Gas exchange occurs in animals via respiration. Respiratory surfaces can include skin, gills, and lungs, all of which are thin, moist, and have a large surface area due branching and folding. Insects do not use a circulatory system as an intermediate for gas exchange. Gas is exchanged directly from the epithelial surfaces at the end of the tracheoles to cells. Human respiratory structures begin with a nasal cavity, pharynx, larynx, and epiglottis. Air then moves down the trachea and left and right bronchi, into the bronchioles, and to the alveoli sacs where gas exchange occurs. Hemomglobin then transport oxygen through the blood. Ventilation, the intake of air, occurs through inspiration and expiration via the diaphragm, thorax, or abdomen and is modulated in humans by the medulla in the brain.
Respiration is the process
through which gas exchange occurs. During respiration, animals take
in oxygen and release carbon dioxide.
Gas exchange in simple aquatic
animals occurs via diffusion across the whole surface of the body.
In more complex aquatic animals, gills provide a surface across
which gas exchange can occur.
Some animals rely on diffusion
across the skin for gas exchange. More complex animals have internal
respiratory surfaces that include branched tubes or folded
In insects, air enters the body
through small openings called spiracles. Air then passes into air
ducts called tracheae, which branch into tracheoles that reach the
cells of the body so that gas exchange can occur.
In mammals, air enters the
nasal cavity, passes through the pharynx and larynx and then into
the trachea. Next, the air enters the bronchi, which branch into
bronchioles, ending in alveoli, the site of gas exchange.
Ventilation occurs during the
process of breathing. During inspiration, air is pulled into the
lungs by the negative pressure created when the thoracic cavity
expands. The reverse process occurs during expiration.
The Respiratory System
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The book and CD package include two full length practice exams that are presented with all questions answered and explained. The author also presents detailed reviews of all test topics and includes multiple-choice and free-response questions with answers at the end of each topic's chapter.
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