the heart.0652

Usually, it is oxygenated but not always because the blood carried by the pulmonary artery is going away from the heart.0659

It is going towards the lungs. Yet, it is deoxygenated.0670

That is why it is going to the lungs.0672

So, anyways, veins carry blood towards the heart, and it is usually, but not always, deoxygenated blood.0674

The walls of the veins are much thinner, relatively thin, compared to the arteries, and the blood in the veins is under a lower pressure than in the arteries.0681

Now, blood is returned to the heart in part by muscle contraction.0695

So, for example, the veins in your legs, when you walk or when you run, you move around.0700

The contraction of your leg muscles pushes your venous blood back up towards the heart.0704

And that is why if someone wants to improve their circulation, they need to walk around or why if somebody is bedridden,0711

they are immobile, they are at a higher risk for blood clots because the blood pools, which makes it tend to coagulate and cause a clot.0719

So, anyways, movement is important for circulation.0726

Because the venous blood is not under a lot pressure, veins contain valves.0730

And what the valves do is they prevent backflow, so it prevents the blood from draining back into your feet towards the0736

dependent lower parts of your body and helps keep blood flowing upward or towards the heart, flowing in the right direction.0745

It prevents backflow.0754

Finally, capillaries: capillaries are very small vessels, so they are very small.0757

And they have cell walls that are only a single cell thick, which allows for diffusion of nutrients and gases across the cell wall.0764

The diameter of capillaries is so small that red blood cells actually have to go through single file, so these are extremely vessels.0777

Some terms that you should understand relating to blood vessels are vasoconstriction and vasodilation.0793

Vasoconstriction refers to the constriction or narrowing of the blood vessels.0800

And this is the result of the contraction of the muscles in the walls of the artery.0813

This will result in an increase in blood pressure, so vasoconstriction increases blood pressure. The opposite is vasodilation.0819

In vasodilation, blood vessels open up. They become wider, so instead of constricting, they dilate, so dilation of vessels.0836

And this is going to decrease blood pressure.0853

For example, if somebody is bleeding, they lose a lot of their blood, their blood pressure will drop.0860

And one way to compensate for that is for the vessels to constrict, so vasoconstriction can maintain the blood pressure.0866

Vasoconstriction and vasodilation also play a role in thermoregulation.0873

Thermoregulation is the maintenance of a constant internal temperature.0879

Cold triggers vasoconstriction, so if the blood vessels constrict, their diameter becomes smaller, then, less blood will flow through these vessels.0886

So, what happens is, it is specifically the vasoconstriction of superficial vessels, near the surface of the body.0902

When the blood vessels constrict, there is a decrease of heat loss from these vessels.0913

In contrast, heat triggers vasodilation, so on a hot day, your blood vessels will dilate.0921

That is going to increase the blood flow and allowing for increased heat transfer.0934

So, heat will be lost to the environment through those dilated vessels near the surface of your skin.0943

Vasoconstriction, vasodilation, also play a role in thermoregulation.0948

So, we have talked about vessels. The second component of the circulatory system is the circulatory fluid.0955

In mammals, blood is the circulatory fluid, and it contains a fluid component and a cellular component.0962

The average adult has about 5 liters of blood.0976

So, beginning with the fluid component of blood, that is plasma, and it contains many substances:0991

gases, proteins, hormones, antibodies, waste products being carried away from cells, various components of the plasma.0999

This is the fluid component of blood.1013

The pH of blood is around 7.4, and it is in part maintained by buffers - the buffer system that we will talk about - in the plasma.1016

In addition, so I mentioned proteins, some of the proteins are in the plasma, we are talking about the pH at 7.4.1033

There is a buffer system.1040

There are also clotting factors in the plasma that allow a blood clot to form when someone becomes injured, when they are bleeding.1041

So, that is just an overview of the plasma. We will talk more in a minute about clotting factors and the clotting system.1054

The second component is the cellular component. So, there is the fluid component, which is plasma and cellular components.1063

The major cellular component is red blood cells, so the cellular component: red blood cells and white blood cells.1072

First, red blood cells: the other name for these is erythrocytes.1079

The shape is that these are biconcave discs, so they are, sort of, collapsed in - biconcave discs - and they lack a nucleus.1093

This makes more room for them to do their job. Their job is to transport oxygen, and they contain hemoglobin.1109

The more hemoglobin, the more oxygen they can transport, so by not having a nucleus, there is more room for hemoglobin.1120

Hemoglobin is a protein that contains heme groups, and within the heme groups is iron.1125

And it is the iron that allows hemoglobin to bind oxygen and then, to release the oxygen, to reversibly bind oxygen.1136

We will talk about the structure of hemoglobin and transfer of oxygen in detail.1144

Red blood cells only use anaerobic respiration, so they only undergo anaerobic respiration.1150

And it totally makes sense if you think about it because their job is to transport oxygen.1159

If they were undergoing aerobic respiration, they would actually end up using up the oxygen that they are trying to transport,1164

So, that they are not using up the oxygen, instead, they undergo anaerobic respiration only.1171

Red blood cells have a life span of about 120 days. They live 120 days, and they are produced in the bone marrow.1177

So, the job of the red blood cells is to pick up oxygen in the lungs as the oxygen diffuses from the gas-filled alveoli into the capillaries.1194

They pick up the oxygen. They transport the oxygen into the body tissues.1204

Then, they release the oxygen, and the oxygen diffuses in the body tissues.1208

They also have a role in the transport of CO2, and we will talk about that later, as well.1213

White blood cells are the second cellular component.1220

So, we have the fluid component and the cellular components, which includes red blood cells and white blood cells.1223

White blood cells or WBCs are also called leukocytes.1230

Leukocytes are produced in the bone marrow, and we will investigate these in detail when we talk about the immune system.1235

So, they are produced in the bone marrow, and they have a role in immunity. Their job is to fight infection.1245

If a person has a low white count, they are immunocompromised. They are at risk for serious infections.1251

If a person has high white count, if you test their blood and you say "wow, they have a higher than normal number of white blood cells",1257

that can indicate that they have an infection and that their body is fighting that infection.1264

We raise the number of white blood cells to fight pathogens/invaders.1270

Finally, there is a component that is not cells but actually cell fragments, and these are platelets.1275

Platelets are actually fragments of cells. They are produced in the bone marrow also, and they have a very important function in blood clotting.1282

I am going to talk briefly now also, as we are discussing blood, about blood types.1297

You have probably heard of blood types, or you may even know your blood type: A, B, AB and O and blood types positive and negative.1304

What this is referring to is antigens on the surface of blood cells.1314

If I look at a cell, I look at a red blood cell, and then, I test it; and I say, "OK, it has a particular antigen on the surface",1319

let's call the A antigen for the A blood group, and it is shaped like this, so this person is type A blood.1332

There is another antigen, the B antigen, and the B antigen, let's say, is shaped like this. That person is type B.1342

Type AB is an individual whose cells produce both the A and the B antigens.1356

Finally, type O: O is the absence of the A and B. They have neither, so they are type O.1367

The second system referring to positive and negative is the Rh. It has to do with the Rh factor.1374

So, there is another protein called the Rh factor, and the Rh factor we will say is shaped like this.1380

And if a person has the Rh factor, they are positive, so this individual is A+. If they don't have the RH factor, they are B-.1390

If they have the RH factor, they are AB+. If they do not have the Rh factor, they are O-.1400

Each type can be positive or negative depending on if they have the Rh factor.1406

Now, this is very important when it comes to transfusions because a person's1412

immune system will recognize antigens that are not present in their own blood.1417

So, if somebody is type A and you put B blood or AB blood in their body, they are going to recognize this and attack it.1425

This A+ person, if I transfuse them with B-, they will lyse. They will destroy those cells.1436

If I transfuse them with AB+, they will destroy the cells because they see the B is a foreign protein/antigen.1443

And actually, they are positive, so they will recognize this. They will recognize the A, but they will attack this B.1456

Therefore, for this person, I could give them blood that is A+.1463

I could give them blood that is A- because they just will not have the RH factor. They will not attack because of that.1470

I could also give them O, either positive or a negative.1476

Let's look at this person type B. If I give them something they do not recognize as part of their own antigen system, they will attack it.1484

So, if I give them this A+, they are going to attack it because of the A, and they are going to attack it because of this Rh factor.1493

So, I cannot give them that.1502

If I give them AB, they are going to attack the A part, and if it is positive, they will also attack this. I could give them B-.1504

Could I give them B+? Well, B+, they would have B, and they would also have this Rh factor.1516

Their body would be OK with the B. They would recognize it, but their body will not recognize the Rh factor, so they will attack.1523

One thing is that if you look at O-, it does not have A on it. It does not have B on it, and it does not have the Rh factor.1535

So, it is blank as far as these major antigens. Therefore, O- is the universal donor.1544

I could give it to A, B, AB, positive, negative. There is nothing on here to attack for the major antigens, so therefore, it is the universal donor.1555

Looking at the other way around, no matter what I give AB+, they are going to be OK with it.1566

If I give them A, great, he recognizes the A here. He recognizes the positive.1573

He will not attack it because he has got it.1577

If I give him B- or B+, they will be fine with that. He recognizes it.1580

He has all three antigens, so these all are familiar to the body. They will not attack it.1584

Therefore, AB+ is the universal acceptor.1590

So, what you have on your blood, you recognize as yourself, and you will not attack. What you do not have, you will attack.1596

So, you cannot accept blood from somebody who has got antigens that are not on your own blood.1603

You can accept O-. These are not there, but you cannot accept something that is not on your own blood.1609

So, that is blood groups, and I will explain a little bit about how blood transfusions are done.1617

OK, I mentioned that there are clotting factors in the blood. Blood vessels are lined with epithelial cells.1626

And this lining of epithelial cells is called the endothelium, so the wall of the blood vessel is the endothelium.1634

If a blood vessel is injured, the blood vessel wall, if the endothelium is damaged, platelets are activated.1651

So, damage to the endothelium triggers or activates platelets.1659

When the platelets are activated, they aggregate, and this aggregation forms an initial plug or an initial clot, and this clot starts to staunch the bleeding.1677

This is a plug to decrease the bleeding, and this is just the initial clot.1700

The clot needs to be reinforced, though, by fibrin, and so, it is later reinforced by fibrin.1711

And the fibrin formation is the result of a cascade, so there is a series of events.1723

One enzyme activating another, activating another, that culminates in the formation of fibrin to reinforce that initial plug formed by the platelets.1729

You do not need to know the whole long complicated clotting cascade, but I am going to just talk about the last steps that are important steps.1740

So, if you jump in later in the cascade, one thing you will see is that prothrombin, which is inactive, becomes converted to thrombin.1749

And this is the active form, so I will put a star. That is the active form.1759

Thrombin, then, acts on fibrinogen, which is the inactive form of fibrin, and it activates fibrin. It converts it to its active form, which is fibrin.1766

That fibrin is a filamentous thread-type structure, and it clumps up to form a clot at the site of the damaged vessel wall.1784

It reinforces that initial clot formed by platelets.1793

Now, these are floating around in their inactive form, which prevents clotting from just occurring at random times, which would be disastrous.1797

However, there are also anti-clotting factors that circulate in the blood.1807

So, the clotting cascade does not just occur randomly. It has to be triggered.1813

And platelets release clotting factors. The damaged cells can release clotting factors, and there are clotting factors in the plasma.1818

A deficiency in clotting factors leads to a disorder known as hemophilia, so hemophilia is a result of a deficiency in a particular clotting factor.1828

And individuals with hemophilia are at risk for bleeding.1839

So, even a minor injury could be more serious in an individual with hemophilia because they are not able to stop the bleeding.1846

And they may need to be given these factors.1852

A thrombus is another name for a blood clot, so a thrombus is a blood clot.1856

And when we talk about the heart, we are going to talk about the role that blood clots can play in causing a heart attack.1861

Before we do that, let's talk about the final component of the circulatory system, which is the heart.1870

Amphibians and most reptiles have a three-chambered heart. Mammals and birds have a four-chambered heart, and that is what you see here.1880

It consists of two atria and two ventricles.1889

One side of the heart, the right side, is responsible for pumping the deoxygenated blood into the lungs.1895

The left side of the heart pumps the oxygenated blood to the systems of the body.1904

So, there are two different circuits. This is a double circuit system.1911

There is the pulmonary circuit, and there is the systemic circuit.1916

So, here, we have the right side of the heart, so if the person is facing you, this is the right atrium, the right ventricle, the left atrium and the left ventricle.1927

Let's go through the structure and then, the pathway of the circulation of the blood through the heart.1946

The heart is about the size of fist, and so here, I have the clenched fist, and then, here on the right side, we have the right atrium.1952

Between the right atrium and the right ventricle is a valve. It prevents backflow.1961

So, the blood from the atrium enters the ventricle, and we do not want it flow backwards into the atrium; so this valve prevents that.1968

And this valve is called the tricuspid valve.1974

Here, on the left side of the heart, separating the left atrium and the left ventricle, is another valve called the mitral valve.1981

These valves separating the atria and the ventricles are known as the atrioventricular valves.1997

Another name for the tricuspid valve would be the right AV valve and over here, we have the left AV valve,2008

tricuspid or right AV valve and the mitral valve or the left atrioventricular valve.2021

Now, the ventricles, the walls are thicker than the atrial walls, and in particular, the left ventricle is very strong and very forceful.2028

There are also valves between the heart chambers and the major vessels.2042

So, let's look at these different vessels. Here, if we have the lungs up here, then, blood is going to be oxygenated in the lungs.2050

And it is going to return to the heart via these pulmonary veins, so right here are the pulmonary veins.2062

Blood is coming from the lungs. It has picked up oxygen.2076

It enters the left side of the heart. The left atrium flows into the left ventricle and then, goes to the body.2078

This is actually oxygenated blood, so let me put that in. Let's actually change these.2088

This right here, this is oxygenated blood, and it is leaving the left side of the heart via the aorta.2095

Now, once the blood flows to the body, it is going to drop off its oxygen.2105

It is going to pick up waste products, and this deoxygenated blood is going to return to the heart.2111

It is going to enter the left side of the heart via the superior and inferior vena cava.2117

These two vessels are the vena cava and the superior and inferior vena cava.2123

The superior vena cava drains the upper half of the body: the trunk, the head, the upper extremities.2135

It returns the blood from the upper half of the body. The deoxygenated blood is going to go in here and here.2143

The lower half of the body is drained by the inferior vena cava.2151

The blood will go into the right side of the heart - the right atrium, the right ventricle - and then, to the lungs via this pulmonary artery.2156

This structure is the pulmonary artery, this structure right here.2171

So, tracing this route, let's start in the lungs.2184

The blood is in the lungs. It picks up oxygen, and it returns to the heart via the pulmonary veins.2189

So, this is oxygenated blood, so they are carrying oxygenated blood.2199

Remember, I mentioned that there are some veins and some arteries that are not what you would expect in terms of the type of blood they carry.2203

Most veins contain deoxygenated blood. The pulmonary veins are carrying oxygenated blood from the lungs to the left side of the heart.2210

That blood is going to pass through the left atrium, the mitral valves, enter the left ventricle and then, be pumped out of the aorta to the body.2221

So, it is going to the body from here.2233

Blood goes to the body. Body cells take the oxygen, give the blood the CO2 and waste products.2237

That blood from the body enters the superior and inferior vena cavas. It is deoxygenated blood.2245

It enters the right atrium, passes through the tricuspid valve into the right ventricle and then,2252

is pumped out via the pulmonary artery to the lungs to pick up oxygen again.2261

So, for the right side of the heart, we have the blood being pumped to the lungs,2269

the pulmonary circulation and then, the systemic circulation on the left side of the heart.2274

The left side of the heart pumps the blood to the body.2278

A heart attack or a myocardial infarction is the death of the heart muscles.2284

So, what happens is the aorta carrying oxygen and blood branches of into what is called...2290

It has some branches that come of it that form the carotid arteries.2296

And the carotid arteries supply the heart with blood, with oxygen, with oxygenated blood.2300

So, the carotid artery is the responsible for supplying the heart with oxygen.2306

If the heart does not get enough oxygen, the result is a myocardial infarction, which is damage or death of the heart muscle.2311

Also, it is more commonly known as a heart attack.2324

Now, one risk factor for a heart attack is a disease called atherosclerosis, and this is a condition in which plaque builds up in the arteries.2328

Plaque consists of fatty deposits, and these build up in the walls of arteries.2346

So, if you were looking at a cross-section of the artery, and there were plaque deposits in it, then, these would narrow the artery.2351

If the blue is plaque, and there are these deposits, it is going to narrow the artery, so it is going to decrease the blood flow.2358

Then, when a serious problem can occur, even more serious is if the plaque ruptures.2365

If the plaque ruptures, a piece of it breaks off, and when a piece of plaque breaks off, it actually triggers thrombus formation.2370

So, a clot to form on the plaque, so now, you have this piece of ruptured plaque. It has got a clot on it, and it is floating through the bloodstream.2379

And it is floating through damaged arteries that are already narrow.2391

And what can happen is, the already narrow, now, you have this clump floating through.2395

And it can actually lodge in an artery, block it and cut off the blood supply.2399

If this occurs in the heart, the result is the heart muscle, which needs a lot of oxygen, is not getting oxygen, and it can be damaged. It can die.2404

And that is the pathophysiology underlying a heart attack.2414

We have looked at the anatomy of the heart, the blood flow through the heart, and I just want to emphasize these two circuits.2422

So, the system in mammals is known as double circulation, and some animals have a single circuit.2430

Mammals have a double circuit, so a double circuit system or double circulation.2438

There are two circuits that the blood travels through. I am going to put up here it is the pulmonary circuit, and below is the systemic circuit.2445

And the pressure drops quite a bit when the blood passes through the capillaries. These are capillaries.2457

But, since the blood returns to the heart and is pumped again before it goes to the second set of capillaries, it raises the pressure back up.2464

This is a very effective system in maintaining high pressure throughout.2473

And this is important for mammals because they are very active. They have a high metabolic rate.2479

They need a very good supply of nutrient and oxygen.2483

Right here, we have the right side of the heart, and here is the left side of the heart. This is the lungs up here.2489

What is happening is that the right side of the heart is going to pump the deoxygenated blood into the lungs.2498

And then, in the lungs, gas exchange will occur. The blood will become oxygenated again and then, drain into the left side of the heart.2508

The left side of the heart, the systemic circulation, the left ventricle, will pump blood out through the aorta to the body tissues and organs.2523

And in the capillaries of the body tissues and organs, the oxygen will be dropped off and CO2 will be picked up.2535

So, then, that blood becomes deoxygenated and returns to the right side of the heart, so there are two circuits in the mammalian system.2547

The cardiac cycle refers to the alternation of contractions and relaxation that occurs in the heart.2556

This rhythmic cycle of contracting and relaxing of emptying the chambers during2564

contraction and filling the chambers during relaxation is known as the cardiac cycle.2570

One round, so the cardiac cycle, one cycle equals one round of filling and emptying of the heart chambers or one round of relaxing and contracting.2577

This would be equal to one heartbeat, so the heart beats.2600

What we call one heartbeat is one cycle of the heart contracts,2608

pumps the blood out, empties the chambers, relaxes and allows the chambers to fill again.2613

Some terminology you should be familiar with, systole is the part of the cycle when the heart contracts, so this is called systole.2619

Diastole is the part of the cycle when the heart relaxes.2637

So, during systole, the heart contracts, and blood is emptied. The chambers of the heart are emptied.2649

During diastole, relaxation occurs. The heart chambers fill back up.2659

The average heart rate in an adult, so average heart rate, is about 70 beats per minute, and you might just see it written as bpm- beats per minute.2665

During that minute, if the heart rate is 70, the heart pumps about 5 liters of blood.2683

And this is equal to the volume of blood present in an average-sized adult's body.2692

So, the total volume of blood in someone's body is pumped by the...that amount is pumped by the heart every minute.2697

Blood pressure: the typical blood pressure in an adult is about 120/80 with variations, but this is typical or normal.2707

It is considered normal around in this range.2718

And this top number is known as the systolic blood pressure. This is the pressure in the arteries during the contraction of the heart, so during systole.2721

This bottom number is the diastolic blood pressure, and it is the pressure in the heart when the ventricles relax.2734

Remember that it is the thick walls of the artery that maintain the blood pressure during diastole.2744

During systole, the walls of the arteries are pushed out by the pressure of the blood inside the vessels after the ventricle contracts.2749

When the ventricles relax and are refilling, the arterial walls spring back in, and that helps to maintain the blood pressure.2757

The second thing we are going to talk about now is how the heart rate is set and the maintenance of a regular rate and rhythm in the heart.2767

Heart muscle/cardiac muscle is inherently contractile. It has the inherent ability to contract.2777

If you take some heart muscle, put it in a test tube or an additional lab and looked at it, it contract. It has the ability to contract.2784

However, you cannot have just all these cells contracting at their own rate.2795

The heart would not move in a coordinated manner. It would not be able to pump blood.2800

If that happens, it is called a dysrhythmia, and it can even be life-threatening, so we need a way to maintain the regular coordinated rhythm of the heart.2805

And what the heart has is a structure called the SA node. This stands for sinoatrial node, and this is the heart's pacemaker.2816

It is the heart's natural pacemaker. It sets the heart rate.2830

So, this is a schematic diagram of the heart, but the SA node is located up here in the right atrium, just to give you an idea.2841

And it generates an electrical signal that travels through the walls of the atria.2850

And then, again, this is showing the right and left, sort of, separated out.2859

But in reality, there is the wall of the right and left atria that are next to each other.2863

And there is another structure, and it is called the AV/atrioventricular node.2868

And the signal gets delayed very slightly at the AV node, and what this allows is for the atria to contract slightly before the ventricles.2876

And the reason is you want to have the atria empty so that the ventricles can be filled before the ventricles contract.2886

So, the signal originates at the SA node. It is transmitted through the two atria to the AV node.2894

There is a little delay there while the atria is contracting. Blood flows into the ventricles, and the signal continues on.2901

So, it continues on through the ventricles.2910

And there are structures in the ventricles, the Purkinje fibers and the bundle of His, through which the signal is transmitted.2913

The signal travels from the SA node to the AV node through the bundle of His,2934

through bundle branches and via these structures right here, throughout the ventricles.2943

From the atria, SA node, a little pause in the AV node, then,2951

through structures in the ventricle that transmit the electrical signal so that the ventricles contract.2955

Because these electrical impulses, they are also detected elsewhere in the body.2962

These electrical impulses travel through body fluids and out to the skin, so we can actually detect the electrical impulses of the heart out at the skin.2967

And you have probably heard of a test called an EKG or sometimes ECG. This stands for electrocardiogram.2977

And in this test, what we do is place electrodes on the skin.2986

And that allows us to detect these electrical signals and to assess the functioning of the heart.2993

Now, although the SA node sets the rate of your heart. As you know, your heart rate can be modified.3001

If you are exercising, if your running, your heart rate speeds up. If somebody scares you, your heart rate speeds up.3008

If you are just resting, your heart rate slows down, and this is because the heart rate is affected by the autonomic nervous system.3013

The autonomic nervous system is responsible for involuntary actions.3023

The autonomic nervous system has two major branches to it: the sympathetic and parasympathetic systems.3033

The sympathetic nervous system speeds the heart rate up.3050

This sympathetic nervous system has to do with the fight or flight response, and it helps to speed the heart rate up; so this is increased heart rate.3056

Parasympathetic, if you are at rest, that will help to slow your heart rate down- decreased heart rate.3069

Hormones such as epinephrine or norepinephrine, that we will talk about in the endocrine section, also affect heart rate.3077

Now that we have covered the component of the circulatory system, the flow of blood through the heart, the components of blood,3087

I am going to talk in more depth about how oxygen is transported through the blood as well as how CO2/carbon dioxide is transported through the blood.3094

Remember that red blood cells contain hemoglobin, and hemoglobin is the carrier protein for the oxygen.3103

It is what allows oxygen to be efficiently and effectively conveyed through the blood.3111

Oxygen actually has a low solubility than water.3118

It would be impossible to deliver enough oxygen to body tissues if we had to rely on just dissolving it in plasma.3122

In fact, only a few percent of oxygen is dissolved in plasma. The other 97% is carried by the hemoglobin.3130

Hemoglobin belongs to a group of proteins that are called respiratory pigments.3139

So, another respiratory pigment is hemocyanin.3147

Hemocyanin contains copper, whereas, hemoglobin contains iron, so we are going to talk about hemoglobin in depth.3154

Just to briefly talk about hemocyanin now, hemocyanin is found in the hemolymph of some arthropods and some mollusks.3164

Now, we talked about the fact that arthropods, for example, usually just deliver oxygen via the tracheal system directly to cells.3184

However, there are some arthropods as well as some mollusks that use the hemolymph as an important component to deliver oxygen to cells.3193

And the carrier protein that they use is hemocyanin.3201

The hemocyanin is not contained in cells in the blood. It is just in the blood fluid.3203

And this is a respiratory pigment, and it is actually a bluish-colored pigment.3209

Now, what we are mostly going to talk about is hemoglobin, and that is the respiratory pigment that is found in mammals and that is found in us.3214

Vertebrates use hemoglobin as their respiratory pigment. It is a protein consisting of four subunits.3223

Here is shown 1, 2, 3, 4 subunit. Each subunit contains heme, and within the heme is an iron molecule.3232

Each iron molecule can bind an oxygen, so one hemoglobin molecule can bind four oxygens.3245

Red blood cells are packed full of hemoglobin. Remember they do not even have a nucleus.3254

And they do not have a nucleus, which allows them to have even more room to just pack full of hemoglobin.3259

Each hemoglobin is bound to four oxygen, so red blood cells are very efficient at carrying oxygen from one site to another.3265

Now, this structure is very closely related to the function. Because it has four subunit, it actually allows for an allosteric interaction.3273

Remember that an in an allosteric interaction, what occurs in one part of a molecule can affect the conformation, can affect another part of the molecule.3283

And in fact, hemoglobin demonstrates cooperative binding, so hemoglobin demonstrates cooperative binding of oxygen.3292

What happens is the binding of oxygen to the first subunit causes a conformational change that makes it easier for the second subunit to bind oxygen.3305

That makes it easier for the third subunit, and it makes it easy for the next subunit.3315

So, it is toughest to get that first subunit to bind, but once that is bound to oxygen, binding is easier for the remaining subunits.3321

Now, this can be understood a little bit further by looking at a curve called the oxygen-hemoglobin dissociation curve.3331

And this is something you should be familiar with and that you should understand.3341

So, we are looking at this graph, and this graph has a sigmoidal or S shape.3346

The graph shows the percent saturation of hemoglobin with oxygen, so the percent of hemoglobin that is bound by oxygen.3353

And it is comparing it versus the partial pressure of oxygen in millimeters of mercury.3367

Over here, we have very low partial pressure of oxygen, and it is starting out at no hemoglobin being bound to oxygen.3373

This curve is actually flatter at very low partial pressures of oxygen, and then, the curve gets steep. It flattens out again.3385

So, exaggerating it some more, it would be an S-shaped curve.3394

Now, this has to do with that structure of hemoglobin with the four subunits and the cooperative binding.3397

At very low partial pressures, most of the hemoglobin is unbound to oxygen, and if I raise the oxygen a little bit, yes, some of the hemoglobin will bind.3404

But it is difficult because it is the binding of that first subunit, and it is difficult for that to occur.3415

Getting that first subunit bound is difficult, so a lot of the hemoglobins are not bound at all, and then, some of them start to bind a very first subunit.3421

However, if I raise the oxygen partial pressure even more, I take it up to, say, 20 here, I see that the curve is very steep.3430

And that is because once that first subunit is bound, it is easier for the second.3438

When the second is bound, it is easier for the third, so once we get past the first subunit binding, the curve becomes much steeper.3443

So, in this physiological range where most of our body tissues are, if you increase, say, I am here at 20,3452

and about 35% hemoglobin saturation with oxygen, if I increase to 30, that percent saturation goes to 60.3461

So, all this increase in binding of hemoglobin to oxygen by this slight increase in the partial pressure of oxygen.3475

At very low partial pressures, the curve is not steep. In the middle, the curve is steep, and then, the curve flattens out.3485

And the reason it flattens out is saturation has been reached.3491

I can add more and more and more oxygen, but the problem is there is no more hemoglobin sites left to bind oxygen.3495

So, at a certain point, adding oxygen is not going to increase the saturation. It is maxed out.3504

So, this is the shape of the curve.3509

And you should understand that this sigmoidal shape has to do with the four subunits of hemoglobin and the cooperative binding.3511

Now, low partial pressures of oxygen would be in active tissue.3520

So, if you look at your muscles when you are working out, they are using up a lot of oxygen.3527

Because they are undergoing aerobic respiration, they need to make a lot of ATP, a lot of energy.3532

So, they are going to use up oxygen that have low partial pressure of oxygen.3537

In the lung, there will be a high partial pressure of oxygen.3541

And the affinity of hemoglobin for oxygen can change based on conditions.3548

And this allows the hemoglobin to deliver oxygen where it is needed and pick up oxygen where it is needed.3555

One condition that affects the affinity of hemoglobin for oxygen is pH.3565

So, if we look at pH, a lower pH decreases the affinity of hemoglobin for oxygen.3573

A lower affinity can be looked at as the hemoglobin will let go of oxygen more readily.3593

Hemoglobin lets go of oxygen more easily, so what does this mean?3601

First of all, think about where pH is low. Recall that pH is going to be lower in metabolically active tissues.3610

I discussed this is the respiratory lecture, and I am going to discuss it again in a minute in more detail.3621

But for right now, just recall that in blood cells, carbon dioxide and water combine to form carbonic acid, which forms bicarbonate and hydrogen ion.3626

So, in a muscle or a body tissue that is very metabolically active, it is using oxygen, it is generating CO2,3640

this reaction will be pushed to the right with the result of increased hydrogen ions and therefore, decreased pH.3647

In metabolically active tissues, the pH is low. The result is what we call a shift to the right of this curve, so this curve is going to change.3659

At low pH, this will be the curve: shift to the right.3681

This shift to the right, under certain conditions, is called the Bohr effect or the Bohr shift.3688

Let's look at what this means. Let's say I looked at here a PO2 of about 30, and I say "Alright".3700

At a PO2 of 30, I go up to my first curve, and hemoglobin saturation is about 60%.3714

Now, the curve has shifted to the right. At the same partial pressure of oxygen, 30, hemoglobin saturation is only 40%.3723

That means 20% has been let go. Instead of 40% or instead of 60% saturation, we only have 40%, so all of this has been let go.3736

Looking at it this way, it allows the hemoglobin to let go of oxygen or deliver oxygen to where it is needed.3752

And the reason for this is that the presence of these hydrogen ions changes the conformation of the hemoglobin molecule and gives it a lower affinity.3760

It does not bind as well to the oxygen.3768

This is how the red blood cells know "let go", or it helps them to let go of the oxygen.3770

So, when a red blood cell travels to the body, it arrives at a tissue that is in need of oxygen, and the pH there is low.3777

It will decrease its affinity for oxygen and let go of the oxygen and then, pick up CO2, go back to the lung.3786

In the lung, pH is higher, so pH is back up at 7.4; so in the lung, this curve is going to shift back to the left.3793

And what is going to happen in the lung, then, is at any given PO2, the hemoglobin is going to have a higher affinity for oxygen.3806

And it is going to grab oxygen, which is exactly what you want in the lung.3815

In the lung, you want a higher affinity of hemoglobin for oxygen, and so it will grab oxygen.3818

In the tissues of the body, you want a lower affinity of hemoglobin for oxygen so that it will drop the oxygen off.3825

If you look at curves for maternal and fetal hemoglobin, you will also see the differences in affinity here of hemoglobin for oxygen.3834

So, if I looked at a fetal hemoglobin curve, I am going to put it in black here, versus maternal, if this is fetal hemoglobin and the blue is maternal,3846

what the fetus needs to do is it needs to take oxygen from the mother to survive. That is where it has to get its oxygen.3859

So, at any given PO2, if I look here at 40, what I will see is that the maternal hemoglobin binds, say, for 75% saturated.3865

But, the fetal hemoglobin is 90% saturated, so the fetal hemoglobin has a higher affinity for oxygen than the maternal hemoglobin.3876

Before going on, I also want to note that another factor that can cause a shift to the right, I said, it is caused by low pH.3886

Another thing that occurs in active tissue is the temperature increases.3896

If you are running, the temperature in your muscles is going to increase.3900

So, increased temperature also triggers the shift to the right because it is another signal that that tissue needs oxygen.3903

There is another hemoglobin-binding molecule called myoglobin.3914

Myoglobin has only one subunit. It does not have the four subunit structure.3919

So, it does not demonstrate this sigmoidal shape. It is just a linear graph for hemoglobin binding.3926

However, one thing about myoglobin is that it has a higher affinity for oxygen than hemoglobin, and because of this, it binds oxygen very effectively.3931

And there are marine mammals like seals that can dive and stay under water for 30 minutes even hours.3942

And what allows these mammals to do it when humans certainly cannot do this is that these mammals have large stores of myoglobin in their muscles.3950

So, stores of myoglobin allow certain marine mammals to remain submerged for long periods.3960

And it provides a store of oxygen for these mammals during that time.3980

Alright, we have talked about oxygen transport, and now, I am going to talk more about CO2 transport.3992

So, the blood is traveling through the capillaries. It arrives at the body tissues.3999

It drops off its hemoglobin, and it picks up the CO2 from those cells.4006

There is a small amount of the CO2 that just dissolves in the plasma and is transported that way, so that is one way that transport occurs.4011

A second way that CO2 is transported is it binds to hemoglobin.4020

A CO2 can actually bind with the amino group on hemoglobin peptide, but these are not the major ways a CO2 is transported.4026

The major way that oxygen is transported is binding within the hemoglobin molecule.4035

But, for CO2, most transport is actually in the form of bicarbonate ion.4039

So, what happens is a red blood cell goes to the body tissues, drops off its oxygen, so here is a red blood cell.4046

The oxygen and this is the body tissues, and there is the capillary wall, of course.4054

It has diffused past the capillary wall into the fluids running the tissue and then, into the cells.4063

So, the oxygen is going to diffuse out, be dropped off to the body tissues. Then, carbon dioxide from the tissue is going to enter the red blood cell.4068

In the red blood cell, this CO2 will recall the reaction where it is going to combine with water. It is going to form carbonic acid.4087

And this reaction is reversible and then, bicarbonate ion and hydrogen ion.4102

The conversion of CO2 and water to carbonic acid, H2CO3, is catalyzed by the enzyme carbonic anhydrase.4110

So, the result here is that CO2 is taken up, and reaction occurs that converts this CO2 plus water eventually to bicarbonate and hydrogen ion.4130

So, what happens to this? Well, the bicarbonate can leave the cell and enter the plasma, and it becomes part of the plasma buffering system.4147

It serves as a part of the buffering system and also as a means of transporting this carbon dioxide in the bloodstream.4160

How does this serve as a buffering system? Well, let's say that the pH is too high.4171

So, if the pH is too high, this means we need more hydrogen ion.4180

What can happen, then, is this reaction will go the opposite direction. Actually, no, it will go in the forward direction.4187

If we need more hydrogen ion, then, more CO2 will combine with water to form carbonic acid. That is H2CO3.4197

And so, CO2 will combine with water to form carbonic acid, and that will, then, go on to form bicarbonate and hydrogen ion.4216

So, this is if the pH is too high.4241

Now, let's say the blood pH is too low. We need to decrease this level of hydrogen ion.4243

So, now, bicarbonate and hydrogen ions will react to form carbonic acid, which will, then, dissociate into carbon dioxide and water,4252

thus, lowering the concentration of hydrogen in the blood and raising the pH back up.4265

You can see this reaction going one way or the other helps to buffer the blood and keep the pH within a narrow range.4272

Once this blood travels to the lung, what is going to happen in the lung is that CO2 is going to diffuse into the lung.4281

So, the CO2 is going to go into the lung, which is going to pull this reaction back to the left.4292

As we draw the CO2 off, hydrogen ions will combine with bicarbonate to form carbonic acid and then, carbon dioxide and water.4300

So then, more carbon dioxide can diffuse into the lung.4313

This reaction also helps to deliver the CO2 into the lung once the red cells and the plasma reach the lung, OK?4318

Important points are that the majority of carbon dioxide is actually transported in the blood in the form of bicarbonate ion.4330

You should also be familiar with this reaction in which CO2 and water combine to eventually form bicarbonate4340

and hydrogen ion and the fact that this allows for a buffering system in which to decrease the level of4347

hydrogen ions as needed if the pH is too low or increase the hydrogen ion concentration if the pH is too high.4357

OK, now, we are going to talk about some examples using the material from the circulatory system.4368

Example one: trace the pathway of blood through the circulatory system by placing the structures below in the correct order.4376

Begin with the oxygen-rich blood as it leaves the lungs to return to the heart.4384

We are starting in the lungs, so how is the oxygen-rich blood from the lungs brought back to the heart via the pulmonary veins?4391

So, this is a vein or veins that actually carry oxygenated blood.4404

We start out in the lungs. From the lungs, blood travels via the pulmonary veins, so I have used this one.4409

Oxygenated blood returns to the left side of the heart, so that would be first the left atrium.4422

The blood will pass through the mitral valve into the left ventricle.4430

When the left ventricle contracts, it pumps blood into the systemic circulation, and that occurs through the aorta.4437

The blood is, then, going to go into the body tissues, drop off oxygen, pick up CO2 and then, enter veins to return to the heart.4449

In the upper part of the body, the superior vena cava drains this deoxygenated blood into the heart.4460

In the lower half of the body, it is the inferior vena cava, so we are just going to put "vena cava".4468

So, this blood is now deoxygenated. It is going to drain into the right atrium.4475

We used right atrium. We used vena cava.4487

Then, from the right atrium, the blood will go to the right ventricle.4491

It is deoxygenated, so it is going to be pumped from the right ventricle through the pulmonary artery to the lungs to complete the cycle.4495

So, this is the correct order: lungs to the pulmonary veins to the left atrium, left ventricle,4510

aorta, vena cava, right atrium, right ventricle and then, finally, pulmonary artery.4517

Example two: which veins carry oxygenated blood?4526

Well, from what we just discussed, you know that the pulmonary veins carry oxygenated blood from the lungs to the heart.4531

What is the name of the structure that functions as the pacemaker for the heart? That is the sinoatrial node, very commonly known as the SA node.4553

What are the cell fragments in the blood that function in clotting called? These are the platelets.4568

These are cell fragments found in the blood.4576

Describe the role of vasodilation and vasoconstriction in thermoregulation.4584

Recall that vasoconstriction is constricting of the blood vessels, so the diameter becomes smaller.4591

In vasodilation, blood vessels dilate. Their diameter becomes larger.4597

In the cold, vasoconstriction of superficial vessels occurs.4602

The result is decreased blood flow through those vessels, and then, the result is decreased heat loss via heat transfer through the skin.4619

Heat triggers vasodilation of the superficial vessels. The result is going to be a decrease in the vessel diameter or an increase.4636

Excuse me. Vasodilation is going to increase the diameter of the vessels.4654

The result is going to be increased blood flow through those vessels and increased heat loss through4660

heat transfer from the superficial vessels out in the environment, so this will cool the body down.4668

The result, then, increased heat loss, the body cools.4676

The opposite occurs with vasoconstriction. There is less heat loss through the skin, through the superficial vessels, and the result is the body warms.4681

And this helps us maintain our body temperature.4690

Hemoglobin, this dissociation curve is shown below. Sketch the expected curve following an increase in pH.4695

Think about what happens, the conditions, when pH is increased.4704

pH is decreased in active tissues. These are tissues that are using a lot of oxygen and generating CO2.4710

And what we want to happen is decreased hemoglobin affinity for oxygen.4721

So, the result is if pH is decreased, we get the shift to the right that we talked about.4728

However, in the lungs, pH is going to be increased. That would be an example of higher, higher pH.4736

And what we want to do is increase the affinity of hemoglobin for oxygen because we want the hemoglobin to take the oxygen from the lungs.4743

Therefore, there is going to be a shift to the left, so the curve is going to be shifted to the left.4757

So, taking a look at this just to check, shift to the left is correct.4768

At a partial pressure of, say, 30, in my original curve, there is about 55% hemoglobin saturation.4773

In my new curve at a partial pressure of 30, there is actually a saturation of more like 90%. This is a difference of 35.4789

That much more oxygen was grabbed. It was picked up, which is what you want.4806

So, the answer is that there would be a shift to the left, so the curve would look roughly like this.4810

That concludes this lecture on circulation.4816

Thank you for visiting Educator.com.4819

Welcome to Educator.com.0000

We are continuing our discussion of animal physiology with the topic of the digestive system.0002

As chemoheterotrophs, animals need organic molecules from food for both a source of chemical energy and as the building blocks to synthesize materials.0011

In order to obtain energy to make ATP, animals need to break down the chemical bonds in food.0024

In order to do this, an animal needs to ingest the food, then, digest it and finally, absorb it.0032

So, these are the three major steps in the digestive process.0041

There are two general types of digestion: intracellular digestion and extracellular digestion.0046

Intracellular digestion occurs within vacuoles, so vacuoles fuse with lysosomes.0058

And these contain hydrolytic enzymes that can break the bonds of the macromolecules like proteins so that they can be used by the cell.0066

Lysozymes break down the chemical bonds in the nutrients, and in some simple animals, digestion is entirely intracellular like this.0076

For example, sponges digest their food solely by the intracellular route.0089

And when we were talking about another group, not animals, but the protists, we talked also about digestion intracellularly.0097

Extracellular digestion is a lot of what we are going to be talking about today, and this occurs within the digestive tract/GI tract.0105

And the digestive tract consists of a tube, the gastrointestinal tract,0118

with different compartments in it, specialized compartments like the stomach and the small intestine.0123

So, we are going to go on now and first talk about different types of digestive tracts and then,0129

move on to focus in detail on the human digestive system.0134

The simplest type of digestive tract is a gastrovascular cavity.0139

Recall from the discussion on the diversity of life, when we talked about some simple animals like hydra and jellies,0144

the cnidarians, they have a gastrovascular cavity, so gastrovascular cavity, example would be jellies and hydras.0152

A jelly would use its tentacles to capture prey. It would draw that prey, then, into the gastrovascular cavity, which has only a single opening.0162

So, that is something important to know that the gastrovascular cavity has only a single opening.0174

The jelly will capture its prey. The prey will enter the gastrovascular cavity through a single opening.0179

And then, what happens in the gastrovascular cavity is that digestive enzymes are secreted into the cavity.0186

Digestive enzymes, they are secreted into the gastrovascular cavity, and there, digestion takes place.0197

There is no separate circulatory system for animals with the gastrovascular cavity because these nutrients just enter the cavity and then,0212

are broken down and diffuse directly into the cells.0223

Waste products exits through this cavity, as well, and there is only a single opening where nutrients enter and wastes exit.0226

Now, a complete GI tract or an alimentary canal has two openings.0235

One opening is for nutrients to enter. The other opening is for waste to exit.0252

Among the simplest animals with a complete GI tract are annelids, for example, earthworms and rotifers.0259

Of course, more complex animals such as mammals have a complete GI tract.0272

But, this is just talking about the simplest animals that developed a GI tract with two separate openings.0277

And we are going to focus now on the human digestive system.0285

But before I move onto that, I do want to mention that you are going to come across terms with some of the other digestive systems in animals0289

where there will be structures that are not found in the mammalian digestive tract, and one that you should be familiar with is crop.0297

A crop is a reference to a pouch that is found in the GI tract of annelids, insects, birds and some other animals.0305

And this is a place where food can be stored, so it is a pouch for storage of food prior to digestion.0316

We are going to focus now on the human digestive system. Mammalian digestive systems in general are similar, but some of this is particular to humans.0331

So, we are going to go ahead now and talk about an overview of the human digestive system.0341

And just looking and starting up at the top, what we have is the oral cavity, otherwise known as the mouth.0349

After the oral cavity, the food goes into the pharynx, continues on down into the esophagus, the tube that leads to the stomach,0361

enters the stomach, then, goes on to the small intestine, so on through the small intestine, leads to the large intestine here.0384

And then, waste exits the body.0414

In addition to this tract/tube with compartments, the GI tract, there are what is called accessory organs of digestion.0416

These are organs such as the liver, the gall bladder and the pancreas that play a role in digestion, but they are not part of the actual GI tract, of that tube.0426

As we discuss digestion, we are going to focus on three groups of nutrients and how they are broken down.0444

And those three groups are starch, fats and proteins.0449

As we talk about each section of the digestive tract, you should be thinking about what happens to starch at each point,0455

fats and proteins because they each take a little bit of a different path to digestion.0461

We are going to start up at the top with the oral cavity and the esophagus, so we will begin with the mouth.0468

Two things occur in the mouth, two major things: mechanical digestion and chemical digestion, and this is up in the mouth.0474

Mechanical digestion occurs by chewing.0487

Recall that mammals have several different types of teeth, and each of these is specialized to perform a different function.0490

In the front, mammals have sharp incisors and canine teeth.0496

What these do is they cut the food. They tear it.0501

Then, the food is processed by the premolars, those sit a little bit farther back behind the incisors and the canines, and the premolars shred up the food.0504

Finally, the molars in the back grind up the food.0514

The result is that by chewing up food, the surface area of the food is increased, and that allows for more efficient breakdown by digestive enzymes.0518

So, mechanical digestion occurs via the teeth. Chemical digestion occurs via enzymes.0529

And what is found in the mouth is salivary glands secrete amylase, salivary amylase.0536

And amylase hydrolyzes starch, so it breaks down starch. The starch is broken down to form polysaccharides and disaccharides such as maltose.0547

Proteins and fats are not chemically digested at this point. Their chemical digestion does not start until later on in the GI tract.0574

Another function of the mouth, and in particular of the tongue is to shape the food into a ball called a bolus.0584

So, the food gets shaped into this ball shape, and then, it is pushed down. It is swallowed and moved from the oral cavity into the pharynx.0591

And the thing about the pharynx is that it is a common pathway leading both to the airway right here, so this is the trachea, to the trachea.0604

And here, we have the esophagus. Therefore, in order to prevent choking, there is a flap called the epiglottis.0625

Here, you can see the epiglottis is open, so if a person is not in the middle of swallowing, then, the epiglottis can be open.0639

Then, air can go ahead and enter the trachea.0653

However, if somebody is swallowing, then, there would be a risk that food or liquid could enter the trachea and cause choking.0656

When we swallow, what happens is this flap - it is cartilage, it is a flap made of cartilage - of cartilage drops down and covers the trachea.0664

Now, whatever is ingested, food, liquid, whatever is in the mouth, and then, swallowed, it is going to be forced to go into the esophagus rather than0672

going into the trachea because if food or liquid goes into the trachea, obviously, it is going to interfere with your ability to breathe, get oxygen.0681

Even a small amount of food or liquid in the trachea would be a very big concern.0689

Once the food has been swallowed, and it passes into the epiglottis, it is moved into the stomach, and this occurs through peristalsis.0697

The epiglottis is made primarily of smooth muscle.0707

And what peristalsis is, is the rhythmic contractions of the smooth muscle that move food into the esophagus.0711

So, peristalsis is rhythmic contractions of the muscles of the esophagus.0721

At the top of the esophagus is a region of striated muscle, and this region functions as an esophageal sphincter.0725

This one is called the upper esophageal sphincter or UES, and when we are not swallowing, this contracts and closes off the esophagus.0735

When a person does swallow, so during swallowing, then, the epiglottis protects the airway.0755

And the esophageal sphincter relaxes to allow the food to enter the esophagus.0761

Alright, so, we are at the point where food has been processed by the mouth. It has been swallowed.0768

It is being pushed into the stomach via peristalsis.0772

Now, in the stomach, a lot of things occur.0777

For one thing, the stomach churns, and this churning motion helps to mix up the food and also mix digestive enzymes, gastric juices, in with the food.0784

So, to understand the stomach, you need to understand its structure, what it secretes and the functions of the enzymes that it secretes.0795

Food, the bolus, goes down the esophagus.0806

And then, it has to pass through a sphincter at the opening of the stomach called the lower esophageal sphincter.0809

This is also known as the cardiac sphincter.0828

The bolus of food, then, passes through the lower esophageal sphincter and enters the stomach.0842

And the stomach has several functions. It is a muscular compartment, and it functions to store the food temporarily.0847

It functions to break down the food, digest the food and to kill bacteria that are present in the food that we eat.0859

Gastric glands secrete gastric juices, and there are a couple types of cells in the gastric glands; and that is what is discussed up here.0873

The parietal cells maintain the acidic environment of the stomach, so what happens is hydrochloric acid is secreted from the parietal cells.0890

And the function of hydrochloric acid is to kill bacteria that might be present in the food.0902

The second major type of cells are chief cells, and chief cells secrete pepsinogen. This is a precursor to pepsin.0910

The acid, HCl, converts pepsinogen to pepsin.0918

Once some pepsins have been made, that pepsin can go on and convert even more pepsinogen to pepsin.0923

What is pepsin? It is a protease.0930

I talked about amylase starting the digestion of starch up in the mouth, and once the food enters the stomach, the chemical digestion of protein begins.0932

And it begins with pepsin hydrolyzing the proteins to polypeptides.0941

There are also mucus cells present in the stomach, and as you can imagine, their job is to secrete mucus.0949

Now, why would we need to have mucus in the stomach? Well, this mucus layer protects the lining of the stomach.0957

Because of the HCl secreted by the parietal cells, the pH in the stomach is very low. It is typically between 2 and 4.0964

And if there was no protection, the acid would just eat away at the stomach lining.0974

And in fact, when there is a breach in the mucosal layer, an ulcer forms.0979

If there is a part of the lining where it is not protected by mucus, then,0985

that would be a risk factor to form an ulcer or essentially a sore in the lining of the stomach.0989

Something interesting that was discovered maybe a decade or so ago or maybe even longer is that a bacteria plays are role in ulcers.0996

So, an ulcer is in part an infectious disease.1004

A type of bacteria called Helicobacter pylori or H. pylori, infection with H. pylori contributes to ulcer formation.1008

And so, antibiotics are actually one treatment for an ulcer.1019

Now, since the environment in the stomach is acidic, pepsin actually works best in an acidic environment.1025

And this is in contrast to most of the enzymes in the body.1034

Most of the enzymes in the human body work best at a pH of around 7.4. However, pepsin is an exception.1036

So, it is present in the stomach, and it is active at this higher or at this lower pH.1046

We have gone through the major functions of the stomach here, and it temporarily stores food.1054

And the food is passed slowly into the small intestine after digestion.1060

Food is digested chemically with pepsin, and bacteria are killed.1065

Once this food has been processed, it has been churned, it has been mixed with the pepsin, the pepsin has broken down a lot of the proteins,1072

it becomes a semi-liquid substance called a chyme, so this is digested food; and it is in a semi-liquid form.1080

And it is this digested food that is going to leave the stomach.1089

There is a second sphincter at the end of the stomach by the exit called the pyloric sphincter.1093

Chyme will exit through the pyloric sphincter and then, enter the small intestine.1104

That is the next section of the GI tract that we are going to talk about.1109

Now, in order to understand what goes on in the small intestine,1115

you have to be familiar with the pancreas because enzymes from the pancreas are secreted into the small intestine.1118

The small intestine is the major site of digestion. That is where much of the chemical digestion takes place.1123

And while the small intestine makes some of its own digestive enzymes, many of them are made by the pancreas.1130

The pancreas is an accessory organ of digestion, and we are going to talk about the various substances secreted by the pancreas.1136

Now, the pancreas is both an endocrine gland and an exocrine gland.1143

Endocrine glands secrete hormones directly into the blood stream. For example, the thyroid gland is an endocrine gland.1149

Well, the pancreas secretes insulin and glucagon directly into the bloodstream, and they are hormones.1159

So, we are not going to talk about that function now.1166

We are actually going to talk about the endocrine function of the pancreas when we discuss the endocrine system.1169

Right now, we are going to focus on the exocrine function of the pancreas.1175

Exocrine organs have ducts, and this means that substances are secreted through ducts.1179

So, there is a pancreatic duct, and the digestive enzymes are secreted into the small intestine through this duct.1192

We will start with the enzymes, and then, we will also talk about bicarbonate, which is another substance secreted by the pancreas.1206

Multiple enzymes are secreted. Let's start with amylase.1213

So, we talked about salivary amylase. Pancreatic amylase has the same function as salivary amylase.1216

It digests starch, and just like with salivary amylase, starch is broken down into polysaccharides and disaccharides.1222

Not all of the starches are digested in the mouth. Some of them make it down into the stomach still not completely digested.1237

So, they are broken down further here in the small intestine.1247

In addition, there are several proteases that are secreted by the pancreas into the small intestine.1254

And there are multiple different ones, and they have slightly different functions; but they all break down proteins.1262

And we talked about pepsin. Pepsin breaks down protein into polypeptides.1269

And here, we also have secreted from the pancreas, trypsin and chymotrypsin.1274

And what these do is they attack polypeptides at certain sequences, so they recognize certain sequences in a polypeptide.1287

And they break them down to smaller polypeptides.1295

The digestion of starches is continued here in the small intestine. The digestion of proteins is continued in the small intestine.1303

And the digestion of fats, we will talk about in a moment.1313

Now, another protease or actually peptidase is carboxypeptidase, which is produced by the pancreas.1316

And it breaks these peptides all the way down into amino acids.1328

So, as nutrients make their way through the GI tract, they are broken down into smaller and smaller components.1336

Now, we have not talked about fats yet because digestion of fats does not get started until the small intestine except for mechanical digestion.1341

Digestion of starches began in the mouth, continued on in the small intestine.1350

Digestion of proteins began in the stomach, continued in the small intestine.1355

Digestion of fats is just getting going now, and there are lipases that are secreted by the pancreas that hydrolyze fats to glycerol and fatty acids.1361

So, the breakdown of fats is initiated in the small intestine.1383

The liver also plays a role in the digestion of nutrients in the small intestine. The liver has many functions.1388

We are only going to focus now on the function that is related to digestion.1395

But, as we go through the different organ systems, I will mention the liver in different contexts.1400

For example, the liver produces clotting factors. The liver functions in the storage of sugar.1406

Here, though, what we are talking about is the fact that the liver produces bile.1412

Bile is a substance that is stored in the gall bladder, which is associated with the liver. The function of bile is to emulsify fat.1417

What do we mean by emulsify? Well, what bile does is it disperses fats into smaller particles.1431

So, there might a fat globule, and the bile is essentially a detergent that breaks that fat globule up into smaller particles.1438

What this does is it increases their...so, if you have this glob of fat, and then, bile acts on it; and it breaks it up into smaller particles,1450

this increases the surface area of the fats.1460

So, instead of one big glob, there are many small particles so that lipases can attack and break down the fats, as we just discussed.1465

We have talked about some of the accessory organs of digestion and the role they play in digestion in the small intestine.1478

Now, I am going to talk about the structure of the small intestine and enzymes produced by the small intestine, itself.1486

First of all, the small intestine is over 20 feet long, and it has three sections: the duodenum or duodenum, jejunum and ileum.1494

In the duodenum, what occurs is digestion.1504

The digestive enzymes I talked about from the pancreas as well as bile, these are all secreted here into the duodenum where digestion takes place.1506

The pancreas also secretes bicarbonate, so when chyme enters the small intestine, when it enters the duodenum, the chyme is acidic.1519

It has got the acidic gastric juices in it, and it enters. It is acidic.1530

That is neutralized by bicarbonates.1536

So, in addition to the pancreatic enzymes,1538

the pancreas secretes bicarbonate so that the pH in the small intestine is higher than the pH in the stomach so bicarbonate from the pancreas.1541

The jejunum and the ileum are not major sites of digestion. They are sites of absorption.1555

So, remember the three steps to digestion is ingestion, so the intake of food; digestion, the breakdown of food; and then, finally, absorption.1561

The digested nutrients need to be absorbed. They need to enter the animal's bloodstream.1570

The structure of the pancreas is very closely related to its functions.1576

In order to carry out the digestive and absorption functions, the small intestine needs to have a large surface area.1582

And if you look at the lining of the small intestine, and you took a close look; and you used a microscope and everything,1589

what you would see is small fingerlike projections called villi, and that is what this is. This is a villus.1595

Then, if you further looked closely at what these folds are constructed of, you would see more folding within the surface,1605

so folding upon folding, and these are microvilli.1621

So, we have villi, and then, within the villi, there are microvilli. Here is a close-up of the cells of the microvillus.1626

And what it shows here is what is called a brush border that extends into the lumen or the cavity of the small intestine.1641

And there are enzymes produced by these epithelial cells, by these cells lining the small intestine and1653

some digestion that are associated with this brush border, and some digestion takes place here, as well.1659

So, while it is very important to have the pancreatic enzymes being secreted into the small intestine,1665

some enzymes are actually produced by the small intestine, itself, by the epithelial cells of the small intestine.1670

So, in the duodenum, there are production of certain enzymes.1678

What happens in the duodenum is chemical digestion, and this is due to pancreatic enzymes.1683

And the pancreatic enzymes I mentioned were amylases, proteases and lipases. Bile also enters the duodenum and emulsifies fats.1695

In addition, in the duodenum, so chemical digestion due to pancreatic enzymes and intestinal enzymes,1708

enzymes that are produced within the small intestinal cells.1717

So, let's talk more about these intestinal enzymes- proteins, first of all.1724

So, we talked about proteins being broken down by pepsin in the stomach and then, further broken down by peptidases in the small intestine.1737

In addition, the intestines produce dipeptidase, carboxypeptidase and aminopeptidase.1747

The pancreatic enzymes break down the proteins into small polypeptides sometimes even into amino acids.1772

But, these additional intestinal enzymes ensure that proteins are broken all the way1781

down to the amino acid level because peptides cannot be absorbed into our bloodstream.1786

What has to happen is the proteins need to be digested all the way down from an intact protein to a1794

polypeptide to a smaller polypeptide, all the way down into the amino acid level to be ready for absorption.1800

Starches: starches are digested by amylase in the mouth, and amylase secreted by the pancreas into polysaccharides or even disaccharides.1808

But, in order to be absorbed, starches need to be broken all the way down into monosaccharides.1823

And if we just counted on the amylase, we would be left with a bunch of sugar that are disaccharides that we could not absorb into our bloodstream.1828

So, what happens is disaccharidases produced by the small intestine break down disaccharides into monosaccharides.1836

We take disaccharides and break them down into monosaccharides.1850

This is easier to understand if you know some of the examples.1854

For example, lactase and it ends in -ase. It is an enzyme.1857

What lactase does is it breaks lactose down, which is a disaccharide, into its monosaccharide form, and the same with maltase. It breaks down maltose.1862

And in fact, many people, when they reach adulthood, do not produce sufficient lactase to breakdown dairy products.1881

And that is why some adults cannot tolerate dairy products.1889

They will get upset stomach, GI symptoms, diarrhea, because the lactose sugars are not being digested in the small intestine.1894

Then, the glucose, the monosaccharides are not being absorbed. Instead, the lactose just pass on into the large intestine where the bacteria live.1904

And the bacteria have all these great nutrients, these sugars. They eat them and produce gas, so lactase insufficiency leads to lactose intolerance.1914

Now, what is happened then, in the small intestine, in the duodenum, is that they chyme has been neutralized by the carbonate secreted by the pancreas.1931

Pancreatic and intestinal enzymes have broken down starches to their monosaccharide form.1943

They have broken down proteins to their amino acid form, so what happens with fats at this point is the bile from the pancreas has emulsified the fats.1951

And the pancreatic lipases produced in the pancreas secreted into the small intestine have broken down these fat particles into glycerol and fatty acids.1971

And we are going to leave them at that point until we talk about absorption.1987

Now, the jejunum and the ileum are sites of absorption.1992

And I am going to talk about those right after we just sum up what we have talked about with the digestive enzymes.1998

So, we are going to leave it at the nutrients have been digested in the duodenum, and they are about to enter the jejunum,2004

and sum up the various digestive enzymes that you should be familiar with.2011

This table shows you where the enzyme is produced, the enzyme name and then, the action, what does it digest.2016

Site of production: mouth, specifically the salivary glands. The enzyme produced by the salivary glands, the enzyme in saliva is amylase.2024

Amylase digests starch into polysaccharides and into disaccharides.2037

So, here in the mouth, starches are already being broken down. You move into the stomach, and pepsin is produced.2044

This is a protease, and it hydrolyzes proteins into polypeptides.2052

The pancreas is a site of production. However, pancreatic enzymes are secreted into the small intestine.2057

Major categories here, amylase, like salivary amylase, digest starch into polysaccharides and disaccharides.2065

Trypsin, chymotrypsin and carboxypeptidase all digest proteins.2073

Trypsin and chymotrypsin digest proteins into polypeptides, whereas, carboxypeptidase breaks polypeptides all the way down to the amino acid level.2079

Right here, we have had starch, got started. Here, we have protein, starch again.2092

This is all protein, and this is all occurring in the small intestine and finally, now, fats.2107

Well, after being emulsified or dispersed by bile in the small intestine,2117

lipases attack the fats and break them down into monoglycerides or glycerol and fatty acids, so here, we have fats.2123

So, starch starts digestion up in the mouth. Proteins start digestion in the stomach, and fat digestion really gets started in the small intestine.2132

And just to mention at least briefly about DNA and RNA, DNA and RNA also need to be broken down.2143

And what happens is this actually begins in the small intestine where DNA and RNA are broken down.2153

I actually should say "DNA and RNA are broken down into nucleotides", and this is DNA nucleic acids.2161

DNA and RNA, their digestion begins in the small intestine.2173

Now, also in the small intestine are enzymes produced by intestinal cells. These are disaccharidases, which continue on the digestion of starch.2178

Now, we have left starch just based on pancreatic enzymes and oral cavity enzymes in the disaccharide form.2192

But, to be absorbed, the starch needs to be broken down all the way into monosaccharide form.2199

So, I am going to box in the form that can be absorbed by the intestinal cells.2205

Proteins: protein digestion started in the stomach. It is continuing on with these pancreatic enzymes and with small intestine enzymes.2214

And dipeptidases: carboxypeptidase and aminopeptidase are going to finish out the job of breaking down peptides into amino acids,2224

which can, then, be absorbed into the blood stream.2233

Nucleotidases and nucleosidases finish out the breakdown of DNA and RNA, of nucleic acids.2237

The nucleotides are further broken down into nucleosides, which are, then, broken down into nitrogenous bases and sugars by nucleosidases.2248

Meanwhile, the fats just stay in this form of monoglycerides and fatty acids.2260

And we will talk about what happens to those when they are taken up by the intestinal cells.2265

So, picking up in the latter part of the small intestine where digestion takes place, and these two segments are the jejunum and the ileum.2271

The small intestine has that very large surface area that we talked about with the villi and2290

the microvilli that increase its surface area greatly so that there is a large absorptive surface.2295

Now, you might recall in that picture, within that I showed you of a villus, within it were some blood vessels.2303

These capillaries within the villi take up the nutrients.2318

Here is the small intestine, and there is all these nutrients in it; and then, the cells here in the intestinal wall will take up the nutrients.2327

The nutrients will enter the capillaries within the villus, within these fingerlike projections called the villi.2336

The nutrients will be taken up, enter the capillary and then, enter the bloodstream.2344

These nutrients... well, actually the blood in the capillaries leaves the intestines and enters the hepatic portal circulation.2351

Nutrients are absorbed and enter capillaries, a capillary network within the walls of the intestine that transport nutrients.2362

And then, there are capillaries within intestinal walls, and then, these capillaries drain or enter into the hepatic portal circulation.2380

And it tells you it is hepatic meaning liver, and that circulation leads to the liver. This way, there is some regulation.2398

It is not just a bunch of nutrients at which it actually could include toxins, drugs, alcohol,2406

anything that has been ingested that should not just be dumped into the bloodstream.2412

There needs to be some sort of control, and the control is that these nutrients actually go to the liver first.2416

The liver is a very important site of detoxification, so the liver can detoxify drugs or alcohol. It can also pick up glucose for storage.2422

So, there is some regulation of nutrients entering the body because absorption in the jejunum2433

and ileum results in entry of nutrients into capillary that, then, go through the liver.2437

The blood goes through the liver, so it is important to know what form the nutrients are in when they are absorbed.2444

Recall that starches, by the time they have gotten through the early part of the small intestine, are in the form of monosaccharides.2453

And these monosaccharides are picked up by these capillaries and make their way to the liver.2463

Proteins are all the way in the form of amino acids.2470

They have been broken down into amino acids, and they are absorbed again via these capillaries.2474

Fats are a little more complicated.2480

Now, remember that when we left off with the duodenum, that the fats had been broken down into monoglycerides and fatty acids.2493

What happens is the intestinal epithelial cells take up the monoglycerides and fatty acids.2501

And there, these reform into triglycerides, so monoglycerides and fatty acids are taken up by the intestinal cells.2510

But, unlike, say, amino acids, let's say that just go into the capillaries and leave,2523

what happens is in these cells here, it is not just like amino acids pass through, go to the capillaries, leave.2527

Actually, inside these cells, some processes take place.2536

And what happens is the monoglycerides and fatty acids are taken up by intestinal cells and reconstituted or reformed into triglycerides.2543

So, they are reefed inside these cells, reformed in the triglycerides. Then, couple things are added to the triglycerides.2561

Cholesterol plus phosphates, phospholipids - excuse me, phospholipids, I meant to say - are added, and these form what is called chylomicrons.2570

So, fat is broken down into monoglycerides and fatty acids.2598

It is here in the intestine. These are picked up by the intestinal cells, reformed into triglycerides and then, packaged as chylomicrons.2603

These chylomicrons do not enter the capillaries. Instead, they enter what this is right here, which is a different type of vessel called a lacteal.2613

Chylomicrons enter the lacteals. What is a lacteal?2626

It is essentially a lymphatic capillary, so lacteals are lymphatic vessels.2631

So, instead of going straight in the capillaries and then, going into the hepatic portal circulation,2640

fats, in the form of chylomicrons, end up in the lymphatic circulation.2645

However, up near the neck, the lymphatic circulation joins the general circulation. It enters veins.2649

Eventually, these lacteals join the systemic circulation.2657

Therefore, the fats that have been digested are going to end up in the regular circulation, but they just take a little bit of different route.2669

They will end up in the venous circulation.2677

Now, we have gone from the point of ingesting food in the mouth,2681

digesting it in the stomach and small intestine and then, absorbing the nutrients in the small intestine.2685

Finally, the food enters the large intestine.2691

Although the large intestine has a greater diameter than the small intestine, it is not nearly as long.2696

And it consists of three parts: the colon, the cecum and the rectum.2702

The appendix is an outpouching of the cecum, and it is a vestigial organ. We have talked about that earlier on when we talked about evolution.2709

As far as we know, the appendix does not really serve a function in humans. It can cause problems, though.2721

It can become infected, impacted and result in appendicitis.2727

So, the three major parts: colon, cecum and rectum. The major functions of the large intestine are the absorption of water and salts.2733

Once the nutrients have been absorbed, there is waste products left, and there is also a lot of water left and salts.2746

And without the function of a large intestine, people would become very dehydrated because all that water would be lost.2754

By the time the waste finish their process through the large intestine, the waste is mostly solid.2763

The water has been reabsorbed back into the bloodstream.2771

Another function is the absorption of salts, the absorption of vitamins.2777

And in fact, in the large intestine, bacteria live. One of these bacteria is E. coli, and E. coli produce vitamin K.2783

They produce vitamin K in the large intestine, and that is absorbed and enters the circulation.2794

So, water, salts and vitamin K are all produced or retrieved here in the large intestine. Then, the waste exits the body via the rectum.2801

The digestive system is regulated by several hormones.2818

Without this regulation, there would be a lot of wasted energy because gastric juices would be produced when they were not needed.2823

And the pancreas would secrete enzymes when there is no nutrients around to digest.2829

So, this system of hormones triggers the various steps in the digestive pathway as they are needed.2833

Major hormones: gastrin, it is produced in the stomach. Its target organ is also the stomach.2841

And gastrin stimulates the production of the gastric juices that we talked about containing pepsin and acid.2848

And the release is triggered by the presence of food in the stomach.2857

So, you eat, food enters the stomach. That triggers the release of gastrin, which, then, stimulates the production of gastric juices.2863

Secretin acts on the pancreas and stimulates the production of pancreatic enzymes and bicarbonate into the small intestine.2870

Cholecystokinin, often just known as CCK, acts on several areas: the pancreas, the gall bladder and the stomach.2881

In the pancreas, it stimulates the release of pancreatic enzymes. It stimulates the release of bile from the gall bladder.2889

And it also slows down the stomach so that the food will remain in the stomach and get fully digested before moving on.2897

So, these are the major hormones that you should be familiar with.2906

Let's go ahead and do some examples now reviewing the digestive system.2911

Example one: how does the structure of an intestinal cell relate to its function?2915

The function of intestinal cells is, they have a digestive function. They produce digestive enzymes, and they also have an absorption function.2923

And these require a large surface area.2933

And recall that if you look at the lining of the intestine, what you are going to see is that it is lined by these foldings in the intestinal wall called villi.2939

And then, if you looked even closer, you would see, when you actually took one of these and did a close-up,2957

you would see that there is foldings called microvilli, and they are the cells all along here, so there are the villi.2965

And within those, the microvilli, so fingerlike projections called villi with further folds called microvilli that greatly increase the surface area.2976

In addition, associated with these are capillaries for absorption of amino acids and sugars.2985

There are also lacteals in here that absorb chylomicrons that absorb fats.2995

So, here is a very good example of structure and function being closely related.3003

What does role does bile play in the digestion of fats?3008

Remember that bile is produced by the liver, and it is stored in the gall bladder; and bile emulsifies fats.3011

This occurs in the small intestine, and emulsification means that the fats are dispersed into smaller particles.3021

The result is this is going to increase the surface area available to the lipases.3040

As I said, instead of having one big fat glob, there are many small ones.3050

And it is much easier, then, for the lipases to attack each of these than to attack this and not even be able to get up the substance in the center.3055

Example two: match the following terms to their descriptions.3067

No. 1, lipase: we just talked about lipases, a peptidase produced in the pancreas.3071

Well, this name tells you what it does. It is an enzyme with the lipids or fats, stores bile produced in the liver- that is not correct.3078

Site of production of hydrochloric acid in the stomach or an enzyme produced in the pancreas that hydrolyzes lipids.3089

So, E or D - excuse me - D is correct.3098

Parietal cells: a peptidase produced in the pancreas- that is incorrect.3103

Stores bile produced by the liver- not correct. Parietal cells are the site of production of HCl.3109

Gall bladder: gall bladder, remember, stores bile produced by the liver.3120

And finally, we have trypsin. Trypsin is one of the peptidases produced by the pancreas secreted into the small intestine.3127

Describe the digestion and absorption of starch beginning with its ingestion.3139

So, the starch is going to be ingested into the mouth, and in the mouth, there will be two types of digestion: 1. mechanical.3144

The teeth will break up the food including the food that is a starch and thereby increase its surface area.3157

And this occurs via the teeth, and it increases the surface area so that chemical digestion can take place more efficiently.3166

Chemical digestion in the mouth is via salivary amylase. This is secreted by the salivary glands via ducts into the mouth.3176

Amylase breaks the starch into polysaccharides and disaccharides.3187

The starch, then, enters the stomach where it is churned up and is sterilized by hydrochloric acid, but no major digestion of starch takes place there.3206

The next big step is in the small intestine. In the duodenum in the small intestine, additional chemical digestion takes place.3220

There are amylases secreted by the pancreas, which also break down starches into polysaccharides and disaccharides.3230

There are also disaccharidases, and these are produced by intestinal cells, and they break down these disaccharides such as maltose into monosaccharides.3240

Finally, in the latter parts of the small intestine, the jejunum and the ileum, the monosaccharides are absorbed.3263

They enter the capillaries and then, enter the hepatic portal system and then, go to the liver, so capillaries and then, eventually, to the liver.3278

Example four: what are two functions of the large intestine?3294

The large intestine is a site of absorption, so one function is the absorption of water. This is the major function.3299

A second function is the absorption of minerals, salts in the large intestine, so absorption is one function, two, waste storage.3308

Waste is stored prior to removal, and finally, it is a site of vitamin K production.3326

The E. coli in the large intestine produces vitamin K- site of vitamin K production.3331

Why is that the stomach lining damaged by the acid present in gastric fluids?3338

The pH in the stomach is about 2 to 4, which is a pretty low pH, and what protects it is mucus.3342

The mucosal glands/cells in the stomach produce mucus. This mucosal layer lines the stomach and prevents damage.3350

A breach in this layer can result in an ulcer.3361

That concludes this discussion of the digestive system at Educator.com3366

Welcome to Educator.com0000

In this section, we are going to continue our discussion of animal physiology with the focus on the excretory system.0002

The excretory system has two major functions.0010

One is the excretion of waste. The other is a role in homeostasis particularly osmoregulation.0013

Beginning first with its function as an excretory system, nitrogenous waste are produced by the breakdown of nitrogen-containing compounds,0024

for example, proteins and nucleic acids.0035

One product of this breakdown is ammonia, which is NH3. The thing about ammonia is it is very toxic in high concentrations.0040

So, there are some animals that directly excrete ammonia. However, many animals convert ammonia to less toxic substances and then, excrete those.0053

The less toxic substances that I am talking about are urea and uric acid. Those are the two main ones.0065

First, talking about animals that actually directly excrete ammonia, these are animals that live in the water,0070

so, animals that live in the water, that live in an aqueous environment directly0080

excreted by some animals that live in an aqueous environment- aqueous-dwelling animals.0090

This is because if an animal lives in the water, it is constantly exposed to very large amounts of water.0103

So, all this water coming in and bathing the animal dilutes out the ammonia during transport and during the excretion of ammonia.0109

So, the ammonia cannot concentrate and then, damage the animal cells.0119

Fish, for example, excrete ammonia through their gills, and a lot of water is passing through the gills; and it dilutes out the ammonia.0123

Simpler aquatic animals such as a hydra just excrete the ammonia through diffusion directly from their cells, directly into the water.0141

There are, however, some aquatic animals like sharks that do not secrete ammonia directly.0152

Sharks convert their ammonia to urea like many land-dwelling animals do.0158

So, let's now talk about the second common waste product, which is urea.0164

Many animals including mammals as well as annelids like earthworms excrete urea as their nitrogenous waste, and urea is much less toxic than ammonia.0171

Without this constant exposure to water, urea is a safer material to transport and excrete.0187

In mammals, urea is formed in the liver. In the liver, ammonia is converted to urea, which, then, leaves the body via the excretory system.0196

Another option for nitrogenous waste for animals is uric acid.0213

Reptiles and birds secrete or excrete nitrogenous waste in the form of uric acid. This is also less toxic than ammonia.0219

A major difference between urea and uric acid is that uric acid is poorly soluble in water.0231

In fact, uric acid has a consistency that is somewhat like paste.0243

And this is an advantage to animals like reptiles and birds that may have to go without water for a while. They live in drier environments.0247

So, instead of secreting urea in the urine and having to have this solute in a lot of water and lose a lot of water that way,0257

they can secrete uric acid from the body with very little water loss, so uric acid is an advantage for an animal that lives in a drier environment.0265

Now, the conversion of ammonia to either urea or uric acid has a cost, and that cost is energy.0275

This is an energy-requiring process, but it is a necessary one because the toxicity of ammonia would be a problem for animals,0283

especially land animals that do not have all this water diluting out the ammonia.0291

Excretion of nitrogenous waste is one major function of the excretory system, but another one is osmoregulation.0297

In many species, the second major function of the excretory system is a role in homeostasis.0306

Osmoregulation is a maintenance of a constant solute concentration in an organism.0313

So, to understand this, we are just going to go back to some basics of chemistry and talk about solutes and movement of water and osmosis.0319

Let's say I have a compartment separated by a semipermeable membrane meaning that water can cross this membrane but solutes, particles, cannot.0331

On one side, let's say I have a higher concentration of solute. The other side is going to be more dilute, a lower concentration of solutes.0344

This side is the hyperosmolar side. This side is hypoosmolar.0354

Water is going to move from the area of more water, or you could look at it either way.0369

You could look at it as the area of lower solute concentration, the hypoosmolar side to the hyperosmolar side to dilute this out.0379

Or you could look at it as water via osmosis is going down its concentration gradient0387

to an area of greater water concentration to an area of lower water concentration.0392

This is very similar to what we talked about when we talked about cells and we said hypotonic, hypertonic and talked about0399

water entering the cells if they were hypertonic, water leaving the cells if they were hypotonic relative to their environment.0407

So, here I am talking about just two different liquids, but it is the same idea with what we are talking about with a cell in a solution.0413

Osmotic pressure is a term that you should understand, and the solute concentration here is drawing water in.0423

The pressure that would needed to be applied to prevent this water from rushing in, to counteract,0434

there is a certain pull that these particles are essentially pulling water in.0441

Well, the pressure that you would need to counteract that is the osmotic pressure of the solution.0446

So, the osmotic pressure on this side is much lower because there are fewer solutes. You would need much lower pressure.0451

Well, actually, there would not be in that movement to that side.0457

But, the osmotic pressure exerted by these solutes, since they are less concentrated, is lower than the osmotic pressure on this side.0460

When we talk about osmolarity, we are really discussing solute concentration, and the unit of measurement of osmolarity is the osmole.0471

And a lot of times, we will talk about milliosmoles. We might say "oh, a solution is 500 milliosmoles per liter".0481

Therefore, when we talk about osmoregulation, we are talking about the maintenance of a constant solute concentration in the blood.0492

Solutes and fluid are obviously very closely-related, so by regulating osmolarity, the kidney is also helping to regulate fluid volume.0504

In mammals, the kidney has a major role in osmoregulation.0514

Before we get on to talking about mammals though, I want to talk about osmoregulation in some very challenging situations.0520

Animals that live in freshwater or in saltwater both face very challenging situations0526

because they are immersed in either a hyperosmolar or hypoosmolar environment.0532

So, let's talk about fish that are living in saltwater. The ocean water is hyperosmolar, their environment.0539

This fish wants to keep its body fluids at a lower osmolarity than the surrounding ocean.0557

So, it is constantly having to fight against the fact that the water is going to want to diffuse out of the fish.0567

So, you have this fish, and he is swimming around in the ocean; and the ocean has a higher solute concentration than in the fish's body.0575

Water wants to leave the fish, his body, so he is fighting dehydration.0592

If he does not fight against it, water will just leave until there is an iso-osmolarity and the solute concentration inside and outside the fish is the same.0599

In order to compensate for loss of water in a saltwater environment, the fish has some mechanisms.0612

One: they drink a lot. Now, when they are drinking, they are drinking seawater, so they are getting the water; but they are getting salt too.0620

So, he is losing water, so he is compensating by drinking water; but as he drinks water, salt is coming into his body.0630

So, what he does is he keeps the water and gets rid of the salt, and in fact, fish in saltwater environments excrete salts via their gills.0636

And this requires active transport because the salt is being moved against its concentration gradient, so this is an energy-requiring process.0647

In addition, they excrete salts via their kidneys, so the kidneys excrete salts into the urine to leave the body.0656

And they only urinate small amounts, so they get rid of the salt essentially and keep the water, so just urinate small volumes.0670

They do not lose a lot of the water via urine.0680

The opposite challenge is presented to a freshwater fish. This fish is living in a hypoosmolar environment.0687

Here is a fish, and there is not a lot of solutes out here. It is a low osmolarity environment.0700

There is more solutes inside the fish.0709

As a result, water wants to keeps rushing in and diluting out his body fluids and diluting out, then, the salt concentration.0711

What this fish needs to do is maintain his salt concentration, and he needs to get rid of excess water and hold on to salts.0721

So, this fish needs to get rid of salt. This fish needs to get rid of excess water.0729

This is accomplished by one: not drinking water. This fish is not going to drink water all the time like this one.0741

This fish is going to take salts in via his gills. In a saltwater environment, a fish excretes salt through the gills.0753

In a freshwater environment, the fish is going to take up salt through its gills, and this fish is going to urinate large amounts of dilute urine,0765

so getting rid of the water by just urinating out the excess water, holding on to the salt, getting rid of the water.0782

I do want to note that some invertebrates in, for example, saltwater environments, have a different method of adaptation.0791

Instead of fighting against the osmolarity of the saltwater and trying to get rid of all the salt,0798

some certain animals actually have a high osmolarity that is the same as seawater.0806

So, their body fluids are as concentrated as the water around them, and there is not this net loss of water to the external environment.0810

Let's start out with an overview of types of excretory systems before focusing on the human excretory system.0823

Starting out with some simpler animals and talking about a system called protonephridia, now, some flatworms just remove nitrogenous waste via diffusion.0831

The nitrogenous waste just diffuse across body surfaces. There are others, though, some types of flatworms use protonephridia.0847

Rotifers use protonephridia, and what protonephridia are, are a network of small tubes; and these small tubes lead to ducts.0858

And the nitrogenous waste are, then, excreted through the ducts, so the ducts connect to the outside of the body,0875

so, a network a tubes leading to ducts leading to the outside.0885

These ducts, though...so, let's say we have this worm - I will draw it a little bit bigger - and he has got this protonephridia.0888

And it leads to a duct to the outside where waste or nitrogenous waste are excreted.0906

Essentially he is urinating. Let's look at it that way, but it is a much simpler system, and these ducts are blind-ending.0913

So, they are open on this end. On this end, it is blind-ending, and at this thermal end, it is what is called a flame bulb.0922

If you look at the flame bulb, there are cilia that project inside in the lumen of the tubule.0935

And what happens is, then, fluid goes in, and these cilia help to move the fluid along the tubule and then, on out.0946

In this way, nitrogenous waste can leave the body, exit their tubules and then, exit out of the surface of the body via ducts.0959

Earthworms and other annelids have a different system. It is called metanephridia, and recall that earthworms have segments.0974

They also have a true coelom, and each segment in an earthworm has a pair of nephridia, so there is one pair per segment.0986

And what these consist of, what a metanephridia consist of, is a tubule surrounded by a network of capillaries, and there is also a bladder.0995

There are two openings here in this system, so here, we are going to have an earthworm, and there are actually two openings:1014

An external opening, and then, we have a system, and then, we have an internal opening.1026

So, the external opening is called the nephridiopore, and then, the internal opening is called the nephrostome.1033

Body fluid within the worm is going to enter this internal opening, the nephrostome.1054

It is going to pass into this tubule, go through the tubule and be processed and then, reach the bladder.1062

It will be urine, and then, exit the body as urine. As the fluid is going through the tubule, it is being processed.1071

And a lot of what we are going to talk about today, we talked about the human kidney is this processing.1081

By processing, I mean that at first, the fluid that goes in here might have some things that the animal does not want to lose.1086

It might need to retain salt. There might be nutrients in there, so things that we do not want to lose as waste are reabsorbed.1093

In addition, there may be waste products that are not initially in the fluid that is leaving the body.1103

So, those waste products can be secreted into the tubule to leave the body.1110

Just very simply, processing takes place in which certain substances are picked up and retained in the body.1115

Others are secreted to leave the body, and then, the urine with the waste products exits the body.1121

So, the constitution of fluid in an excretory system changes as it goes to the body.1129

Here, it is filtered. Processing takes place, and what starts out is what we call filtrate.1135

It ends up being urine.1143

Malpighian tubules are found in many arthropod excretory systems.1146

And this is a different system because these are tubules that project out from the GI tract.1162

So, if you had some insect, and he has this GI tract here, there are tubules the project out from the GI tract.1169

Food is being processed in the GI tract, and then, waste is leaving, exiting the GI tract.1187

Meanwhile, these Malpighian tubules are absorbing or picking up fluid from the body.1193

The hemolymph, which is the circulatory fluid, would be filtered, and this is processed; and then, it actually enters the GI tract.1203

The urine is going to be eliminated along with feces in this type of system because it dumps out into the GI tract.1213

Most of the water that is initially in this urine is reabsorbed along the way in the GI tract.1223

So, this is a good system for insects that live in dry environments and that need to conserve water because very little water is lost.1229

Most of what is exiting the body through the excretory system is actually nitrogenous waste.1238

We are now going to focus on the human excretory system, and a lot of this will apply to other mammals, as well, but again, this is the human system.1245

Humans have a pair of kidneys that filter the blood, and function in both osmoregulation, as I mentioned, and in the excretion of waste.1254

After the urine is formed in the kidneys, it exits via the ureters. There is a ureter leading from each kidney to the bladder.1267

Urine is stored in the bladder and then, leaves through the urethra.1279

So, this is just the basic structure, and we are going to go into a lot more detail particularly about the kidney.1288

The kidney has two sections. This outer portion here is the cortex, and this portion is the medulla.1295

The functional unit of the kidney is the nephron, so the kidney contains nephrons; and that is where the urine is made.1306

There are about 1 million nephrons per kidney, and a huge volume of blood passes through the kidneys every day.1319

In fact, one quarter of the blood that is leaving the heart goes through the kidneys.1327

Blood supply: the renal artery delivers blood to the kidneys, so we have the renal artery.1333

And then, we have the renal vein. The blood leaves the kidneys through the renal vein.1351

Before we talk about how the kidney works, you need to make sure that you understand certain terminologies.1368

The first term you need to be familiar with is filtration. Filtration is the process of the blood passing through a semipermeable membrane.1375

During filtration, certain substances will enter the kidney, those that can pass through the membrane.1397

Other substances in the blood just stay in the blood vessel and stay in the circulation.1405

Those items that pass through...so here, we have the blood vessel, which I will do in detail later about the nephron and the tubule.1411

And there is filtration right here. Those things that can pass through the capillary membrane enter the renal tubule.1424

And this liquid in solutes in this solution is the filtrate.1433

The filtrate consists of everything that passed through the membrane, that made it through the membrane into the kidney.1439

As the filtrate goes through the nephron, the filtrate enters the nephron, it enters the tubule, it is processed.1446

And processing consists of reabsorption and secretion.1456

So, it is important that you understand the difference between these two. These terms get commonly turned around and mixed up.1468

Reabsorption is the process of returning substances to the blood, so substances go from the nephron, from the tubule to the blood.1475

These are things that the body wants to keep, for example, glucose. The body uses glucose.1494

We do not want it lost in the urine. That would be reabsorbed.1500

In certain cases, some substances can be reabsorbed at certain times, secreted at others.1504

But, just keeping it simple, reabsorption are substances that we are putting back into the body, either temporarily or permanently you want to keep.1510

Secretion, that is the opposite process. Secretion is removing substances from the blood.1522

So, in reabsorption, substances are going to go back into the bloodstream.1540

In secretion, substances are going to go into the tubule to leave the body, so removing substances from the blood.1546

In other words, a substance or something that we want to get rid of. It could be excess hydrogen ions.1555

In a certain part of the kidney, it is urea. A substance goes from the blood into the tubule.1563

So, these are things we are putting into the filtrate or into the urine. Reabsorption is removing things from the filtrate or from the urine.1573

This sketch shows a nephron that has been, sort of, flattened out and stretched out.1585

In the kidney, they are actually a lot more coiled up, but to look at this for clarity, this is flattened out.1590

And remember that the kidney has two parts. It has the outer cortex, and it has an inner medulla.1596

So, if I cut the kidney in half, and I sectioned it, I am looking at this section of an opened-up kidney, and I looked at nephrons,1608

and there is a million of them here, what I would see is that these nephrons have portions.1617

If I relate their order into a certain way so that this portion - actually, I will draw that a little bit lower - all of this here is in the cortex.1624

And then, all these, this part, all these down here is in the medulla.1644

So, if I laid this, if I took this and I laid it out here, I would see this glomerulus up here in the cortex, the first part of the tubule here and then,1651

the loop reaching into the medulla and then, this latter part in the cortex, this long collecting duct going down into the medulla, so this is how it is oriented.1660

I am going to go through just an overview of what the different sections are and then,1674

what happens in each section because there is quite a lot to understand, so we are going to spend a lot of time on the nephron.1680

There are two major structures that comprise a nephron. The first is the glomerulus, and the second is this big, all this whole tubule, this renal tubule.1688

The glomerulus is a cluster of capillaries, so it is a cluster of capillaries; and it is located inside this cups-shaped structure called...1705

So, this is the glomerulus. This is Bowman’s capsule.1716

This is the section where filtration occurs, and I am going to go into that in detail after I just finish naming all the structures.1726

So, after filtration, the filtrate enters Bowman’s capsule and then, the renal tubule.1734

This first part of the renal tubule here is called the proximal convoluted tubule or just the proximal tubule.1743

This entire structure here, this loop, is called the loop of Henle.1759

And it is divided into two regions: the descending loop that goes down, and then, we have this turn; and the ascending loop.1765

So, there is a descending loop of Henle and an ascending loop of Henle, and they each have different structure and different functions.1774

As the filtrate enters the renal tubule, it is being processed. There are things being secreted into it.1782

There are things being reabsorbed. Water is moving around.1788

All this is happening throughout, and then, we get through the loop of Henle and enter the distal convoluted tubule or just the distal tubule.1793

Finally, we get to this terminal part of the nephron, which is the collecting duct.1812

And you will notice this is open at the top, and the reason is that urine from other nephrons can drain into a single collecting duct.1819

Urine from this nephron and then, there could be another nephron that drains into here.1829

When this fluid starts out, it is called filtrate. By the time it gets to the collecting duct, it is urine.1834

And then, the collecting ducts are all going to drain into the renal pelvis.1841

The urine will exit the kidney, go through the ureter, be stored in the bladder and go out the urethra.1846

This is just the big picture, and now, what we are going to do is focus first on the glomerulus and filtration.1854

Blood enters the glomerulus through this afferent arterial. It is called an afferent arterial with an A.1865

And then, the glomerulus is this network of capillaries. Blood exits the glomerulus through the efferent arterial.1882

Well, where is this blood coming from?1895

The blood enters the kidney through the renal artery, branches from the renal artery, branch off into afferent arterials.1899

These branch further into capillaries, then, form the efferent arterial, and the blood leaves the kidney.1908

Filtration is driven by the blood pressure within the glomerular vessels.1917

The fluid within these vessels is creating pressure, and that pressure is pushing this filtrate through.1923

And the blood is filtered across the glomerular membrane.1931

Certain substances can pass through the capillary membrane of the glomerulus.1937

These substances will enter this little space here called Bowman’s space and then, enter Bowman’s capsule and now be in the renal tubule as filtrate.1943

So, here is where the filtrate is created through filtration. What you should know is what substances enter the filtrate, are part of the filtrate.1957

So, what substances are small enough to get through the glomerular membrane and enter the filtrate?1968

Well, a major component of the filtrate is water. Other substances that can enter the filtrate are salts.1975

You will find sodium and chloride in the filtrate. Glucose can also enter the filtrate.1989

Amino acids are small enough to enter the filtrate, so things need to be small to get through this capillary membrane.1996

Vitamins can enter the filtrate, nitrogenous wastes such as urea.2003

Now, what cannot enter? What is too big to be filtered?2013

So, cannot enter the filtrate, cells are an example and proteins, red blood cells, white blood cells, proteins.2022

Amino acids can get in, but cells and proteins cannot; and, of course, there is plenty of fluids still left in the vessel here.2030

If somehow red blood cells and white blood cells are passing through this glomerular membrane, there is a problem with the glomerular membrane.2038

There is some kind of disease process going on, and so, in fact, if somebody has blood cells or protein or things in their urine that can be a clue,2046

there are many possibilities that different levels of the urinary tract system, but one possibility is something is going on with the glomerulus.2056

So, cells and protein should not be in the filtrate. These items are in the filtrate.2064

By the time we get to the urine, things like glucose will no longer be in there. They will have been taken back up by the body.2069

Other things will be secreted and added to the filtrate, so the composition of the filtrate changes a lot as it goes through each step until it becomes urine.2076

Urine is very different than filtrate. Filtrate reflects some of the composition of the plasma, whereas, urine is just very different.2085

Before we talk about what happens to the filtrate now that it is here entering the proximal convoluted tubule,2097

I am going to talk a bit more about the blood supply to the kidney.2105

So, blood components that have not passed into Bowman’s capsule: of course, some of the water, the red blood cells, the white blood cells, the proteins.2110

These components that have not made it into the filtrate continue out and leave the glomerulus via the efferent arterial.2122

In addition, the efferent arterial branches off to form capillaries that surround the proximal convoluted tubule and the distal convoluted tubule.2135

And there needs to be a blood supply around these tubules because items are being2146

picked up to put back into the blood or secreted from the blood into the nephron.2152

The nephron's work involves taking things from the bloodstream and putting things into the bloodstream.2161

So, there needs to be a blood supply closely associated with the renal tubule.2166

There is also a set of vessels called the vasa recta, and these are a group of capillaries, so the vasa recta.2172

These are a group of capillaries that are associated with the loop of Henle.2180

They involve one of these counter current exchange systems that we have talked about earlier on, and it actually allows the kidney to concentrate urine.2187

And I am going to talk about the loop of Henle's role in concentrating urine when we get to that part.2197

So, right now, what we left with was filtrate had been formed. It contains water and these substances, various ions.2203

And it enters the proximal convoluted tubule. The proximal convoluted tubule is a very important site for the reabsorption of products and for secretion.2214

So, I am going to clear out some space here, and we are going to talk about what is reabsorbed, what is secreted, what happens here.2226

Water and certain solutes are reabsorbed, and then, other solutes are secreted; so let's start out with reabsorption.2237

And I am going to use red. This is going to be active reabsorption, and then, I will just use blue for passive reabsorption.2247

The filtrate is here in the tubule.2263

And sodium chloride diffuses from the lumen of the tubule, from the space inside the tubule into these epithelial cells of the nephron that line the tubules.2266

So, filtrate is passing through, and there is sodium; and there is chloride, and there are these cells, and this sodium chloride is taken up by these cells.2278

From there, the epithelial cells actively transport the sodium into the interstitial fluid. Excuse me, interstitial fluid, so out here.2297

Outside of the tubule is the interstitial fluid, which plays an important role in the function of the nephron.2310

And the sodium is going to be actively transported from these cells in the tubule outside to the interstitial fluid. Chloride follows passively.2316

Now, glucose, amino acids and other substances are also actively transported outside to this interstitial fluid.2331

And then, from the interstitial fluid, these items are picked up by blood vessels.2343

So, reabsorption involves taking substances from the tubule, putting them back in the bloodstream, and that occurs via a couple steps.2349

The substances end up in the interstitial fluid, and then, they are picked up by these capillaries that are surrounding the nephron.2357

So, sodium that is actively transported, chloride follows passively.2364

There are a number of other items that are actively transported, so remember that glucose, we do not want glucose to be lost in the urine.2369

That is something our bodies could use, the same with amino acids.2379

So, these things are all reabsorbed: glucose, amino acids, vitamins. We do not want to just urinate out important vitamins.2384

Those are actively transported.2398

Now, where solutes go, water follows. Sodium is particularly important in osmolarity, and in fact, where sodium goes, water usually follows by osmosis.2403

So, as the sodium leaves, and the chloride follows through passive transport, water is also being reabsorbed.2413

In summary for reabsorption, we have sodium and chloride with water following.2426

We have glucose, amino acids and vitamins all being reabsorbed in the proximal convoluted tubule.2431

Now, let's talk about secretion, substances that are secreted, active secretion of - that is not the active color, let's change that to red - hydrogen ions.2437

Remember that the kidney plays an important role in homeostasis, and this includes the regulation of pH.2454

Secreting hydrogen ions into the tubule, those hydrogen ions will leave the body, and that will help maintain the pH of the body.2462

In fact, bicarbonate - one more thing here for reabsorption is bicarbonate - is passively reabsorbed. Hydrogen ions are secreted.2473

So, what you can see is that already the filtrate is much different than when it entered.2489

A lot of things have been picked up. Some things have been added.2493

In order to just keep the picture clear, I am going to go ahead now as we go into the loop of Henle, and let's start with a fresh picture of the nephrons.2500

So, we have done filtration in the glomerulus. Here is the proximal convoluted tubule.2508

Here is the loop of Henle.2514

The next segment that the filtrate is going to pass through is the descending loop of Henle, so descending loop of Henle right here.2518

And what is going on here is that there is additional water reabsorption. There are water channels called aquaporins, and these are water channels.2539

These are found in the descending loop of Henle, so water is being reabsorbed all along this descending loop of Henle.2554

Now, what we have here is H2O is reabsorbed. It is being put into the interstitial fluid, into the interstitium.2568

And ions and other substances are not reabsorbed.2583

The descending loop of Henle is fairly impermeable to ions and various other substances, so sodium is not reabsorbed, chloride, glucose- none of that.2588

The descending loop of Henle is permeable to water. Other substances such as ions are generally not reabsorbed here.2599

As you go deeper from cortex to medulla, there is a concentration gradient.2618

And this concentration gradient is in the interstitium. It is surrounding the renal tubule.2629

There are solutes out here, and as you go deeper from cortex to medulla, this solute concentration gets greater.2638

So, it starts out up here. There are solutes and then, greater and greater and greater and then, down here at the bottom, it is very concentrated.2647

What is driving the reabsorption of water in the kidney, or in the descending loop of Henle here in the collecting duct, as well, is this concentration gradient.2660

Without this concentration gradient, there would not be this drive for water to be reabsorbed.2673

As you go deeper and deeper into the medulla, the concentration of these solutes is greater.2684

So, even though water is leaving the tubule, and therefore, the fluid inside the tubule is becoming more concentrated,2697

water still wants to leave the tubule because the environment outside is still hyperosmolar to what is going on inside.2705

So, this filtrate is becoming more and more concentrated- a higher osmolarity.2712

However, out here is also becoming more and more concentrated, as well,2719

because of this gradient that has been generated that puts more solutes down into the medulla and fewer up by the cortex.2725

So, due to this concentration gradient, water is pulled towards the hyperosmolar environment outside the tubule.2740

Now, this situation for the ascending loop of Henle is very different than in the descending loop of Henle.2745

In the ascending loop of Henle, water is not reabsorbed. However, sodium chloride ions, are absorbed.2759

The channels here that make this permeable to water, those are not found here in the ascending loop of Henle.2773

The descending loop of Henle is permeable to water. The ascending loop of Henle is impermeable to water, permeable to sodium ions and chloride ions.2781

And in fact, the ascending loop of Henle has a very important job of maintaining. It maintains the concentration gradient from cortex to medulla.2798

Sodium chloride is transported passively. Sodium and chloride are transported passively down in the cortex, near the bottom of the loop, so the medulla.2819

So, down at the bottom of the loop of the Henle deep in the medulla, sodium and chloride are passively reabsorbed.2841

They are transported from the renal tubule to the interstitial area.2849

This movement of sodium chloride helps to maintain the concentration gradient that drives the reabsorption of water.2858

And as we go up the ascending loop of Henle in this region that is thicker...2867

It is thicker because these cells actually use more energy because the transport here of sodium is active as we go up here.2873

So, sodium and chloride are still transported, but now, we are talking about active transport of sodium as we go up the ascending loop of Henle.2883

Things to remember because I noticed a lot of information is that the descending loop of Henle, water is reabsorbed, ions are not.2895

The ascending loop of Henle maintains the concentration gradient going from cortex to medulla, and that is maintained by this reabsorption of sodium.2905

We are going to talk in a second about other ways in which this is maintained.2917

But, this sodium and chloride maintain the solute concentration out here in the interstitium.2920

Now, we get to this fluid that has made it through. We are now in the distal convoluted tubule.2926

What happens in the distal convoluted tubule? Well, some of the functions are the same as the proximal convoluted tubule.2932

Once again, we have sodium and chloride are reabsorbed. Potassium, I have not mentioned yet.2939

Potassium is, it can be reabsorbed or secreted in the proximal convoluted tubule.2952

Here in the distal convoluted tubule, potassium is actually passively secreted, and that removes excess potassium from the body.2960

Also, just like in the proximal convoluted tubule, hydrogen can be secreted.2972

One thing to note is that in the distal convoluted tubule, there is no reabsorption of glucose, amino acids, vitamins.2979

Those should have already been reabsorbed in the proximal convoluted tubule. Here, though, we have sodium chloride.2997

We have water following. We have secretion going on of things like hydrogen and potassium.3003

So, it is doing some of the same things such as a proximal convoluted tubule, but not all.3008

Finally, we get to the last segment of a nephron, which is the collecting duct.3013

Well, the permeability here, as far as water, varies, whereas, I said "oh, the descending loop of Henle is permeable to water".3019

The ascending loop of Henle is impermeable to water. The collecting duct is sometimes permeable to water.3027

And we are going to talk in a few minutes about the hormone ADH that controls3037

whether or not this collecting duct is reabsorbing water and how much it is reabsorbing.3043

But, assuming that the hormone, which is ADH, is acting on the collecting duct, then, these aquaporins are also found here in the collecting duct.3052

And if this ADH is acting on it, then, there is more aquaporins that end up in the cell membrane, and water can be reabsorbed.3064

If a person is dehydrated, then, the collecting duct can control the reabsorption of water, whereas here, it is not really a choice.3078

Here, impermeable to water, water reabsorption does not occur.3088

It occurs here. It does not occur here.3091

Here, it is a variable. It depends on the person's situation.3093

If they are dehydrated, they will absorb more water.3095

If they are fluid overloaded, then, these ducts will be closed, and they will not reabsorb water; and instead, that water will go out as part of the urine.3099

Another thing to note is that the latter part of the collecting duct is permeable to urea. Urea is reabsorbed here.3112

Now, you wonder why would urea be reabsorbed. Urea is a nitrogenous waste.3124

That is something we want to get out of our bodies. What is the point of reabsorbing that?3128

Well, there is very important reason, and that is because urea acts as another osmotically active substance,3133

as another solute essentially, to help maintain this concentration gradient.3141

I keep mentioning the concentration gradient because it is essential in concentrating the urine.3145

Without this concentration gradient, we could not produce hyperosmolar urine- urine that is more concentrated than our body fluids,3150

because this gradient is driving the reabsorption of water that I have been talking about.3157

And in addition to the sodium chloride that is reabsorbed at the ascending loop of Henle,3163

this urea reabsorbed at the collecting duct acts as a solute to help maintain this concentration gradient.3169

And actually, the urea is secreted. It is actually retaken up by the ascending loop of Henle.3177

You can think of it this way, the urea is reabsorbed. It ends up in this interstitial space here in the medulla.3189

It contributes to the osmolarity of the medulla, and then, after hanging out there a while, it is picked back up by the ascending loop of Henle.3198

And, it just makes this loop. Although, of course, some of it leaves the body in the urine.3208

The urine is going to contain hydrogen ions and ureas, potassium, other waste products, some water.3214

So, some urea will make its way out, but others, sometimes, are just recycled.3222

After going through all this, what we finally have is the urine. Remember that the urine leaves via the collecting duct.3229

It exits the kidney at the ureter, the two called the ureter, one in each kidney.3240

Those lead to the bladder, storage of urine in the bladder and then, exit from the body excreted.3245

The urine is excreted via the urethra.3254

In this next slide, I am going to focus more on the function of ADH.3257

And I am going to talk about another hormone that helps to regulate water and sodium uptake by the kidney.3262

Antidiuretic hormone is a hormone that is secreted by the posterior pituitary, which is up in the brain.3272

It is actually produced by a gland called the hypothalamus that we are going to cover in the endocrine section.3280

So, it is produced by the hypothalamus. However, it is stored in the posterior pituitary, which is right below the hypothalamus.3288

And it is secreted by the posterior pituitary. The trigger for secretion of this is an increase in osmolarity of the blood.3295

So, remember, the kidney has a very important role in the homeostasis including maintenance of the osmolarity- osmoregulation.3306

Talking a little bit about the function and the name here, it is antidiuretic hormone or ADH. You may hear this referred to also vasopressin.3316

What is a diuretic? Well, a diuretic is a substance that increases urination, increases urine output.3328

Caffeine, caffeinated drinks, coffee, caffeinated sodas, are diuretics. They increase the urine output.3338

Antidiuretic does the opposite. It decreases urine output, so it is antidiuretic.3346

It is against urine output, so it is decreasing urine output.3353

And what happens is if the body fluids become too concentrated, then, let's say for example, you had a bunch of salty chips.3359

You ate a bunch of chips. They have a lot of sodium in them, and then, you are going to have increased solutes in your bloodstream.3374

And therefore, your blood will have increased osmolarity.3383

The increased osmolarity will trigger the release of ADH by the posterior pituitary gland.3389

This is going to enter the bloodstream, so hormones. So they will enter its bloodstream, and it will act on the kidney.3399

What the kidney is going to do is kidney produces more concentrated urine, so less water will be lost in the urine- less water loss.3406

So, more concentrated urine meaning less water is lost, and therefore, if water is conserved, that will dilute out these solutes.3429

And the result will be that the osmolarity of the blood decreases.3440

And what is the mechanism by which this happens? Well, ADH acts on the collecting ducts and the distal convoluted tubule.3451

Recall that I said that the collecting ducts contain water channels- the aquaporins.3475

And what ADH does is it binds to receptors on the collecting duct.3483

And it triggers a cascade that results in an increase in the number of channels in the collecting duct.3489

The result is going to be increased water reabsorption and conservation of water, and their osmolarity will go down.3499

So, it is not triggered by just a loss of blood volume. It is specifically an increase in a concentration of the solutes in the blood:3521

increased osmolarity, release of ADH, kidney produces more concentrated urine and the osmolarity of blood will, therefore, decrease.3528

The second hormone that is very important in osmoregulation is aldosterone. Aldosterone is released by the adrenal cortex.3540

The adrenal glands, which in case you have not watched the endocrine section yet, are glands that are located right on top of the kidneys.3554

And one part of these glands is the adrenal cortex. It produces/releases aldosterone.3562

The trigger is a decrease in blood pressure or decrease in blood volume.3569

And aldosterone is one part of a system called the renin-angiotensin system, which is an important system in maintaining blood pressure.3574

So, let's just start from talking about this activation of this system.3587

There are sensors near the kidney, and they monitor blood pressure and blood volume.3592

If we have decreased blood pressure or decreased blood volume, then, this is detected by the sensors.3609

And in response, renin is released from the kidney.3619

There is a complex cascade that you do not need to know every step of or anything.3630

But, renin is part of a cascade that eventually allows for the cleavage of angiotensinogen, which is a precursor to angiotensin I.3635

Angiotensin I is converted to angiotensin II by an enzyme called ACE- angiotensin-converting enzyme.3661

Now, angiotensin II has two major effects. One is that it directly affects blood pressure.3679

It causes vasoconstriction. In other words, it causes the arteries to constrict.3687

That is going to increase the blood pressure directly.3694

So, if blood pressure is low, this system will trigger vasoconstriction - constriction of vessels - that will raise the pressure in the arteries.3698

A second effect that angiotensin II has is it triggers the adrenal cortex to release aldosterone.3708

What does aldosterone do? Well, aldosterone increases sodium reabsorption by the distal convoluted tubule.3721

Remember that where sodium goes, water will follow, so we have our nephron here, glomerulus.3739

And here in the distal convoluted tubule, if more sodium is being reabsorbed, chloride is going to follow, and water will follow.3750

This increased reabsorption of water is going to increase blood volume and blood pressure.3761

So, we are focusing on aldosterone here because we are talking about the excretory system.3775

But, this whole system helps maintain homeostasis also by angiotensin II vasoconstricting the vessels.3778

Now, one fairly common condition in westernized countries is high blood pressure/hypertension.3786

In other words, high blood pressure, which is a risk factor for stroke, for example.3797

So, in order to control high blood pressure, medications are sometimes used.3803

One of these is an ACE-inhibitor, so it is a medication that is blocking this enzyme.3806

Well, if you block this enzyme, and you block this step, angiotensin II will not exist.3814

It will not vasoconstrict, so blood vessels will remain dilated, and the pressure will be lower.3820

And aldosterone will not cause the retention of sodium in the fluid, so blood pressure will be lower.3825

There is another group of medications, and these are called ARBs, angiotensin receptor blockers, and what these do is they prevent the binding.3832

An ARB would act here, and it would prevent the binding of angiotensin II to receptors on the arteries. This is also a medication to treat hypertension.3846

So, you can see that this basic physiology actually has applications in medicine.3856

Now, we are going to review the lesson for today starting with example one: the figure below illustrates the nephron of an aquatic mammal.3863

And use the figure to explain why the loop of Henle in this mammal is shorter than the loop of Henle in terrestrial mammals.3874

The loop of Henle I showed before would be more like a human loop of Henle, so here is the aquatic animal, a shorter loop of Henle.3882

And then, the human or a typical terrestrial mammal loop of Henle would dip down farther into the medulla.3890

So, thinking about this, let's think about the environment of an aquatic animal. An aquatic mammal is exposed to water all the time.3900

So, it does not need to concentrate its urine as much as a mammal that lives on land especially a land animal that lives in a very dry environment.3915

In a desert environment, an animal will have an even longer loop of Henle, and the reason is,3923

remember that the ascending loop of Henle maintains the concentration gradient going from cortex to the medulla that allows urine to be concentrated.3928

To be more concentrated, it allows for this reabsorption of water. This concentration gradient allows for the reabsorption of water.3960

And the longer the loop of Henle is, the steeper the gradient can be. There is more distance here to pump out sodium chloride.3968

A mammal that has a lot of exposure to water may not need to concentrate its urine as much.3980

Whereas, especially an animal in a very dry environment like the desert, it is going to have to really minimize water loss and have a longer loop of Henle.3986

Example two: why do animals that live in a dry environment secrete, or actually it is excrete, nitrogenous waste in the form of uric acid?3998

Well, remember that there is a couple reasons.4010

In general, uric acid is less toxic than ammonia, so that is why it would be uric acid versus ammonia, but why not urea?4015

Well, dry environment is the key here.4022

Remember that uric acid is not water-soluble, and the big challenge in a dry environment is going to be water conservation.4024

Therefore, uric acid is excreted as a paste. It is not excreted in solution in urine.4035

By excreting it as a paste, the result is minimized water loss. Get rid of the nitrogenous waste with very little water loss.4050

Through what mechanisms do fish living in saltwater maintain their osmolarity below that of surrounding water.4064

Remember that a fish in saltwater is in a hyperosmolar environment. The challenge is going to be not getting dehydrated.4070

Water is trying to leave. Salt is trying to enter, so what this fish needs to do is conserve water, get rid of salt.4086

They do that a few ways. They drink a lot water.4097

Of course, this is seawater, so they are getting the water they need; but they are getting all the salt too, so they get rid of the salt.4101

They excrete salt via their gills, and this is through active transport. They also excrete salt via their kidneys, and they urinate only small amounts.4109

So, ways to prevent dehydration, ways to hold on to water and get rid of salt: drink a lot of water, and you are taking in a lot of salt, too,4131

so get rid of the salt by the gills, get rid of the salt via the kidneys, and kidneys reabsorb most of the water.4141

There is very little urine, and it is very concentrated.4150

Example three: on the figure below, indicate the following: 1. the section of the tubule that maintains the concentration gradient from cortex to medulla.4155

Here, we have the glomerulus, the proximal convoluted tubule. Now, here is the loop of Henle.4166

Remember that the loop of Henle maintains the concentration gradient, and particularly, it is the ascending loop of Henle. Therefore, no. 1 is this section.4172

It maintains this concentration gradient that allows for the reabsorption of water and the production of a hyperosmolar urine.4190

Two: the structure responsible for the reabsorption of glucose.4199

So, initially, blood is filtered by the glomerulus, and filtrate enters the proximal convoluted tubule.4203

In the proximal convoluted tubule, there are some things like glucose and amino acids and vitamins that we do not want to lose in the urine.4213

So, those are reabsorbed right here at this first section of the nephron.4223

The proximal convoluted tubule right here, no. 2, is the structure where reabsorption of glucose occurs.4229

Example four: a child contracts a gastrointestinal infection that causes severe diarrhea. As a result of this fluid loss, his blood pressure drops.4242

So, vomiting, bleeding, diarrhea, these can all cause fluid loss, and fluid loss, in turn, can cause a drop in blood pressure.4254

What hormone will be released to help maintain his blood pressure? By what mechanism will increase the child's blood pressure?4265

Well, remember those two hormones we talked about.4273

And the one that is triggered by a drop in blood pressure or blood volume, actually, is aldosterone.4275

Aldosterone is released by the adrenal glands in response to a drop in blood pressure or blood volume.4282

What is the mechanism of action? Well, aldosterone, remember, acts on the distal convoluted tubule.4291

And what it does is it increases the reabsorption of sodium, and water follows by osmosis.4301

So, more sodium is removed from the tubule back into the blood, and where a solute goes, water will follow.4317

That concludes this section of Educator.com on the excretory system.4327

Thank you for visiting.4332

Welcome to Educator.com.0000

In this section of animal physiology, we will be focusing on the endocrine system.0002

Hormones are molecules that are released by endocrine glands, and they travel via the blood stream to illicit a response from distant target tissues.0010

To understand endocrine glands, we use an example, and an example would be the thyroid gland.0023

The thyroid, which we will talk about in more detail later, secretes thyroxin or thyroid hormone into the blood stream.0028

And thyroxin goes on to affect target tissues and organs.0039

And the effect that it has on a tissue or organ maybe different depending on what type of tissue it is, so the results are overall an increase in metabolism.0050

And that results in an increase in temperature, heart rate and changes in other physiological processes.0062

So, one hormone can have multiple effects in the body.0071

Endocrine glands secrete substances, secrete hormones, into the extracellular fluid.0076

From the extracellular fluid, the hormone diffuses into the blood stream.0084

So, here, I am talking about thyroxin being secreted into the blood stream, but to get a little more subtle about it,0090

what happens is that the hormone is secreted by the thyroid cells into the fluid surrounding the cells0095

and then, from there, can diffuse into the blood stream and then, be delivered throughout the body.0102

Although, the hormone will go throughout the body via the blood stream,0108

it is only going to affect target tissues that have a receptor for that particular hormone.0111

Exocrine organs or exocrine glands secrete substances via ducts. They secrete them via ducts- secrete substances into ducts.0119

So, it is exocrine, whereas, endocrine glands secrete substances into the blood stream.0133

Recall that we talked about the pancreas when we covered the GI tract, when we covered the digestive system.0145

And I said that the pancreas is both an exocrine organ and an endocrine organ.0151

So, to give you another example of an exocrine gland- sweat glands, salivary glands. They secrete substances into ducts.0157

Now, the pancreas, as we will talk about shortly, is both an exocrine gland and an endocrine gland.0164

And its exocrine function is that it secretes digestive enzymes via the pancreatic duct into the small intestine such as lipases and amylase.0181

However, it also secretes - so this is digestive enzymes via ducts - hormones -0192

we will talk specifically about these hormones, insulin and glucagon - into the blood stream.0203

So, the pancreas is actually both an exocrine gland and an endocrine gland.0208

Hormones have many different effects. Growth hormone regulates growth, as the name suggests.0213

Estrogen and testosterone affect development and reproduction. They stimulate the formation of gametes.0221

Other hormones like insulin and glucagon regulate blood glucose level. Calcium levels, metabolism as I mentioned, these are all regulated by hormones.0228

Before we go on and talk in detail about hormones and the endocrine system, I want to mention a couple of other terms you should be familiar with.0239

Endocrine system is one way of signaling. The nervous system is another method that the body has for signaling and coordinating activity.0248

A third mechanism is what is called paracrine signaling, and in paracrine signaling, a substance is released by an organ; but it affects only nearby cells.0257

So, this is local regulation, so a substance secreted and affects nearby cells. It diffuses over and affects only cells nearby.0269

This is endocrine signaling where the substance is released, but it diffuses into the blood stream and can go all over the body. That is endocrine.0286

Whereas, in paracrine, I have an organ with cells, and it is secreting substances; and these substances only affect other cells that are nearby.0296

They are not going to go out into the blood stream and go all over the body.0308

Finally, pheromones also are involved in signaling, and these are a means of communication, but often, it is to signal members of the same species.0314

For example, pheromones may be used to mark territory for an animal or to attract a mate.0334

So, these are method of communication that is not just within the body.0342

But, it can also signal another member of the species that it is that individual's territory, or that individual is available for mating, to attract a mate.0348

So, this is another type of signaling.0359

OK, now, I am going to review mechanisms of hormone action, and we talked about this in detail in the lecture on intercellular communication.0365

If you have not already watched that, I suggest that you watch that.0378

However, I am going to review the major points so that you can understand endocrine action.0382

In this lecture though, we are going to focus more on specific endocrine organs, the hormones they secrete and the effects of those hormones.0386

But just looking at the molecular mechanism of hormone action, as I said,0395

cells can communicate with each other through both electrical signals as with the nervous system and through chemical systems.0400

And hormones are a chemical signal, so substances released from one cell such as a cell in the thyroid gland.0408

Thyroxin is released, travel and go through a several step pathway to illicit a response in the target cell.0417

Now, there is two major mechanisms of action. I am going to talk about the first one here where it is a more complex pathway.0426

And this pathway, there are several steps. The first one is the reception of the signal.0435

The second is the transduction of the signal, and the third is the response phase.0447

Recall that in the first step, the ligand, which is a molecule that binds to a target cell, reaches the target cell, binds to the receptor.0456

So, that is the reception phase, and right now, I am just looking at extracellular receptors, receptors that in the cell membrane.0473

But, we will talk about intracellular receptor soon, so this first phase is binding.0481

This binding often causes a...so, it binds, and the result is a conformational change in the receptor that may activate another molecule.0486

So, there might be a conformational change in this receptor that causes it to be able to bind this molecule.0497

This molecule may in turn activate via an enzyme that activates another molecule that, then, cleaves another molecule and on down.0504

And what this second phase is, is cascade of one molecule activating another molecule is transduction.0511

Recall, we talked about signal transduction pathways.0518

And during these pathways, the message is passed from the exterior of the cell to the interior and at the same time, the signal is amplified.0522

And signal transduction pathways often involve, so this step two often involves second messengers such as cyclic AMP or IP3 or diacylglycerol.0533

So, first phase, the signal is received.0552

The second phase, the signal is transduced or sent from the place where it has been received to the interior of the cell.0555

Finally, that message is passed all the way to the interior.0564

And here, we have the nucleus, and what this message may do is result in increasing the level of transcription of a gene.0568

It may decrease the level of transcription of a gene, or it may act on the protein level, so gene or protein level.0577

So, the response maybe to activate an existing protein or inactivate it.0587

Now, this is the situation for the extracellular receptor. However, some hormones can cross the cell membrane.0595

There are several major classes of hormones. Two, in particular, that we will focus on, the first two, the first one are steroid hormones.0606

Now, steroid hormones are derived from cholesterol. Therefore, they are fat soluble.0618

They can cross the cell membrane. An example is the hormone cortisol.0624

The second class of hormones are the peptide hormones.0631

The peptide hormones are generally insoluble to the cell membrane, so cannot cross the cell membrane. An example is insulin.0635

There is a third class of hormones that are amine hormones derived from the amino acid tyrosine, and sometimes these are fat soluble.0653

Some can cross the cell membrane. Others cannot, so it depends on this one.0662

A peptide hormone is going to have to bind to an extracellular receptor and use signal transduction to get its message into the interior of the cell.0670

Now, the situation is different for a steroid hormone.0679

For a steroid hormone, the receptor might actually be here inside the cell, and then, this steroid hormone can enter the cell,0682

bind to the receptor, travel to the nucleus and act directly as an initiator of transcription or to shut off transcription, sometimes, even permanently.0693

It does not need to use this mediator of a signal cascade. In fact, some steroid hormones even have receptors that are in the nucleus.0707

So, what will happen is, the hormone will travel in, bind, and it is already ready to go to activate or turn off transcription.0718

These are two mechanisms of hormone action.0731

Another topic involving mechanism of hormone actions is the idea of negative feedback inhibition.0739

We have touched upon negative feedback a few times in the course.0749

But, just to remind you how this would work and put it in the context of hormones, is that the production of a hormone will cause a response.0753

That response in negative feedback or some aspect of that response will turn around and0764

decrease the production of the hormone so that you will not end up with too much hormone.0772

You will not end up with too little. It is a loop of regulation.0779

Let me explain this, giving in an example of testosterone. Testosterone is produced by the testis, and the signals starts up here in the hypothalamus.0783

And the hypothalamus we will talk about regulates the anterior pituitary.0799

In this case, it releases a hormone called gonadotropin-releasing hormone that acts on the anterior pituitary.0804

You do not need to remember all these details right now just talking about negative feedback.0814

The anterior pituitary, then, releases luteinizing hormone, which acts on the testes, and the testes in response produce testosterone.0818

Testosterone exerts a variety of effects that we will talk about, so it exerts its effects on target organs.0833

However, it also suppresses further production of testosterone. It suppresses the hypothalamus from initiating this flow of testosterone production.0842

So, it inhibits the hypothalamus from releasing the GnRH, which will in turn cause the anterior pituitary to not release LH and on down.0861

The feedback is "alright, there is testosterone produced, turn around and stop production of more testosterone".0873

Otherwise, there would just be more and more testosterone, and there would not be anything regulating it.0883

The hypothalamus releases GnRH, and one of the results of that is testosterone. That is a response.0890

And that response goes and shuts off the initial signal.0897

We are going to now go on and talk about specific endocrine organs, and we are going to start with the pancreas, which I already mentioned briefly.0907

As I said, the pancreas is both an exocrine gland.0917

This is its function in digestion. It produces and secretes digestive enzymes via a duct and an endocrine organ.0920

In its endocrine function, the pancreas secretes two hormones.0929

And these hormones are actually produced by special groups of cells called islets of Langerhans, and there are two types.0934

There are beta cells, and the beta cells produce insulin, and the alpha cells produce glucagon.0943

These two hormones have opposing actions. They are what is called antagonistic hormones.0952

Beginning with insulin, let's say that blood glucose is high. You eat a bunch of sugary foods, and it is broken down; and blood glucose is high.0961

What this is going to do is it is going to trigger the pancreas to release insulin.0978

The effect of insulin is to bind to target cells and cause them to take up glucose, so it stimulates cells to take up glucose.0992

If the cells take the glucose up, it takes it out of the blood stream, and the result will be blood glucose is decreased.1004

So, we started out with high blood glucose. The result, the final effect of insulin is to decrease blood glucose levels.1018

And just to note that various cells can take up glucose, but in the liver, excess glucose, remember, is stored as glycogen.1026

So, that is another function of the liver. In the liver and some other cells, as well, the glucose is stored as glycogen.1034

Now, glucagon has the opposite effect. Let's say that you do not eat for a while.1050

You are getting pretty hungry. Your blood sugar gets low.1056

Now, you have blood glucose is low. That is going to stimulate the pancreas to release glucagon.1059

Glucagon tells the liver to break down the glycogen, so it stimulates the liver to break down glycogen, and the result is going to be a release of glucose.1077

The glycogen is broken down into glucose. Therefore, blood glucose is increased.1096

The effect of glucagon is to increase blood glucose. The effect of insulin is to decrease blood glucose.1104

You have probably heard of diabetes. Diabetes mellitus is a disorder in which there is either a deficiency of insulin or insulin is being produced.1114

So, there is enough insulin, but the cells are unresponsive to insulin.1127

The result of either form of diabetes is that blood glucose levels end up being too high.1131

And over time, a persistently high blood glucose level can cause damage to various organs to the kidneys, to the eyes, and to the cardiovascular system.1138

This is treated either by giving an individual insulin if they do not produce insulin or medications that allow them1147

to utilize the insulin more effectively if they are producing it, but their body is not responding to the insulin.1156

The second organ we are going to cover is the anterior pituitary, which produces many hormones.1166

The pituitary gland is located in the brain below the hypothalamus.1173

The hypothalamus regulates the anterior pituitary, and there are two parts of the pituitary: the anterior pituitary and the posterior pituitary.1179

And they have very different functions, so we are going to focus on these separately.1193

First, the anterior pituitary, and as I said, it secretes multiple hormones. Some of these hormones are what is called tropic hormones.1197

Tropic hormones act on other endocrine glands.1207

So, instead of just acting directly on a tissue like say thyroxin goes and acts on a tissues,1211

what a tropic hormone does is it acts on another endocrine organ, and then, it might stimulate the release of a hormone from that organ.1217

So, we will start out with some of the tropic hormones that are produced by the anterior pituitary for example thyroid-stimulating hormone.1225

And these are often known by their initials, so TSH. This is just often called TSH.1237

This is released from the anterior pituitary at a signal from the hypothalamus.1243

And it travels to the thyroid and stimulates the release of thyroid hormone, so stimulates the thyroid gland.1250

So, it is not having a direct effect on the physiology of the body.1262

What it is doing is stimulating another endocrine organ that will release a hormone that has physiological effects.1267

The second hormone that I am going to discuss is adrenocorticotropic hormone, and right here in the name, it tells you it is a tropic hormone.1277

ACTH stimulates the adrenal cortex, and as we are going to discuss, the adrenal gland even though it is one organ, it is almost like two glands in one.1291

The adrenal cortex and the adrenal medulla have different function, so it stimulates the adrenal cortex.1303

And the adrenal cortex in turn releases mineralocorticoids like aldosterone and glucocorticoids like cortisol.1314

The anterior pituitary also secretes hormones that are important for reproduction for example follicle-stimulating hormone, usually known as FSH.1324

It stimulates the production of gametes, so ova in females, sperm in males.1348

Luteinizing hormone, LH: this causes the rupture of the follicle in the ovary so that the ovum is released during ovulation.1366

I will just put "release of ovum", and it also stimulates the production of testosterone in males.1389

And we are actually going to talk in more detail about FSH, LH and testosterone, progesterone, estrogen in detail in a separate lecture on reproduction.1400

But for right now, you just need to know that these are released by the anterior pituitary and affect reproduction.1417

Additional hormones produced by the anterior pituitary are growth hormones, so growth hormone is not a tropic hormone. It has a direct action.1426

It stimulates the growth of bones and muscles.1440

A disorder called gigantism where people grow extremely tall can be a result of too much growth hormone.1447

There is a form of dwarfism that results from too little growth hormone and can sometimes be treated with growth hormone.1456

Prolactin: the name tells you lactin like milk, and it stimulates the development of the mammary glands1465

and also, the production of milk by the mammary glands, so stimulates development of mammary glands and milk production.1475

The last hormone we are going to talk about with the anterior pituitary is melanocyte-stimulating hormone.1497

In humans, this hormone stimulates the production of melanin, which is a pigment that is responsible for skin color, eye color, so pigment.1514

It is a pigment, so it stimulates melanin production.1525

And I do want to note that different hormones can elicit a different response in a different species.1530

So, in a human, melanocyte-stimulating hormone might have one function, and it elicits a slightly different response in another species.1537

Next, we are going to talk about the hypothalamus and the posterior pituitary glands.1548

As I mentioned, the hypothalamus regulates the anterior pituitary.1555

So, it secretes a bunch of hormones that act on the anterior pituitary, and it also secretes a couple of hormones with direct actions.1562

First, talking about regulation of the anterior pituitary, what happens is the hypothalamus releases hormones that are either stimulating or inhibiting.1570

They either stimulate or inhibit the anterior pituitary to release its hormones.1589

And this occurs by the release of the hormone from the hypothalamus into a group of capillaries.1595

So, it releases the hormone into a group of capillaries, so hypothalamus that surround it. There is a capillary network surrounding it.1603

Then, the hormones travel via the capillaries to the portal veins. It is called the portal veins.1615

And these portal veins connect to a second network of capillaries, and these capillaries surround the anterior pituitary.1621

And in that way, the hypothalamus can regulate the anterior pituitary.1632

Just to give you some examples of these hormones, one is thyrotropin-releasing hormone- TRH.1637

Another hormone that I already mentioned is...1653

So, this will act on the anterior pituitary and stimulate thyroid-stimulating hormone1657

to be released from the anterior pituitary, which will go on to stimulate the thyroid.1664

Gonadotropin-releasing hormone: GnRH stimulates the release of luteinizing hormone and follicle-stimulating hormone by the anterior pituitary.1670

There are many others. There are growth-hormone, releasing hormone, and it indicates that it stimulates the anterior pituitary to release growth hormone.1692

There is corticotropin-releasing hormone. It stimulates the release of ACTH by the anterior pituitary.1706

This is the function of the hypothalamus to regulate the anterior pituitary.1724

It is located in the brain near the pituitary, and what the hypothalamus does is it secretes...1735

The hypothalamus and the pituitary are right about in this region where the purple is.1743

So, the second function of the hypothalamus is to produce two hormones that are stored in the posterior pituitary.1748

It regulates the anterior pituitary, one function, and second function is to produce oxytocin and antidiuretic hormone.1755

These are stored in the posterior pituitary, and then, at a particular signal, they will be released or secreted by the posterior pituitary.1774

The function of oxytocin is to stimulate uterine contractions, so during child birth, the uterus will contract to cause the baby to be delivered.1791

So, it stimulates uterine contractions.1804

A second hormone, ADH, antidiuretic hormone is discussed in detail in the lecture on the excretory system.1814

But, recall briefly that what ADH does is it cause increased reabsorption of water by the kidney.1821

So, If there is an increase in osmolarity, the blood becomes more concentrated in terms of solutes that signals that the body needs to conserve water.1840

It needs to hold on to water, and that will trigger the release of ADH by the posterior pituitary,1850

which the ADH will, then, act on the kidney to cause the reabsorption of water.1858

The result is that more water will stay in the blood stream to dilute out the blood.1864

And the urine will become more concentrated thus, decreasing the loss of water into the urine.1869

OK, this was the hypothalamus and the posterior pituitary. The next set of glands we are going to talk about are the adrenal glands.1876

And the adrenal glands are located right on top of the kidneys, so on top of the kidneys, that is where they are located.1884

And the two parts of the adrenal glands, the adrenal cortex and the adrenal medulla,1895

even though they are together, they are functionally really separate endocrine glands.1902

They have separate cell types and separate hormones that they release.1905

So, these two sections are the adrenal cortex and the adrenal medulla.1911

So, the adrenal cortex, what happens is the anterior pituitary secretes adrenocorticotropic hormone, ACTH.1916

ACTH, then, acts on the adrenal cortex, and the adrenal cortex releases mineralocorticoids and glucocorticoids.1930

Mineralocorticoids are involved in maintaining sodium and water balance in the body. An example of a mineralocorticoid is aldosterone.1950

Recall that aldosterone, again, we talked about this in the lecture on the excretory system and the kidney,1964

but that aldosterone increases sodium - let's just talk about aldosterone for a minute - reabsorption in the kidney.1971

And when more sodium is reabsorbed, water will follow. So, this in turn triggers increased water reabsorption.1986

So, If an individual has low blood pressure or decreased volume, their body needs to hold on to more water.1996

So, low blood pressure, low volume, would stimulate the production and secretion of aldosterone,2005

which would signal the kidney to hold on to water to thereby, increase blood volume and blood pressure.2015

So, those are mineralocorticoids.2023

The second type of hormone produced by the adrenal cortex are the glucocorticoids.2025

An example is cortisol and the gluco right here, tells you that these are also involved in glucose regulation.2036

So, glucose levels are increased by glucocorticoids like cortisol.2047

They also have various other functions such as suppressing the immune system and the inflammatory response.2053

The second area of the adrenal glands is the adrenal medulla.2062

The adrenal medulla releases epinephrine, which is also known as adrenaline and norepinephrine or also known as noradrenaline.2070

These are responsible for the fight or flight response.2091

If a person or an animal is...there is a threat, somebody is chasing you, your body will release epinephrine and norepinephrine.2099

And what that is going to do is give you what you need to either fight the threat or run away from it.2111

And what you are going to need to do that? What you are going to need more oxygen, more sugar, more energy.2116

So, what is going to happen is an increase in heart rate, increase in blood pressure. Bronchodilation open up the airways, get more oxygen in.2124

Blood will be shunted to the skeletal muscles so that you can run or fight. Glucose levels will increase.2138

The pupils will dilate, so that is the fight or flight response.2147

Next, we are going to discuss the thyroid gland, which I mentioned as an example early in the lecture.2156

The thyroid gland is located in the neck, and it produces thyroxine and calcitonin.2162

So, recall that the anterior pituitary releases thyroid-stimulating hormone, which acts on the thyroid to promote the release of thyroxine.2170

Now, I am going to talk a little bit about some terminology that you will see.2185

We are focusing on thyroxine, but there is another hormone released by the thyroid gland.2187

The other name for thyroxine is T4, and the reason it is called T4 is there are 4 iodine atoms in it.2192

There is a second hormone produced by the thyroid gland called T3. As you can imagine, it has three iodine atoms.2201

Mostly, what the thyroid produces is T4, thyroxine, but in its target cells, that T4 is usually converted to T3.2211

For simplicity, I am just going to talk about thyroxine, T4, but this converts to T3; and then, that has an action on target cells.2219

The action of thyroxine ends up being to increase the metabolism.2231

Because iodine is required to make thyroid hormones, T3 and T4, a lack of iodine results in a condition called a goiter.2241

If there is iodine deficiency, lack of iodine, the result can be goiter, and in goiter, the individual with the condition will have a very enlarged thyroid gland.2251

In the U.S. for example, iodine is added to salt to help prevent iodine deficiency.2264

To understand the effects of thyroid hormone, let's look at the extreme cases.2273

Let's say somebody has too much thyroid hormone, and the result is a condition called hyper - so high thyroid - hyperthyroidism.2277

Their metabolism is going to be really increased, and the symptoms that they will get are they are going to be very hot.2292

They are going to lose weight. They might feel anxious.2304

Their heart is going faster. They might even have palpitations, problems sleeping2308

They are really hyped up, and thyroid increases the metabolism; but if that goes too far, too much, then, we can have some negative symptoms result.2313

Graves' disease is a cause of hyperthyroidism. It is actually an autoimmune disease.2324

What happens is there is an antibody that mimics TSH. Remember that TSH stimulates the thyroid to produce thyroxine.2332

Now, normally, the pituitary will not release TSH unless there is a stimulus like a person's cold.2348

And their body says "OK, we need to increase the metabolism here".2354

But this antibody is not under the normal controls of the body like TSH release would be.2359

It is an imposter but it is still can act on the thyroid and cause it to release thyroxine the way normal TSH would.2364

As a result, the person's metabolism is increased.2373

The other possibility is hypothyroidism, and in this case, we have decreased levels of thyroid hormone.2379

There is also an autoimmune disease that can cause this.2394

It has different mechanism in the opposite situation with Graves' where the thyroxine is not being produced in high enough levels.2397

These individuals, instead of losing weight, they will gain weight. They will feel cold.2406

They might have hair loss, lethargic. They will sleep too much.2413

They might become depressed. So, everything is decreased instead of increased like with hyperthyroidism.2420

The second hormone that you should be familiar with regarding the thyroid gland is calcitonin, and calcitonin decreases blood calcium level.2430

It does this by stimulating, so it stimulates the uptake of calcium by the bones.2448

So, the bones are reservoir to store calcium. Therefore, if blood calcium levels are high - so this is in the blood - then, calcitonin is released,2461

uptake of calcium by the bones, also, calcitonin stimulates the loss of calcium via the kidney and loss of calcium via the kidney, so it is excreted out.2477

Then, the result is blood calcium levels will be decreased, so it helps to maintain homeostasis in that way.2492

There is a set of four glands located right behind the thyroid gland in the neck, and these are the parathyroid glands.2505

The hormone they secrete is called parathyroid hormone or PTH.2513

PTH has the opposite effect of calcitonin, so we have the parathyroids. They release PTH, and PTH is going to increase calcium levels in the blood.2520

How does it do that? Well, what PTH actually does is stimulates the breakdown of bone to release calcium.2541

A second action is to stimulate the reabsorption of calcium in the kidney.2561

Calcitonin was causing calcium to be stored in the bone and was causing calcium to be lost by the kidneys,2577

so getting rid of calcium or storing it to decrease blood calcium levels.2591

Here is the opposite: increasing blood calcium levels by breaking down bone and having the kidney hold on to or reabsorb calcium.2597

It is a physiological antagonist, PTHs to calcitonin.2606

The last set of endocrine glands that we are going to talk about are the ovaries and the testis.2613

And these release the sex hormones: estrogen, progesterone and testosterone.2617

Now, we are going to again talk about this in more detail under the separate set of lectures on reproduction.2622

But, for completeness to just introduce this topic as part of the endocrine system, starting with the ovaries,2630

the ovaries produce estrogen and progesterone.2638

As it says right here, estrogen is responsible for the development of the secondary sex2647

characteristics in females during puberty and maintains those characteristics later on.2654

Secondary sex characteristics are not directly involved in reproduction, so it is not the actual production of sperm or egg.2659

But, secondary sex characteristics have to do with attracting a mate or their characteristics that are different in males and females.2670

So, that is part of estrogen's job is to cause the development of secondary sex characteristics during puberty2677

in females such as stimulating breast development also, a change in shape of the pelvis in females.2685

Estrogen plays a role on the menstrual cycle.2693

Progesterone, I just remember pro-gestation because it is a hormone that maintains pregnancy. It prevents the uterine lining from shedding.2697

It promotes an environment that will allow for the embryo and fetus to survive.2705

The testis secrete testosterone.2712

Testosterone stimulates the development of secondary sex characteristics in males such as facial hair, deepening of the voice and increase muscle mass.2715

And again, we are going to talk about more functions and how the progesterone, estrogen, testosterone work in this section on reproduction.2726

Now, though, we are going to go on and do some review on the endocrine system.2738

Example one: Match the following hormones with their descriptions.2742

Parathyroid hormone is the first one, and let's look at the choices:2748

Parathyroid hormone increases the metabolic rate, increases calcium level in the blood, stimulates the fight or flight response, stimulates uterine contraction.2753

Remember parathyroid gland is located near the thyroid in the neck, and PTH or parathyroid hormone causes an increase in calcium level.2766

It causes bone to breakdown and release calcium into the blood, so the answer here is B.2778

Two: oxytocin. We have choice of increase the metabolic rate, stimulate the fight or flight response or stimulate uterine contractions.2785

And in fact, oxytocin, which is produced by the hypothalamus and stored in2795

the posterior pituitary does stimulate uterine contractions allowing for child birth.2800

Thyroxine: as we talked about, thyroxine increases the metabolic rate, which leaves us with epinephrine and norepinephrine,2807

which are secreted by the adrenal medulla and stimulate the fight or flight response.2817

Example two: why is the pancreas considered to be both an endocrine organ and an exocrine organ?2827

Well, let's start with exocrine. Remember that an exocrine organ secretes substances via ducts.2834

In its function as part of the digestive system, the pancreas secretes digestive enzymes such as lipases and amylases through the pancreatic duct.2847

Therefore, it is an exocrine organ.2868

In its role as an endocrine organ, the pancreas also secretes hormones directly into the blood stream.2879

And these hormones involve the regulation of glucose. In the islets of Langerhans are produced insulin and glucagon.2892

Therefore, the pancreas is both an exocrine gland and an endocrine gland.2904

Example three: describe how the opposing actions of insulin and glucagon regulate the level of glucose in the blood.2910

Remember that these are antagonistic hormones. They cause opposite responses in the body.2918

Let's start out with when the blood glucose is high, so blood glucose increases.2929

If it is too high, the pancreas will release insulin. Insulin will cause uptake of glucose by cells, so it takes that glucose out of circulation.2937

The result by picking up the glucose and some of it is stored in the liver as glycogen2955

is going to be that the blood glucose level drops, so decreased blood glucose.2962

Let's say that the blood glucose level becomes too low, so low blood glucose. The result is going to be that the pancreas will release glucagon.2970

Glucagon is going to stimulate the breakdown or the hydrolysis of glycogen in the liver.2988

Glucose will be released into the blood stream. Therefore, blood glucose will go up.2999

So, between the two, glucose can be very tightly regulated.3008

Glucose gets a little too high, insulin is released. Glucose gets a little too low, glucagon is released.3012

Example four: symptoms of Cushing's syndrome include weight gain, thinning of the skin and easy bruising.3026

The cause is an increased level of cortisol in the blood.3034

Over secretion of hormones from which gland could result in Cushing's syndrome?3038

Well, recall that cortisol and other corticosteroids are released by the adrenal cortex.3042

Therefore, if an individual had over-secretion of hormones by the adrenal cortex,3051

they would have increased cortisol level and could exhibit these symptoms.3060

That concludes this discussion on the endocrine system here at Educator.com.3066

Thank you for visiting.3071

Welcome to Educator.com.0000

In this section of animal physiology, we will be focusing on the nervous system.0002

And the nervous system provides a mechanism for the body to receive and send information.0007

And this can be external stimuli that is being received such as sounds and smells or internal information such as temperature,0013

blood pressure that allows the body to coordinate functions and maintain homeostasis.0022

We are going to start out by talking about different types of nervous systems and then, focus in detail on the human nervous system.0031

The simplest nervous system is called a nerve net.0038

And you will recall in the section in diversity of life, I described a nerve net as being found in cnidarians like jellies and Hydra.0042

So, a nerve net is simply a diffused group of interconnected nerve cells. There is no central nervous system.0056

If you look at a simple animal but with a more advanced nervous system than the nerve net, that would be the nervous system of a flatworm.0067

So, the flatworm has longitudinal nerve cords and a pair of ganglia, so nerve cords and ganglia.0079

Recall that ganglia are clusters of nerves, and in the flatworm, these are at the anterior end of the organism.0096

And they allow for processing of sensory input.0109

This gets us to a related point in the evolution and development of the nervous system and that is the concept of cephalization.0113

Recall that in bilaterally symmetrical animals, cephalization developed.0122

And this is the development of a head end in which sensory organisms are clustered or concentrated.0129

Sensory organs are concentrated here and ganglia to process this information, then eventually, in more advanced animals a brain.0141

To give you just examples of an overview of nervous systems and a couple other groups of0155

animals before we go on to talking about vertebrates and particularly humans- arthropods.0160

Arthropods have well-developed sensory organs.0168

They have eyes. They have organs that allow for smell, antennas for touch and even ears in some species.0178

Some have ganglia. Other arthropods actually have brains.0186

Echinoderms such as sea stars have a less well-developed nervous system. They have, recall, a nerve ring with cords that radiate out into their arms.0193

Next, we are going to go ahead and focus in on the vertebrate nervous system.0215

I am going to start with an overview of the organization, discuss the neuron and transmission of nerve impulses and then, revisit the central nervous system0222

in more detail once we have covered the terminology that you need to understand the structure and function of the central nervous system.0233

Here is the nervous system overall, and there are two major divisions.0241

The central nervous system consists of the brain and spinal cord, and the peripheral nervous system is everything else.0245

The PNS can be further divided into two major systems: the autonomic nervous system and the somatic nervous system.0255

The somatic nervous system is responsible for voluntary activities, so voluntary activities such as when you walk or talk or turn your head.0265

Those are all under the control of the somatic nervous system.0279

By contrast, the autonomic nervous system is responsible for involuntary activities.0284

The heart, the GI tract and the endocrine organs are all regulated by the autonomic nervous system.0291

Some systems actually split off into a third division, which is the enteric nervous system, and this is regulation of the GI tract.0297

Instead, they are just putting it under the autonomic system, so you may encounter that.0308

So, nervous system: central versus peripheral.0314

Peripheral is divided into autonomic and somatic, and then, autonomic has two further divisions: the sympathetic nervous system and the parasympathetic.0317

The sympathetic nervous system is responsible for the fight or flight response.0329

Recall that the fight or flight response results in an increase in heart rate, respiratory rate, glucose. Blood is shunted to the skeletal muscles.0335

So, the idea is that if there is a threat like a person is chasing you or something is about to fall on you and you have to run away really quickly,0350

your body triggers this giving you the oxygen, the glucose, the energy, everything you need to either fight or run away.0360

The opposite is parasympathetic. This is often described as rest and digest.0373

With the fight or flight, we see an increase in the heart rate, increase blood pressure, increase in respiration. Blood is shunted to the skeletal muscles.0381

With the rest and digest, things return to calmer. There is a decrease in the heart rate, decrease in the respiratory rate. Blood is shunted to the GI tract.0395

Now we have an overview, we are going to focus on the functional unit of the nervous system,0418

which is the neuron, beginning with the structure of the neuron.0424

And then, we will talk about the way that signals are transmitted along the neuron and from one neuron to another neuron or cell.0427

Beginning with the cell body, the cell body contains the nucleus and organelles for the nerve cell.0437

Extending from the cell body are projections called dendrites.0448

Dendrites receive incoming stimuli, and there are various types of stimuli.0454

It depends on the type of neuron. In the eye, the dendrites are specialized to receive could be light.0467

A stimulus on your skin, there are pain receptors, different touch receptors.0476

The stimulus that is received, it can be specialized.0482

Or the stimulus might just be another neuron that is synapsing on this neuron and stimulating this neuron to transmit the signal.0486

So, it could be an outside stimuli or another cell synapsing on this one.0496

This section right here, leading away from the cell body, is called an axon hillock.0501

And this is the region where the action potential that we are going to talk about or impulse that0509

transmits the signal from the dendrites here along down this axon, so this is the axon.0515

The action impulse is initiated here, action potential initiated here.0525

This is the axon. We will come back to this in a second.0540

And then, here at the end of the axon are the synaptic terminals.0542

We are going to look at a close up view of this later, but the neurotransmitter is released from the synaptic terminals.0546

Some nerve cells have myelinated axons, so what they have is what is called a myelin sheath that encases much of the axon.0562

Myelin in the peripheral nervous system is produced by Schwann cells.0579

Now, there are segments that are unmyelinated even on a myelinated neuron, and these are called nodes of Ranvier.0589

When I talk about action potentials, you will learn how the action potential really appears to skip from one node to the other in a myelinated neuron.0600

So, right now, I am just focusing on structure, and then, we will talk about function.0609

Here, you can see several nerve cells together, and these two nerve cells are synapsing on this nerve cell giving it input.0619

As I said, the neurotransmitters are released from the synaptic terminal here. They can, then, diffuse to the postsynaptic cell, give it input.0631

So, what I want you to understand here, is that these cells are called presynaptic cells.0644

Here, we have the synapse, this connection between one cell and another, and then, here, I have a postsynaptic cell.0655

Now, the nerve cell does not always synapse on another nerve cell. In fact, the nerve cell might synapse on a muscle cell.0671

So, what happens, then, is that the nerve cell is giving the muscle cell a signal to contract or inhibiting contraction.0681

Or a nerve cell can also synapse on an endocrine gland. It could, then, cause the endocrine gland to release a particular hormone.0693

There is communication not just obviously between one nerve cell and another but between the nerve cell and other systems of the body.0701

There are three groups of neurons.0712

The first group are the sensory neurons, and the sensory neurons receive information from the environment.0714

So, they receive input in the form of...it could be sound. It could be light, touch, smell.0729

And then, they transmit the input to the central nervous system to the brain,0742

to the spinal cord and to the brain for processing so that sensory input is received.0751

For example, when you look, your optic nerve is receiving that input of light, but it is your brain that interprets the image.0762

So, processing occurs in the central nervous system.0772

Information within the body is also collected: changes in blood pressure, changes in their stretch receptors in the GI tract.0775

So, the internal environment is monitored as well through the sensory neurons.0785

The second group of neurons are the motor neurons, and these transmit impulses to the muscle. They can, then, stimulate the muscle to contract.0792

Some motor neurons, as I mentioned, synapse on endocrine glands, so they might transmit to an endocrine gland stimulating a secretion of a hormone.0811

The cells that motor neurons act on...motor neurons act effector cells, so an effector cell could be a muscle for example.0824

You may have heard of Lou Gehrig's disease, also known as ALS, and this is a motor neuron disease.0840

It is degeneration of the motor neurons resulting in muscle atrophy and weakness throughout the body.0858

Finally, interneurons: interneurons connect sensory and motor neurons, so the input is being received by a sensory neuron.0866

Then, that signal may be transmitted to an interneuron which will, then, convey the information to a motor neuron.0886

These are also located in the central nervous system, the brain and the spinal cord.0895

And this is just giving you a very simple example, but the interactions between all of the different neurons are very complex.0901

But, in general, there are these three types, and this is how they interact.0909

Next, we are going to talk about how signals are transmitted by the nervous system.0915

And to understand that, you need to understand a concept called resting potential.0920

Just starting out talking about membrane potentials, a membrane potential is the difference in the electrical charge across the cell membrane.0926

So, if I have a cell and I am going to draw the cell here as a tube like if I am looking at the axon, the long axon membrane as a cylinder here,0936

there is a difference in electrical charge between the inside of the cell and the outside of the cell.0952

It is a result in a difference in concentration of ions between the inside and the outside of the cell.0959

The resting potential is the membrane potential of a neuron that is not conducting a signal, so that is why it is the resting potential. The cell is at rest.0967

So, the resting potential - this is the resting potential - is around -70 mV in the neuron.0978

And it is the result between the difference in sodium and potassium ion concentration inside and outside of the cell.0989

The concentration of sodium ions outside of the cell is much higher than inside of the cell, so lots of sodium outside, not so much inside.1000

The situation with potassium is the opposite. Lots of potassium inside the cell relative to the outside of the cell.1015

This gradient is maintained a couple of ways.1028

First of all, there is the sodium-potassium pump that I have mentioned elsewhere in the course.1031

What this pump does is it hydrolyzes ATP and uses the ATP for active transport of sodium out of the cell and potassium into the cell.1038

Three sodium are transported into the cell per two potassium.1049

Excuse me, correction. Three sodium are transported out of the cell per every two potassium transported into the cell.1061

So, when one ATP is hydrolyzed, the result will be per ATP hydrolyzed.1075

One ATP is hydrolyzed. That transports three sodiums out and two potassiums in.1082

So, here is this pump right here, and it is sending three sodiums out for every two potassiums in.1089

And this is active transport because these are being transported against their concentration gradients.1098

So, concentration of sodium outside the cell is much, much greater than sodium inside.1108

What the sodium wants to do is diffuse into the cell or not diffuse actually because it is an ion, but it wants to enter the cell. It wants to enter the cell.1119

It cannot though unless it goes through a channel.1128

Therefore, to get it out, you need to transport it against its gradient.1132

The concentration of potassium outside the cell is much, much lower than potassium inside the cell.1139

What potassium wants to do is it wants to leave the cell. To get it to enter the cell requires this active transport.1150

So, this maintains this concentration gradient.1158

Now, what happens is since these are charged, there also ends up being an electrical gradient.1161

So, this is a chemical gradient where we have lots of high sodium concentration out and high potassium concentration inside- chemical gradient.1170

But, this creates an electrical gradient, and let me talk about how this is created and maintained.1181

Well, for every three sodium out, only two potassium are pumped in. This is a net loss of +1 charge from the cell.1195

So, for every turn of the pump, one unit of positive charge is lost overall, a net loss of positive charge.1209

As a result, the inside of the cell ends up with a negative charge relative to the outside of the cell.1218

And this difference in charge ends up giving a membrane potential of -70 at rest.1232

The other issue here is that sodium channels...there are sodium channels.1245

And the sodium wants to go down its concentration gradient at the end of the cell.1252

The problem is these are mostly closed, so sodium channels are mostly closed. Meanwhile, many potassium channels are open.1258

So, what happens is some potassium can leave the cell, and that is a loss of more positive charge to make the cell negative.1275

Now, to balance this, chloride wants to follow so that the positive sodium leaving the negative chloride is going to go out with it.1284

And it will balance out in terms of charge. However, chloride channels are closed.1295

So, the positive charge sodium cannot really enter the cell.1301

The negatively charged chloride cannot leave the cell, but potassium, which is positively charged can leave the cell.1306

The result is we have more positive charge leaving.1315

We already have this in balance to the sodium potassium pump where we have more positive charge leaving the cell than coming in.1319

Now, we have more potassium leaving, and that causes this negative charge inside the cell relative to the outside.1324

What will happen is that there will be a net loss of potassium until the pull of the chemical gradient1334

of potassium is exactly counterbalanced by the negative charge pulling the potassium back in.1343

So, there are two forces acting on potassium.1352

There is a chemical gradient, which is drawing potassium out of the cell because potassium wants1354

to go down its concentration gradient to outside the cell where potassium is lower concentration.1362

So, the chemical gradient pulls - you can think of it as pulls - potassium out.1371

However, the electrical gradient, because potassium is negatively charged, draws potassium in, and these two are working in opposition.1379

And so, potassium will leave the cell until there is an equilibrium reach where the concentration gradient is no longer sufficient of potassium1391

- the chemical gradient - to oppose the attractive force, the negative charge drawing the positively charged potassium in.1402

That point of equilibrium occurs at about -70 mV, and that is the resting potential.1409

So, resting potential is a result of the selective permeability of the cell membrane for ions,1417

the fact that potassium channels are open but sodium and chloride are not.1425

And the resting potential is also maintain by the sodium-potassium pump.1431

What we say is that this cell is polarized. When we say that it has a resting potential, we say that it is polarized.1439

And I am going to talk about depolarization and hyperpolarization and repolarization.1450

And we are starting out with the cell that is polarized because of this difference in electrical charge compared with the inside versus the outside of the cell.1454

Now, I am talking about sodium channels and chloride and potassium channels, and these are a different type of channel that I am about to talk about.1466

I am going to talk again about sodium and potassium channels but a different type than I just discussed.1474

And these other types of channels are called gated ion channels, and these are key to understanding the action potential.1481

So in addition to the sodium and potassium channels I discussed, there are these channels that are gated.1489

Gated, meaning a stimulus triggers the opening or closing of an ion channel, so, gated means stimulus triggers the opening or closing of a channel.1498

And some of the channels that I talked about could involve some type of stimulus opening or closing.1520

But, I really want to focus on voltage-gated ion channels for the action potentials.1525

Voltage-gated channels would open or close due to a change in membrane potential.1532

So, these are regulated, the opening and closing of them is regulated by a change in membrane potential.1540

There are also what is called ligand-gated channels.1552

And in lagan-gated ion channels, opening or closing is triggered by the binding of a molecule to the channel.1556

So, ligand-gated, the stimulus would be binding of a ligand opens or closes the channel.1562

Extremely important in action potentials is voltage-gated ion channels.1578

These are sodium channels and potassium channels whose opening is controlled by changes in potential.1589

So, there are two types you need to be aware of.1597

The ones in orange are the sodium- voltage-gated sodium channels. The ones in purple are voltage-gated potassium channels.1600

This is a cell membrane, and this is the inside of the cell. Here is the outside of the cell.1610

Recall that outside the cell, very high relative to the inside of the cell concentration of sodium.1617

Inside the cell, the situation...and this is going to curve around the cell membrane1628

Inside the cell of the opposite, I have relatively high potassium, relatively low sodium concentration.1636

Opening these voltage-gated sodium channels causes a massive influx of sodium into the cell.1658

So, sodium is going to open up. Tons of these will open up once during an action potential, and the result is going to be sodium enters the cell.1665

When that positive charge enters the cell, it is going to make the cell less negative.1677

The cell was at -70 mV. If you put tons of sodium into the cell, it will go up to -50 and -40 and then, +10 and on up.1684

So, sodium enters the cell when these are open, and the result is the cell becomes depolarized; and I am going to put these all in context in just a minute.1694

Now, what is happening here actually these arrows should be going the other way. Let me go ahead and correct that, so correction there.1712

Now, what is happening is that since the concentration of potassium is very high in the cell relative to outside,1723

the potassium wants to go down its concentration gradient and leave the cell, and what that is going to do is cause positive charge to leave the cell.1731

When potassium leaves the cell the result will be the membrane potential will become more negative.1743

When the membrane potential becomes more negative, if it drops below the resting potential baseline, then, we say it is hyperpolarized.1765

Sometimes what is happening is that the membrane potential became plus negative due to depolarization.1774

And all the potassium is doing by coming back into the cell is resetting it to baseline, is repolarizing.1781

The thing you should understand is that sodium enters the cell. That causes the cell to become more positive inside.1788

That is depolarization.1794

When potassium leaves the cell, the cell becomes more negative inside.1797

That is positive charge leaving, and the cell becomes repolarized or even hyperpolarized.1802

An action potential transmits the signal along the axon of the neurons.1811

So, an action potential is also known as an impulse, and it is a large change in the membrane potential.1815

As you can see, this change down here is a quick increase where the membrane potential becomes more positive.1823

And then, it drops rapidly and becomes more negative and returns to its baseline.1832

So, here, at -70 is the resting potential, and I will give you an overview; and then, we will talk about what happens at each step.1837

As this is increasing, what we have here is depolarization. The cell is becoming depolarized until it reaches the peak.1849

Here, the cell is repolarizing, so it is repolarization.1866

It actually undershoots and goes past baseline, so the repolarization really tends to be a little more precise. It would be right around here.1875

And then, this segment here, when it passes rest, so repolarization is occurring as it is dropping, dropping, dropping and then, hyperpolarization.1888

The cell is depolarizing, becoming more positive, repolarizing, but then it shoots past the resting potential and then, hyperpolarizes briefly.1912

And then, it goes back to the baseline.1925

Let's look at what happens during each section here.1928

First, the cell is at rest. There is no stimulus.1931

Then, a stimulus excites the neuron and causes entry of sodium into the cell, and that can occur from a stimulus. It could be another neuron.1937

It could be light. It could be sound.1954

Some kind of stimulus excites the neuron, and it is going to cause sodium to enter the cell here.1956

Remember that when sodium enters the cell, sodium is positively charged.1962

So, these positive charges entering the cell are going to cause the membrane to become less negative.1969

It is going up, kind of, creeping up towards what is called threshold.1974

So, the stimulus causes the entry of sodium into the cell and causes some depolarization.1983

If the stimulus is strong enough, enough sodium will enter the cell that the cell reaches threshold.1993

If the membrane potential, the cell membrane, reaches threshold potential...let me put this right here, threshold.2004

If the cell membrane reaches threshold potential, then, the voltage-gated sodium channels open.2021

When the voltage-gated sodium channels open, that is going to be a massive influx of positive charge into the cell.2042

Here, you get some entry. Hopefully, it is enough to get you up to threshold, get things going.2050

But at this point, this is what we call all or none response that either you are going to get to threshold, and these are all going to open;2056

or you are not going to get to threshold, and none of these voltage-gated sodium channels will open.2069

If they do open though, there is going to be a very fast change in the membrane potential.2073

It is going to be more and more positive until it reaches a certain peak, and action potential is a stereotypic size and shape.2079

Even if you put a super strong stimulus, this is still going to peak at, say, 35.2086

It is not going to peak at 50, or it is not going to make the graph wider somehow or end up more hyperpolarized.2093

The size and shape are always going to be the same for a cell.2098

What is going to change though, is if there is a stronger stimulus, the action potentials will become more frequent, not larger.2101

They do not become larger.2113

Alright, now, the voltage-gated sodium channels have opened, big influx of sodium into the cell.2115

However, they quickly close. They quickly close.2123

So, then, the next thing that happens is sodium channels close, and here, voltage-gated potassium channels open.2127

Because right now, the cell has become depolarized.2149

The inside of the cell is now relatively positive and to end this action potential, we need to get back to the resting state.2154

Here, we have sodium rushing into the cell, then, the sodium channels close. The potassium channels open.2162

And potassium is going to go down its concentration gradient and leave. Potassium leaves the cell, so potassium rushes out of the cell.2172

During depolarization, we get sodium in.2184

During repolarization, potassium rushes out taking that negative charge with it, bringing the membrane potential back down, down to the negative range.2188

However, potassium continues to leave the cell not just until it hits this resting potential, but it does what is called an undershoot.2200

And at that point, there is hyperpolarization.2212

The cell has not just repolarized, it is actually gone past its hyperpolarized, and this section of the curve is called the refractory period.2217

And you cannot initiate another action potential during that time or during the latter part of it.2230

It is harder to initiate a potential, although, you maybe able to initiate it.2237

The reason that you cannot initiate an action potential during the refractory period is that the sodium channels remain closed.2241

And then, what happens is the sodium potassium pumps get to work and return things to normal, to baseline.2255

They cause return to the resting potential.2266

Initially, we had a stimulus triggering some entry of sodium into the cell.2273

So, the membrane potential becomes less negative, and then, if it hits threshold, the membrane potential's threshold is right around -50,2278

the voltage-gated sodium channels will open, and then, there will be a massive influx of sodium into the cell.2290

It will peak. The sodium channels will close, and then, the potassium channels will open.2299

There will be a massive influx or outflow of potassium from the cell. The membrane potential drops.2305

It undershoots. The cell is hyperpolarized.2313

That is the refractory period, a time during which an action potential cannot be initiated at all, or at certain points, it can be, but it is more difficult.2316

And then, as the sodium-potassium pump gets all this sodium back out and potassium back in, puts things back to where they were,2327

the cell will return to its resting potential state, and then, another action potential can be initiated.2336

The next thing is to talk about how action potentials are transmitted along the axon, and I am going to just draw a schematic.2346

Let this represent the axon.2357

A stimulus initiates the action potential at first, but then, that action potential initiates an action potential in a nearby segment of the membrane,2364

which initiates an action potential in the next segment and then, in the next segment.2377

This is often compared to having a row of dominos, and you push the first domino. That is the initial stimulus.2381

And then, that domino causes the next one to fall and the next one and the next one, and that is how an action potential is propagated along the axon.2387

So, remember at rest, what we are going to have is a relatively negative charge inside the axon and a relatively positive charge outside the axon.2396

The action potential comes along and switches that, so now, we end up with a positive charge inside and a negative charge outside.2409

The depolarization of the cell that causes this action potential is, then, going to cause depolarization in this nearby segment,2421

which will initiate the action potential there, which will open all those sodium channels and cause major depolarization, and that action potential gets going.2433

Meanwhile, this one is recovering from the previous. It has become repolarized, and it is returning to its resting state.2447

And now, it is going to be back at resting potential.2455

So, one action potential initiates another and so on along the cell, and in that way, the signal is propagated along the axon.2459

Now, the speed of conduction of an action potential is dependent on a couple of factors, so speed of conduction.2480

Larger diameter axon conducts more quickly. Myelinated axon conducts more quickly.2493

So, the larger the diameter, the less resistance there is. That action potential would be conducted more quickly along.2531

The other thing that can help is insulation.2539

Recall that Schwann cells produce myelin and the myelin sheet around the axon.2542

We have this long axon, and if it is myelinated, that serves us an insulator.2549

Let's say this is myelinated, and in between the myelinated segments are the nodes of Ranvier.2565

Conduction works like this on myelinated axons.2577

What happens is the electrical current moves quickly through these myelinated sections and then, initiates an action potential in the node of Ranvier.2582

The only place that there are the voltage-gated ion channels in a myelinated cell are in the nodes of Ranvier.2591

They are not exposed here, or they are not found in myelinated segments.2600

The current is going to connect quickly along these myelinated segments.2607

And then, when it gets to a node of Ranvier, it is going to initiate an action potential.2610

Current will travel through here, initiate an action potential and so on.2614

And so, it seems like what is happening is the signal is just jumping from one node to another to another.2617

And that is called saltatory conduction where what we have is saltatory conduction.2623

It is the action potential skips from one node to the next rather than being transmitted right from2630

one section to the next, to the next, to the next, as it would if the myelinated sheath were not there.