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For more information, please see full course syllabus of Anatomy & Physiology
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Lecture Comments (10)

1 answer

Last reply by: Bryan Cardella
Sat May 2, 2015 9:16 AM

Post by Hannah Hickerson on May 1, 2015

I'm excited to finish off the semester by watching your lectures and hopefully end strong by acing my Final exams. From what I've seen of you thus far I think these will help me tremendously.

1 answer

Last reply by: Bryan Cardella
Wed Feb 25, 2015 4:03 PM

Post by Ray Gaytan on February 25, 2015

Well, I will say "thank You." I enjoy your teaching methods. Great Job!!!!!

1 answer

Last reply by: Bryan Cardella
Sun May 18, 2014 11:53 AM

Post by Tom Hughes on May 17, 2014

What arteries supply the stomach, Pancreas and duodenum?

1 answer

Last reply by: Bryan Cardella
Tue Dec 10, 2013 9:50 AM

Post by Adriana Riano on December 9, 2013

According to the book by McArdle and Katch/Katch named Exercise Physiology seventh edition page 13 "A well nurished 80 kg man stores 500g of carbohydrates, of this muscle glycogen accounts for the largest reserve". This means that there is more glycogen stored in the muscles than in the liver. In your lecture you say the opposite or the opposite is understood.  Can you please clarify this?

1 answer

Last reply by: Bryan Cardella
Tue Dec 10, 2013 9:50 AM

Post by peter yang on December 9, 2013

your classes are really cool and funny

Digestive System

  • Functions of the digestive system include: ingestion, mechanical digestion, chemical digestion, secretion, absorption, and excretion
  • The alimentary canal (gastrointestinal tract) contains the mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus
  • The oral cavity (mouth) gets digestion started with the salivary glands (and saliva) along with the tongue and teeth
  • Deciduous (baby) teeth are shed during childhood and are replaced by 32 adult teeth
  • The types of teeth: incisors, canines, bicuspids, and molars
  • Tooth anatomy terms: enamel, dentin, pulp, gums, cementum, bone, nerves, and blood vessels (supplied to the root)
  • Swallowing a bolus of food involves the tongue, pharyngeal muscles, soft palate, and epiglottis
  • The esophagus is a muscular tube that moves food from the throat into the stomach
  • The stomach stores/breaks down food and has 4 major layers of tissue
  • Stomach anatomy terms: cardia, fundus, body, pylorus, sphincters, rugae, gastric pits, gastric glands, gastric juice (HCl, pepsinogen, pepsin)
  • The small intestine does a great deal of absorption, has 4 layers of tissue, and has sections called the duodenum, jejunum, and ilium
  • Intestinal villi and microvilli increase the surface area available for absorption of nutrients
  • The vermiform appendix is a small vestigial sac in the beginning of the large intestine
  • The large intestine is made up of the cecum and colon segments (ascending, transverse, descending, sigmoid) and its primary function is to reabsorb water and make solid feces
  • The rectum and anus are involved with the storage and elimination of fecal matter
  • The liver has many functions: organic compound metabolism, glycogen storage, waste removal, bile production, vitamin storage, breakdown of toxins, and removal of excess amounts of molecules from the blood
  • The gall bladder stores bile from the liver and sends it through a duct to the duodenum for emulsification of fats
  • The pancreas secretes digestive enzymes into the duodenum
  • Digestive conditions/disorders include ulcers, gallstones, hepatitis, and diarrhea
  • Did you know…
    • Q: How much fecal matter could the colon possibly store (if the rectum got backed up)?
    • A: The world’s largest colon on record is found in the Mütter Museum in Philadelphia, PA. The man who had this colon was born without adequate motor nerve networks in his large intestine, so his brain did not stimulate peristalsis to move along the forming fecal matter. By his early twenties, he was so backed up with fecal matter that he became known as “balloon man”. The preserved colon is close to 27 inches wide at its greatest circumference and stretches out to about 8 feet in length. Suffice it to say, he did not have a typical life span.

Digestive System

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  1. Intro
    • Functions of the Digestive System
    • Alimentary Canal (GI Tract)
    • Oral Cavity (Mouth)
    • Teeth
    • Swallowing
    • Esophagus
    • Stomach #1
    • Stomach #2
    • Small Intestine
    • Vermiform Appendix
    • Large Intestine
    • Rectum and Anus
    • Accessory Organs
    • Liver
    • Gall Bladder
    • Pancreas
    • Digestive Conditions / Disorders
    • Intro 0:00
    • Functions of the Digestive System 0:05
      • Ingestion
      • Mechanical Breakdown
      • Digestion
      • Secretion
      • Absorption
      • Excretion
    • Alimentary Canal (GI Tract) 1:38
      • Mouth
      • Pharynx
      • Esophagus
      • Stomach
      • Small Intestine
      • Large Intestine
      • Rectum
      • Anus
    • Oral Cavity (Mouth) 2:53
      • Salivary Glands
      • Saliva
      • Tongue
      • Teeth
      • Hard Palate / Soft Palate
    • Teeth 6:19
      • Deciduous Teeth
      • Adult Teeth
      • Incisors
      • Cuspids
      • Bicuspids
      • Molars
    • Swallowing 14:06
      • Tongue
      • Pharyngeal Muscles
      • Soft Palate
      • Epiglottis
    • Esophagus 16:41
      • Moves Food Into the Stomach Through 'Peristalsis'
      • Mucosa
      • Submucosa
      • Muscular Layers
    • Stomach #1 19:58
      • Food Storage, Mechanical / Chemical Breakdown, and Emptying of Chyme
      • 4 Layers: Mucosa, Submuscoa, Muscular Layers, Serosa
      • 4 Regions: Cardia, Fundus, Body, Pylorus
    • Stomach #2 24:43
      • Rugae
      • Gastric Pits
      • Gastric Glands
      • Gastric Juice
      • Gastrin, Ghrelin
    • Small Intestine 29:07
      • Digestion and Absorption
      • Duodenum, Jejunum, Ileum
      • Peristalsis
      • Intestinal Villi
    • Vermiform Appendix 32:53
      • Vestigial Structure!
      • Appendicitis / Appendectomy
    • Large Intestine 36:04
      • Reabsorption of Water and Formation of Solid Feces
      • Ascending Colon
      • Transverse Colon
      • Descending Colon
      • Sigmoid Colon
    • Rectum and Anus 37:48
      • Rectum
      • Anus
      • Hemorrhoids
    • Accessory Organs 41:13
      • Liver
      • Gall Bladder
      • Pancreas
    • Liver 41:40
      • Metabolism
      • Glycogen Storage
      • Waste Product Removal
      • Bile Production
      • Vitamin Storage
      • Breakdown of Drugs
      • Phagocytosis, Antigen Presentation
      • Synthesis of Plasma Proteins
      • Removal of Hormones
      • Removal of Antibodies
      • Removal of RBCs
      • Removal / Storage of Toxins
    • Gall Bladder 48:50
      • Stores Bile Made by Liver
      • Common Hepatic Duct
      • Common Bile Duct Connects to the Duodenum
    • Pancreas 51:28
      • Pinkish-Gray Organ
      • Produces Digestive Enzymes and Buffers
    • Digestive Conditions / Disorders 52:50
      • Gastritis
      • Ulcers
      • Gallstones
      • Cholera
      • Hepatitis
      • Jaundice
      • Cirrhosis
      • Constipation
      • Diarrhea
      • Lactose Intolerance
      • Gingivitis

    Transcription: Digestive System

    Hi and welcome to

    This is the lesson on the digestive system.0002

    Functions of the digestive system include ingestion, the act of physically putting food into your mouth that is ingesting.0006

    Mechanical breakdown starts in the mouth that is with the teeth, with the tongue.0014

    When you swallow food your stomach does mechanical digestion that is anytime you are ripping, tearing, crushing food.0020

    That is the physical breakdown.0029

    Digestion itself if you look at like what causes digestion to occur.0032

    Mechanical breakdown does assist with it but on a microscopic level it is the chemical breakdown that can get it done.0037

    That is enzymes, acids, all those molecules that physically breakdown macromolecules larger molecules into the tinier ones 0045

    that you can absorb in the bloodstream and provide body nourishment.0054

    Secretion throughout parts of your digestive tract all the way up in the mouth with saliva all the way down to large intestine you are secreting items.0058

    Glands are physically releasing substances, fluids, enzymes, other molecules, into digestive tract to assist with the breakdown and movement of this food to their.0070

    Absorption is the opposite of secretion.0081

    You are physically absorbing those nourishing molecules, those nutrients into your bloodstream so that you can stay alive.0084

    Excretion is releasing waste out to the exit.0092

    The alimentary canal is a fancy way of saying your digestive tract or your GI tract, gastrointestinal tract.0097

    Either of these terms or digestive tract is acceptable.0107

    When we look at this tube from the mouth all the way to the end, all of these are connected to each other.0111

    Some parts of it are little expanded or twisty turny are really long but all of these are in sequence.0117

    Later on I will cover the accessory organs that are off to the side of the tract like the liver and pancreas.0126

    It starts with the mouth, you swallow food goes down the pharynx right in here, and then into the esophagus.0132

    If it goes down into the larynx and trachea you have a problem and you could be choking or aspirating and that is no good.0141

    Once food and liquids go down the esophagus they enter the stomach.0148

    From the stomach we go through the small intestine, the longest portion, percentage wise of the GI tract.0153

    Then the large intestine which is large in terms of width not length which is right here, most of it is known as the colon.0160

    Then you will get into the rectum and anus.0168

    Let us start with the oral cavity which is the mouth.0172

    The starting of the chemical digestion of food is with the salivary glands.0176

    Even just seeing food on television or seeing a picture of food, smelling food, is going to initiate salivation.0183

    You have 3 pairs of salivary glands for total of 6.0191

    The parotid glands are in this region, in the sides of the cheeks.0196

    The sublingual literally means under the tongue.0202

    Some people can lift up their tongue and you can see these little holes and they squirt like little hoses.0206

    Those are the sublingual under the tongue salivary glands.0213

    Sub mandibular which are deeper and associated more with the mandible.0216

    There is this mandibular groove that is next to the back of the teeth where these particular salivary glands are rooted.0221

    The majority of saliva comes from the sub mandibular glands and the rest of it from the parotid and sublingual.0230

    Of course salivary glands release saliva.0237

    What is in saliva?0240

    The vast majority of it is water but what is the other 0.6%?0241

    You are looking at enzymes, antibodies, even white blood cells on occasion.0245

    But the enzymes are what we are going to focus on.0253

    Salivary amylase is what we will it is one of the main ones that break down larger carbohydrates into tinier ones like glucose and galactose.0257

    Those are monosaccharide.0267

    Lysozyme is an enzyme that actually helps keep the bacterial populations in your mouth at acceptable levels.0268

    Everyone has bacteria in their mouth even using a really good mouthwash you are going to get rid of all of them.0276

    It is important to have some bacteria in your mouth that is normal.0283

    You do not want them to get out of control.0287

    Out of control bacteria is going to lead to infections like gingivitis, tooth decay, periodontal disease, things like that.0289

    Lysozyme is an enzyme that helps keep that bacteria population in check.0297

    Your tongue has a lot to do with getting the food swallowed and to help break it down.0304

    As you chew your tongue is a very strong set of muscles that work together and overtime your tongue is so strong 0312

    that you can actually end up moving your teeth in the long run if your tongue keeps pushing on them.0321

    The teeth have a lot to do with mechanical digestion or the physical breaking down of food products.0327

    Teeth are not technically bones.0335

    They are structures a bit different than the bones of body.0337

    I am going to cover that in the next slide.0340

    The hard palate and soft palate.0341

    In this particular image, this sagittal cross section straight through here.0344

    There is a little bit of germs in this image but on here is the hard palate right here.0349

    A lot of it is actually the maxillary bones and the palatine bones.0355

    If you go posterior to there you have got the soft palate where that uvula hangs, that thing that looks like a punching bag in the back of your mouth.0363

    The soft palate has a lot to do with the swallowing which we are going to get to in a bit.0372

    First we are going to start off with the anatomy of teeth.0378

    I am going to start by mentioning dentin and I am going to erase this because this image is dentin but you actually see the word dentin much more often.0383

    Dentin is a lot of the mass of the tooth and that is not quite on the superficial level like an animal.0402

    It is a bit deeper.0410

    Dentin is similar to bone but the reason why we would not consider bone is unlike your skeletal bones there are no cells in dentin.0410

    If you look at any bone in the body there are cells that help regulate what is going on your bones and help produce additional bone matrix overtime.0421

    Dentin does not have cells in it.0431

    Superficial to dentin you have what is called the enamel.0433

    Enamel is the hardest biological substance in the human body.0437

    There is nothing else in your body that is harder than this.0441

    That is important for protecting you outside of your tooth.0446

    Not just the mechanical wear and tear on teeth but the acidic substances that enter your mouth.0449

    If it was not for the enamel you will be getting much more wearing away of these tissues deeper in the tooth.0455

    Overtime enamel can wear by eating too much acidic food, chewing on things that are way too hard too often can damage your enamel.0463

    I have lost some enamel in my teeth because I tend to grind my teeth in my sleep.0473

    I do not that as much as I used to, I wear a mouth guard now but over time that is additional wear and tear that you do not want.0478

    Deeper to the dentin is the polp layer.0486

    It is where you are going to find the nerves associated with teeth and blood flow into the tooth.0490

    As you can see there are tiny little arteries and veins, capillaries associated with each tooth.0496

    There are also nerves associated with the polp.0505

    Here are the roots of the teeth.0508

    Depending on the tooth we are looking at the amounts of roots can vary.0510

    Some teeth have only one root.0513

    Some have 3 or even 4 roots.0515

    Cementum is a structure that helps keep the tooth anchored in the gum or the gingiva is the other term for the gums.0517

    If it was not for cementum the chances of losing an adult tooth would drastically increase.0526

    Thank you to cementum which is like cementing the tooth in place.0533

    Here is the bone of tooth that is anchored in.0537

    That bone is either going to be the mandible or the maxillary bones.0539

    There are nerves associated with every tooth as well.0544

    The crown is what emerges out from the gum of the tooth.0549

    When you look at the teeth in a baby vs. teeth in an adult, babies get their deciduous teeth also called milk teeth or baby teeth depending on who you are talking to.0554

    Deciduous means falling out like of deciduous trees lose their leaves in the fall.0565

    It is the same meaning.0571

    Those baby teeth are supposed to fallout.0573

    They typically start falling out by the time you are 7 or 8 years old and making keep falling out through high school or higher grades.0575

    Even as some adult people still have deciduous teeth.0585

    It is not that common but you tend to get around 20 deciduous teeth that can vary slightly depending on the person but 20 is about average.0589

    By the time you are an adult and you have lost all your deciduous teeth and you have gained your adult teeth you should have 32.0596

    That number can vary as well because I no longer have 32 adult teeth.0604

    I actually got some of my teeth removed which I am going to get into a moment.0610

    Incisors are the ones that are right at front here.0613

    4 incisors and the 2 big ones here and 2 that is right under them.0617

    Incisors tend to have one root and they tend to have that structure that is kind of broad and flat.0624

    When you bite on something that you are sticking in your mouth, incisors are going to be the first to may contact typically.0632

    Cuspids also known as canine teeth, you have a total of 4 of them.0639

    If you count top and bottom, they are right on the sides of the incisors.0647

    My canines are not as sharp as they used to be because like I told about grinding my teeth that literally wore away the sharpness of my canines.0652

    Some people’s canines are sharper than others.0661

    These also attend to have one root.0663

    Bicuspids is a little further not quite to the molars but bicuspids have 2 cusps meaning 0666

    when you look at the surface of them it looks like they have 2 points instead of 1 point like a canine.0674

    Bicuspids can have that kind of a double root like this.0680

    Molars, all the way in the back on the top and bottom, the molars those can have numerous points.0685

    They tend to be broader, more from grinding of plant material.0694

    If you compare different animals in the animal kingdom, animal like a giraffe which eats plant material totally, 0699

    you are going to see teeth in its jaw that resemble our molars.0707

    But they are going to be a whole surface.0711

    In the very front of a giraffes mouth you will have teeth that resemble the front of ours but the majority of teeth are meant for grinding that plant material.0714

    When you look at something like a canine, a dog, it is no coincidence that they are called that because they have much more sharp teeth for tearing flesh0725

    because they tend to hunt and kill live animals.0734

    We are meant to be omnivores meaning eating animal materials and plant materials instead of one of the other.0738

    That is why we have that variety as humans.0748

    We have some sharp teeth and some flatter, broader teeth for both kinds of foods.0750

    When I said I do not have 32 teeth any more, I got all four of my wisdom teeth removed and that is a term for teeth in the back.0757

    Some people do not get all 4.0768

    Some people who are born with less it is just a genetic factor or maybe having something to do with the development of the womb.0771

    My wisdom teeth as they were coming in when I was in the early high school I was about 15 they were impacted.0778

    Meaning as my wisdom teeth are coming in the last of my adult teeth they were pushing against the other teeth.0789

    Let us say this is a molar that was not quite in the back.0796

    And here is the gum line and there will be another tooth over here.0803

    But the back part, the more posterior portion part of my jaw has a tooth that wanted to grow in this way like I was pushing on my molars.0810

    The dentist said that if we let this continue its path overtime they are going to keep pushing on those molars that are close to the front 0824

    and can cause a lot of pain and discomfort and can actually disrupt the placement of your teeth.0832

    They went in and remove all 4.0838

    I actually have 28 adult teeth instead of 32.0841

    When it comes to swallowing there are four main contributors to the action of getting food that you have been chewing up 0845

    and salivating on back into your pharynx and esophagus.0853

    The tongue is the major contributor.0858

    If you look at what happens in the sequence in the sagittal depiction you can see that this is the tongue here.0861

    The tongue as you swallow it tends to brush up on the palate, most of the hard palette and push backwards.0868

    Swallow right now and see what your tongue is doing.0876

    I just felt to do that.0880

    It just kind of brushed back and it makes this action that physically pushes that bunch of food that you have been eating 0882

    or the liquids that you put in your mouth back down your pharynx.0889

    The pharyngeal muscles as you swallow you can feel that there are muscles located in here that also tend to move parts like the soft palate and the epiglottis.0893

    The soft palate is right back here and you can see that it does move as you push bowls of foods backwards.0905

    The soft palate kicks up to provide that clump of food that is why it is called bolus to move back.0912

    The epiglottis also makes an action every time you swallow you can feel your larynx arch up and back.0921

    The epiglottis or this little flap right here closes on top of the glottis.0929

    You can see that here.0934

    If it was not for this epiglottis closing this food bolus could potentially go through the glottis and into the larynx and trachea.0936

    That would be no good.0943

    You want to go through that posterior passageway, the esophagus, down to the stomach.0944

    Speaking of the esophagus right here they label upper esophageal sphincter that is the muscular doorway to the top of the esophagus.0951

    In British English there is an O in front of the esophagus.0959

    In American English there is not.0964

    One of the main differences between those two forms of English but this is the step by step process of what happens when you swallow a chunk of food.0966

    You notice that once the food has done pass the glottis, once that swallowing action is over the epiglottis 0975

    will come back up allowing you to breathe adequately in and out until you swallow again.0984

    The amount time it takes for food to get all the way the esophagus and the stomach is about 9 seconds.0990

    It depends but that is average.0996

    When we look at the esophagus, the esophagus here is a hollow muscular tube approximately 25cm long and at its widest portion about 2 cm wide.0999

    Moves food into the stomach through peristalsis.1012

    Peristalsis in general is a wavelike muscular contraction.1017

    Any tube that has a muscular lining that needs to move something through in your body it is usually not conscious voluntary control.1022

    It is an unconscious thing involuntary that moves food through or in other cases we look at the internal female anatomy 1032

    peristalsis happens in the fallopian tubes to help move an egg through meet sperm.1041

    In this case we are talking about moving food from after the swallowing action down to the stomach.1048

    Once you swallow your voluntary control is done.1055

    I cannot physically move it fast down my esophagus or physically move into my stomach more quickly.1058

    It just happens naturally.1066

    That action is called peristalsis and they are these wavelike muscular contractions that move food down.1068

    No absorption happens in the esophagus.1075

    Yes items are secreted, there are lubricating secretions into the lumen but the space in the esophagus to help ease food down but you do not do absorption of nutrients here.1077

    The first place that happens is actually in stomach and then further down.1091

    The major layers in general when we look at the digestive tract there are 4 major layers.1098

    You will see 3 significant layers hear and I will mention the 4th layer in a moment.1103

    But the innermost layer or deepest layer of esophagus is the mucosa.1108

    Think of mucus that secreting stuff that is in the innermost parts.1112

    The mucosa layer deepest, sub mucosa just superficial to that.1116

    It is a supporting layer for the mucosa but some mucosa oftentimes can have blood flowing there.1121

    Lymphatic tissue as well which has to do with protection and immune response.1128

    The muscular layers are superficial than that and without the muscular layer you are not going to get that peristalsis happen to move food and liquids down.1134

    There is an additional layer when you look at the stomach and further on down the GI tract it is called the serosa.1143

    The serosa is absent from the esophagus.1150

    You do not see significant serosa there but the advent tissue, that layer of tissue on the superficial most part of the esophagus 1154

    does have connective tissue that anchors it to the dorsal body wall.1163

    The esophagus is really close to your back.1169

    It is close to the spinal column, the vertebrae of your spine.1171

    You want to keep your esophagus anchored.1176

    You do not want it moving around within your body.1178

    You want it to stay in put.1182

    In general serosa and the other parts of the digestive tract allow connection of those organs to the organs around them 1183

    and also provide stability for the outer part of the organ.1193

    Once you have threw liquid exiting the esophagus it is going to go into the stomach.1197

    Right here at the top is something called the lower esophageal sphincter.1204

    It is the lower part of the esophagus and the sphincter is a muscular doorway into the stomach.1209

    It is not very tight.1215

    In some animals it is much tighter.1217

    I have heard that horses their sphincter is very tight and they are unable to vomit.1220

    You want it to be tight enough to keep the food digesting in the stomach but if you have eaten something that is not good for your body 1224

    or too much is something your body sometimes has a need to expel.1234

    We will talk more about the vomiting reflex in a bit.1238

    But in general the stomach is a J shape organ meant for storage of food temporarily.1241

    Mechanical and chemical breakdown and emptying of chyme into the small intestine.1247

    Chyme is a mixture of gastric juice produced in the stomach and your partially digested food.1252

    A lot of digestion happens in the stomach.1258

    It can happen further on down as well.1260

    Chime is exiting the stomach into the small intestine on a daily basis.1263

    In terms of mechanical and chemical breakdown, mechanical is the physical movement that mashes or crushes something.1270

    The stomach is filled with muscles that churn and your stomach does that while you are not thinking about it.1279

    Of course a lot a chemical breakdown happens in the stomach as well through gastric secretions.1286

    Gastric always means stomach.1291

    4 layers like I have mentioned earlier.1294

    Mucosa is the most deep layer without mucus is coming.1297

    Sub mucosa is the supporting layer just superficial to that.1300

    That is going to have the blood flow and lymphatic access and also nerves going in there.1304

    Muscular layers those are connected in nerves because without stimulation of the muscles to contract they are not going to move.1311

    You actually have 3 different orientations of muscles.1320

    You have circular muscles, longitudinal muscles, oblique muscles, wrapped around the stomach in various ways that maximize the ability of it to churn.1325

    The serosa is the outermost layer on the outside.1337

    The most superficial layer that is protective and helping to anchor the stomach in place.1341

    The stomach is slightly to your left.1346

    People oftentimes touch this part of the abdominal area they are really touching where their abdominal muscles are and where it is mostly small intestine bundled up.1349

    The stomach is actually superior to that and slightly lateral off to the left.1359

    Your liver is slightly to the right.1366

    The 4 regions of the stomach are the cardia, fundus, body, and pylorus.1369

    You can see the labels here in this image from Gray's anatomy.1373

    The cardiac portion has to do with the area the stomach that is adjacent to that esophageal opening.1376

    The fundus is the part of the stomach that actually lies just superior to the opening.1382

    The body is this area here that is where food tends to rest where chyme is going to be built up.1390

    It is a very acidic mixture of gastric juice and partially digested food.1399

    The pylorus is the part of stomach that leads to the pyloric sphincter which is the opening into the small intestine.1405

    One more thing I want to mention before moving on is of the pyloric sphincter, its closing and opening is very important 1414

    because having food stay in the stomach not only is good for breaking it down further 1421

    and making it easier for your small intestine to break it down and absorb.1428

    But also a disorder has been discovered in certain people who tend to become obese.1433

    The small percentage of population they have a disorder where their pyloric sphincter is too loose.1439

    It lets food exit the stomach too quickly.1446

    You want food to stay in the stomach for a little while because there is a signal that goes to your brain that say you have eaten enough you can stop eating for now.1449

    This meal is over effectively.1458

    But if food is exiting the stomach out to the pyloric sphincter too quickly your brain has no time to get the signal and these people tend to overeat.1459

    An operation that tightens the pyloric sphincter can actually help them better regulate their appetite.1469

    It is an interesting discovery pertaining to the pyloric sphincter and the tendency to become obese.1475

    I have just mentioned this about the lower esophageal sphincter right there at the bottom of the esophagus.1481

    Here is my pyloric sphincter.1494

    The lower esophageal sphincter up top is going to be right here.1496

    That doorway to the stomach and here is the doorway out of the stomach.1507

    If you look carefully in the mucosa layer of the stomach on the inside there are these little folds call rugae.1512

    These folds increase the surface area within the lumen or the space in the stomach.1520

    Just like in other parts of body where see increase surface area, more tissue means more absorption, more secretion.1525

    Having it all these rugae maximized the ability of the stomach to release gastric juices for digestion.1533

    Also as the stomach expands the more food you put it on, the rugae when they stretch out that allows greater expansion of stomach with ease.1541

    Gastric pits are these little holes in the rugae where you are going to get gastric secretions.1551

    In those pits you find gastric glands.1557

    The 2 main cells apart from these gastric glands are parietal cells and chief cells.1561

    Parietal cells have a lot to do with the release of hydrochloric acid into the lumen of the stomach.1566

    We can call the mixture of this and other things gastric juice.1575

    The interesting about parietal cells is if they produce and made hydrochloric acid with in the cytoplasm within the inside of that parietal cell, 1579

    that hydrochloric acid be enough to physically damage the parietal cell and break it down.1591

    It is doing enough the parietal cells send out the H+.1597

    If you go to chemistry HCL is made of H+ and Cl-.1602

    This particular cation and this anion together make hydrochloric acid.1611

    When they are separated it is really not hydrochloric acid.1617

    The parietal cells send out the H+ and the Cl- separately and then they join together once they are getting out of the gastric pit and together in the stomach.1620

    That hydrochloric acid has a lot to do with digestion and in keeping the acidy of stomach high.1636

    Amazingly on there is an alkaline buffer.1641

    Alkaline meaning basic the opposite acidic that keeps the stomach from digesting itself.1646

    That buffer is good for the stomach not wearing away overtime.1652

    When we look at chief cells, chief cells secrete a substance known as pepsinogen and pepsinogen is broken down in to pepsin because of the high acidity of the HCl.1657

    Pepsin is an important part of gastric juice for digesting proteins and getting it broken up into little bits of amino acids 1675

    that eventually going to be absorbed primarily by the small intestine.1683

    The stomach does some absorption but the main absorber, doing the majority of the absorption for the digestive tract is the small intestine.1688

    Gastrin is one of those hormones that has a lot to do with the functionality of the stomach.1696

    Grolin is a hormone that you do not read or hear a lot about.1703

    In older anatomy textbooks when I took anatomy early on in my education I did not hear about this grolin hormone.1708

    But there is more research these days to what this does.1719

    This is a hormone released by the stomach that tells the brain we are hungry or we are not.1722

    The more grolin that is released the more the brain feels we are hungry and we need to eat.1731

    Once food enters the stomach and the stomach has expanded off, the amount of grolin is reduced and and do not feel as hungry.1737

    After the stomach is the small intestine.1745

    It plays a key role in digestion and absorption as there is further breakdown that happens here but a lot of absorption going on as well.1750

    The small intestine amazingly if you are to stretch it and ends up being about 18 feet long sometimes 20 feet long in the average person.1758

    And that is longer than the tallest person who ever lived ×2.1768

    That is amazing to think about that there is that much intestine bundled up right here.1773

    There are connective tissues keeping it tight to itself in a little bundle.1779

    There are 3 main segments of the small intestine.1784

    The duodenum, the jejunum, and the ileum.1787

    This is an order from this part being adjacent to the stomach to this part being adjacent to the large intestine.1790

    Once again peristalsis, the muscular lining in the small intestine is going to help move that kind from 1796

    the stomach all the way through that 18 feet length eventually into the large intestine.1804

    4 layers as before.1810

    It is 4 layers of the stomach.1812

    The mucosa, sub mucosa, muscular layer, and serosa.1814

    You would find those in the small intestine as well.1818

    We are going to focus on the mucosa and what that lining looks like.1821

    If you are to take a cross section through the tube of your small intestine and look down it like you are looking down a barrel.1826

    You would see these little finger like projections called villi.1833

    Here is the lumen and that is the space right in their but each of these is a villus.1839

    Villi is plural.1844

    Villus and all of this is villi.1853

    That little finger like projections.1855

    When you zoom into one of them so here is one of those villi, if we zoomed into the surface of one single villus 1857

    there are little tiny microvilli on each of the cells of this epithelium.1870

    Here is a layer of epithelium that goes all the way around the border.1877

    And this just further increases the surface area.1881

    I have heard that the surface area and all of your small intestine, if you open up all of that surface area and laid out flat like you were tiling a floor. 1884

    It would be close to the square footage of a comfortable 4 bedroom home.1899

    That is amazing to think about that is all in your small intestine.1904

    Each of these of villi have microvilli that further increase the ability to breakdown chemically the chime, 1907

    the digested food that is coming in and to absorb it effectively into each of these villi.1917

    Each of the villi and micro villi are in the border.1923

    You are going to have blood flow.1927

    Blood flow coming into here that is how you get it into your bloodstream.1930

    The nutrients into the bloodstream and are delivered to all the cells.1935

    You also have something called a lactile.1938

    This green projection, this lactile enables your lymphatic system, the immune system to have access to these villi.1941

    That is important in the case something traveling through your digestive tract is a potential harm in terms of it containing bacteria or viruses. This lactile is another way that your body can defend yourself from foreign particles or pathogens that entered your digestive tract.1952

    When you get to the end of the small intestine and later on we will come back to how bile factors into the small intestine through the breaking down of fats.1971

    But when you get to the very end of the small intestine, the ileum, you have reached the appendix.1984

    You can see from this Gray’s anatomy diagram here is the ileum and this is the end of the small intestine.1993

    Here is the entrance into the colon or the large intestine.1998

    Here is what is called the vermiform process or vermiform appendix.2003

    Vermiform means worm like.2008

    It does look like a little worm.2010

    The appendix is a small worm like sac located near the opening into the colon or large intestine into the vestigial structure.2013

    If you took biology, the vestigial structure is kind of like a remnant of some part from an ancestor that is reduced in size and it is of less importance.2020

    Sometimes it is completely useless.2031

    There are different theories about how useful the appendix is.2033

    The best theory I have heard is that we still have this left over from one of our ancestors from millions of years ago.2037

    If you look back at the anthropological record or if you were to ask a paleoanthropologist or somebody who specialize in the fossils of human ancestors,2045

    they will tell you that some of the ancestors getting that made years ago did not eat cooked meat.2055

    They ate vegetation but they also eat animal tissue without cooking it.2062

    You are introducing a lot more bacteria into your body by not cooking on animal meat.2067

    They think that this particular sac was a bit larger in those ancestors and that was conducive or helpful to the process of digesting that raw meat.2075

    Overtime, when our ancestors finally started cooking meat that changes the proteins in terms of breaking down some of that stuff prior to putting it in your body prior to ingesting it.2086

    It also kills all the bacteria so we think that the size of this has gradually been reduced over millions of years.2099

    Maybe one day in our descendants it could be gone.2106

    It is hard to say how long will take that to happen.2110

    But the interesting thing is that when you do get it removed because of infection many doctors will caution the person 2113

    and say now that we have removed your appendix it is a good idea that you do not eat sushi right away or be careful with introducing raw animal tissues2120

    because you are more sensitive when you are missing appendix.2132

    Many people differently on depending on who the person is but an appendicitis is an infection of the appendix.2135

    Too much bacteria inside of their can cause it to swell up and get it inflamed where it pops, it bursts and that could kill a person.2141

    An appendectomy is the removal of the appendix.2152

    Since it is vestigial, since it is typically not needed there is no harm in removing the appendix.2156

    The large intestine begins right here and it kind of loops around where the small intestine is located right middle here.2162

    It includes the cecan which is the initial part right here and the colon segments.2173

    It is for the reabsorption of water.2178

    It makes your feces, your wastes solid.2181

    That is why I say your formation of solid feces is the primary function because when you get diarrhea that means 2187

    that your large intestine is not doing the job it should be doing of sucking water out of the lumen and making feces solid.2194

    Diarrhea is excessively watery feces.2202

    It is uncomfortable.2205

    You do not feel good and that is because some bacteria or virus is inhibiting your large intestines ability to do its job.2206

    Beyond that, other nutrients are absorbed in the large intestine.2214

    It is not just absorbing water out of it.2218

    Some nutrients are absorbed in large intestine but far less than in the stomach in the small intestine.2222

    The 4 regions are the ascending colon, since this is rising up on the right side of your body ascending.2227

    Transverse it goes across horizontally right under where the liver is and then stomach.2235

    The descending colon right here it descends and physically moves down.2242

    As you move through these segments more and more water has been sucked out of it since it is supposed to happen to the point where we get to the sigmoid colon.2246

    This S shaped curve by the time you get to the rectum where feces are stored hopefully it is solid feces ready for excretion.2256

    The rectum is that last 15 cm in the digestive tract right in here.2267

    Here is that sigmoid colon and it is for storage of feces.2274

    Storage of feces, in terms of evolution dates back to having a planned and intentional disposal of your feces in certain areas to mark your territory.2278

    You do not want it to be constant letting go of waste because when a predator was trying hunt you, you are better be able to track you.2291

    The timed elimination and control of one feces dates back to that.2300

    The storage of feces happens in the rectum and eventually you get down to the anus that muscular doorway where feces are expelled through.2305

    The anus, exit of feces happens there.2317

    There are 2 anal sphincters or 2 sets of muscular doorways.2320

    The internal anal sphincter is a little bit deeper in terms of being internal in your body is involuntary.2324

    You have no conscious control over it.2332

    As the rectum fills up you are going to get a loosening or relaxing of the internal anal sphincter in response to the crowding of feces.2334

    Once it gets too full it is time to let it go.2345

    You do have control over your external anal sphincter.2348

    When someone is actively trying to hold in feces they are contracting the external anal sphincter and the relaxing of that is going to let feces through.2352

    Hemorrhoids happen when there is too much irritation of the blood vessels that are around the rectum in the anal region.2363

    That causes dilation or swelling of those blood vessels.2372

    As hard feces move pass them or as they are pushed past forcefully it causes bleeding.2376

    These enlarged blood vessels bleeding are not very comfortable, not very healthy in the long run.2385

    The way that you can minimize the occurrence of hemorrhoids and bleeding in that region is to get fiber in your diet.2392

    Fiber helps keep your feces a little softer.2399

    Really hard feces can happen when you do not use much plant products.2404

    We do not use much fiber and the meat content a little too high that leads to really hard feces which are rubbed on these walls much more.2408

    Also drinking more water is going to help and not pushing when you are in the toilet. Pushing on the toilet is going to irritate the walls of this part of the digestive tract.2419

    Making it more likely they are going to develop hemorrhoids and that bleeding will happen.2430

    By the way hemorrhoids can be removed surgically.2434

    That is typically not done unless they are severe.2438

    If you do have hemorrhoids see a doctor and they will test to make sure that is all it is.2443

    That is just hemorrhoids because blood in your stool or fecal matter in the toilet could be a sign of colon cancer.2448

    Definitely get that checked out.2456

    They will do colonoscopy which is where they actually move a camera up through the large intestine to see if there are growths of polyps.2458

    They will take tissue samples of them to see if they are cancerous.2469

    We have covered the digestive tract.2472

    The GI tract or alimentary canal we are talking about the accessory organs that are off to the side but are very important in digestion.2476

    The liver is one of them.2485

    The gallbladder which is tucked underneath it this green sac.2487

    The pancreas is hidden in this image because it is a little bit behind the stomach.2491

    A little bit behind the large intestine but there is right there that yellow organ.2495

    The liver this the first line of the liver.2500

    It is the largest visceral or internal body organ.2503

    The largest one will be the skin.2506

    A significant sized organ is slightly off to the right side of the superior part of your abdominal cavity.2508

    2 lobes here is one, the larger one is on the right and this one a little bit more centrally located.2517

    They are separated by fossil form ligament.2523

    It is like a white band in between the two deep dark reddish portions of the liver.2527

    One of the reasons the liver is such a deep dark organ is the high amount of blood flow.2533

    There are a lot of blood flow deliver all throughout the day.2538

    If you take all the blood out of liver and look at that organ from a dead body, it still has a reddish purplish tone.2541

    When it is a living being it is very red as an organ.2550

    About 25% of your blood in any given moment could be in the liver.2554

    Hepatocytes are liver cells that word hepato always pertains to the liver and are located within lobules.2559

    If you take a cross section of liver and look at what is in it with a microscope there are these little round regions called lobules.2566

    In there you have hepatocytes.2577

    You have lots of blood vessels.2581

    You have lymphatic tissue in these little clusters.2584

    That is how the livers are arranged microscopically.2588

    The major functions of the liver.2591

    It is no coincidence that it is called the liver without it you are not going to live.2592

    It has many functions.2597

    Carbohydrate, lipid, and amino acid metabolism.2599

    It assists with the breaking down of all of these macromolecules, all these different organic molecules that you eat on a daily basis.2603

    It also has to do with the storage of glycogen.2612

    Your glucose levels in the bloodstream have a lot to do with the action of your liver.2616

    Glycogen is a large polysaccharide.2622

    It is like analogous to starch in plants.2625

    Starches help plants to store sugars.2630

    We store it as glycogen.2632

    If you have not eaten in a long time or maybe you are gone for a long run, your blood sugar levels might be low.2634

    Your liver is stimulated to break down glycogen in individual of glucose is that are sent into the bloodstream.2642

    You also do store some glycogen in your muscles but there is a lot of it in your liver.2649

    You also do store lipids and overtime one way that you can get too much lipid storage in your liver is abuse of alcohol can lead to developing a fatty liver.2654

    The liver get enlarged and take on a whitish appearance because of excess lipid storage 2668

    and in the long run than enlarged liver can eventually lead to cirrhosis which I will get to in a bit.2673

    Waste product removal, the removal of waste from your bloodstream happens significantly in the liver.2681

    Bio production, bio which we will talk about more in a little bit with the gallbladder has to do with the emulsification of fats.2688

    Breaking down of fats into tinier bits and makes it easier for enzymes to break them down and absorb them.2697

    Vitamin storage, A, B, K, B12 these vitamins are stored in the liver.2703

    You need to consume those in your diet that is a matter of keeping yourself healthy.2712

    If you do not get enough in your diet you are going to be releasing them out of the liver to supplement your cells with those particular vitamins.2718

    Breakdown of drugs, alcohol, drugs, whether legal or illegal your liver is breaking them down.2725

    The reason why some medications that are prescribed need to be taken once a day or four times a day it has to do with the speed at which the liver breaks down the drug.2731

    My dad worked for a pharmaceutical company that figured out that if they just added a certain molecular component to the drug 2743

    they already made it would slow down the livers ability to get rid of it.2751

    To physically break it down and eliminate it through waste in the body.2756

    Just adding that little molecular component made it so that you only had to give one injection of this drug per week instead of once a day or multiple times a day.2760

    The liver has its own pace with breaks down alcohol, with breaks down drugs, and that has a lot to do with genetic factors and tolerance of the drug over time.2773

    More on the liver.2783

    Phagocytosis and antigen presentation.2787

    This is a part of your livers ability to assist with your immune system.2790

    Phagocytosis not just of foreign bodies that are coming into the liver through the blood flow but also swallowing up red blood cells that are damaged.2795

    The phagocytosis are eating of red blood cells and breaking them down.2807

    Your liver assists with presenting antigens usually protein components on the surface of foreign invaders or pathogens to assist with your immune systems ability to kill those things.2810

    Synthesis of plasma proteins.2823

    Blood cells are made typically in a bone marrow but a lot of the proteins that end up in the fluid of your blood up are produced in the liver.2825

    Removal of hormones.2835

    Hormones release from all different endocrine glands throughout the body but your liver has lot to do with taking in excess adrenalin, insulin, 2837

    and removal of those hormones from the body when they are no longer needed.2846

    Removal of antibodies.2850

    Antibodies are supposed to be in your blood stream at certain times.2853

    Other times they are removed.2859

    Antibodies allow white blood cells to adequately and efficiently attack foreign invaders.2860

    Antibodies the amazing thing is when your liver takes them in through removing from your bloodstream, 2867

    your liver can break down the antibodies into individual amino acids because antibodies are made of protein.2872

    Your liver can reuse those amino acids to make other proteins.2878

    For instance plasma proteins, they can recycle those little bits.2883

    Like I have mentioned earlier the removal of red blood cells are very important.2886

    The breakdown of those red blood cells is going to lead to the formation of bilirubin which has been discussed in other lesson that I went over.2890

    The removal /storage of toxins.2901

    The stuff in your bloodstream that does not belong there.2903

    Toxin substances the liver is going to remove that.2907

    One example is hydrogen peroxide.2909

    There are so many things the liver can remove but hydrogen peroxide is broken down by enzyme called catalyst.2913

    The liver of every living being not just humans contains catalyst, the enzyme that breaks down H2O2.2921

    Next is the gallbladder.2929

    Gallbladder stores bile.2932

    The liver produces bile and then sends it to the gallbladder.2934

    That is located just inferior to liver.2938

    Here is an inferior view from underneath the liver.2942

    You can see that there are these hepatic veins or hepatic means of liver.2946

    These veins that are helping to take blood from the liver to go back to the heart.2950

    Here is the inferior Vena Cava that is the major vein that is going back to the right atrium.2955

    The common hepatic duct is what is going to take bile from the deliver to the gallbladder and then the common bile duct connects the gallbladder to the duodenum.2963

    The duodenum is the first part of the small intestine which we are going to get a better view when I show you the pancreas slide.2975

    If it was not for that common bile duct you would not be getting bile into the small intestine.2983

    Bile is made from a lot of resources.2990

    One of the sources is cholesterol.2994

    It contains things like bile salts and the bile in general like I said earlier emulsifies fats.2996

    The emulsification of fats is a fancy term for breaking down lipids into smaller bits that make it easier for enzymes to further break them down 3004

    into tiny chemical bits for absorption into the small intestine.3021

    Bile helps break down fats big time.3025

    You got to get a lot of bile in the duodenum.3029

    You produce something like a liter of bile per day on average and that bile can creep up in the stomach because duodenum is right next to it.3031

    Bile can also be found further down the line in the small intestine.3040

    Bile can also be reabsorbed from the intestines and it can actually go back to the liver and can be recycled throughout the day.3046

    Some people do get their gallbladder removal and I will talk more about gallstones.3056

    The reason why you do not need a gallbladder is as long as the common hepatic duct is still connected through the bile duct that takes the duodenum, 3061

    you do not need that temporary holding sac for the bile.3074

    I know people who have had their gall bladder removed but their liver still producing it and still sending it down at the small intestine.3079

    The pancreas this is an endocrine organ has a lot to do with hormones but it also is a definite part of the digestive system.3086

    It lies posterior just behind stomach in between the duodenum and the spleen which is a lymphatic organ and part of the immune system.3095

    It is about 15cm long, pinkish grey, and it is got a body and a tail.3104

    Here is the body of the pancreas.3109

    The tail is that tapered part that is closer to the left side of your body.3111

    You can see here is the duodenum, the beginning of the small intestine.3117

    Your spleen would be right over here.3120

    It produces digestive enzymes and buffers.3123

    Here are some examples of the enzymes that are produce and sent out to the pancreatic duct.3126

    You can see that this connects to the duodenum just like the bile duct connects to the duodenum.3132

    Pancreatic alpha amylase this is very similar to salivary amylase in your saliva.3140

    This helps breakdown sugars.3145

    Pancreatic lipids the fact that helps break down fats.3147

    Nuclease are enzymes that breakdown DNA and RNA because when you are consuming plants or animal products they have DNA and RNA too.3151

    The perioditic enzyme also known as protease that is one of the main kinds of these enzymes.3160

    They help breakdown proteins.3165

    Some digestive conditions and disorders.3168

    Gastritis is an irritation or infection of the stomach.3173

    It is curable.3178

    Antibiotics can help with that.3179

    Ulcers do not just happen in the stomach.3182

    They can happen in various parts of the digestive tract.3187

    It is a wearing away of the lining and it can be very painful and there can be even some internal bleeding.3190

    There was this myth years ago that stress cause ulcers.3196

    Stress can lower the effectiveness of your immune system and that can make an ulcer more likely to happen.3202

    But it is not a direct cause.3211

    There are actually a kind of bacterium that has been linked to the causing of ulcers.3212

    It is pilori, I will later on about the specific name of it.3218

    There is a kind of bacterium that is the root of causing ulcers.3229

    Antibiotics can get rid of it.3234

    H pilori causes ulcers.3236

    Gallstones, if there is inability of getting bile salts out of the gallbladder and into the small intestine effectively you get this back up 3249

    and the build up of bile pile salts leads to the formation of stones.3261

    This is a gallbladder that has been taken in a person’s body, you can see they are literally stones.3266

    Hard deposits that are caused this back up.3271

    This person is still able to get bile out of their liver to the small intestine but this needed to be removed.3276

    The back up inability of bile to go from liver to the small intestine can be a problem.3282

    Cholera is an infection that causes massive diarrhea and massive fluid loss.3289

    This in the past killed much more people because the discovery of antibiotics and getting rid of the bacteria that can cause cholera has saved many lives.3296

    But cholera if untreated can dehydrate a person so much that it kills them.3308

    Hepatitis is an infection of the liver.3313

    Hepatitis A, B, C, D, or E.3316

    A is the least harmful type typically.3319

    Hepatitis in general is infections of the liver can be deadly because the liver is an organ that is very important.3323

    Jaundice is the inability of the liver to regulate the amount of bilirubin in the bloodstream can lead to jaundice.3330

    When this bilirubin molecule is throughout the body way too much, the buildup of it in the skin and even eyes causes this yellowish kind of appearance.3342

    You can see from this particular image, this guy his sclera are even yellow, the whites in his eyes.3352

    Depending on your skin tone the yellowish of the skin is going to be more apparent.3361

    I found that my aunt who was a nurse in a neonatal unit in the hospital said that babies who have jaundice right after they are born, 3367

    they found that if they put on heat lamps on them that actually can help get rid of jaundice fairly quickly.3378

    Jaundice is something that is curable but the yellowness is not very pleasant.3387

    Cirrhosis is liver disease that is a liver that has been damaged overtime by too many toxins, drug abuse, alcohol abuse overtime causes cirrhosis.3394

    If you do not get liver transplant cirrhosis is deadly.3408

    Constipation is having feces that are just way too solid and too rough.3411

    That backup and solid balls of fecal matter causes a backup and it is hard to physically push it out.3417

    Like I have mentioned earlier with hemorrhoids, getting more fiber, more plant material in your diet, whole grains, more water in your diet,3427

    and lessening the amount of meat intake can help a lot with constipation.3436

    Diarrhea like I have mentioned with large intestine before is a virus or bacterium that has inhibited your large intestines ability to reabsorb water.3441

    That excess water in your fecal matter is going to cause diarrhea.3452

    Lactose intolerance, there are genetic links to lactose intolerance where the amount of lactase, the enzyme that breaks down lactose 3456

    and dairy products is just not as high in certain people as in others.3466

    I have no problem digesting lactose.3470

    I can eat a lot of cheese, or ice cream and I feel fine.3473

    I do not notice any negative effects when I go to the bathroom.3476

    Some people do.3479

    Some people it just takes a little bit of cheese, ice cream, or milk and may have that uncomfortable sensation in their GI tract and then may notice trouble on the toilet.3480

    There are medications that can assist your body's ability to break down lactose.3494

    There are pills that you can take to help with lactose intolerance.3499

    Gingivitis or gum disease known as gingivitis is a gum infection.3504

    The gingiva is a technical term for your gums.3510

    Not brushing your teeth adequately, not flossing can lead to gingivitis.3513

    Periodontal disease is another example of a disease that is going to impact your teeth and you are more likely to lose your teeth if that is not treated.3519

    Brushing your teeth twice a day and using floss is going to minimize the chances of getting gingivitis.3528

    You do not want to get that.3534

    It is going to give you bad breath and very unattractive appearance in terms of your oral health.3535

    This is actually from what I have heard the most common bacterial infection on planet earth.3542

    Because if you look at populations around the globe, various people are not keeping their mouth as clean as they could.3548

    They may not have access to a toothbrush or toothpaste or dental care.3556

    Gingivitis is a very common mouth infection and very common bacterial infection in general.3560

    Thank you for watching