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bronchi - The diaphragm is a layer of muscle which is...

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- bronchi, bronchioles, alveoli - To conduct, moisturize, and warm inhaled air and, by bronchiolar sphincters, to regulate the passage of air into the alveoli. Bronchi enter the right and left lungs, breaking up as they do so into smaller bronchi and bronchioles and ending in small air sacs or alveoli, where gaseous exchange occurs . The structure of the alveoli facilitates their function. • They are moist which increases the rate of diffusion of gases. • They are highly vascularized which allows more exchange of gases. • The thin walls of the alveoli allow materials to be exchanged quickly and easily. • A layer of lipoprotein reduces surface tension and prevents the alveoli from collapsing. • They are small and number in the millions. This increases their surface area and allows for speedy gas exchange. • Stretch receptors in their walls signal medulla oblongata to stop inhalation. - diaphragm and ribs -
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Unformatted text preview: The diaphragm is a layer of muscle which is convex above, domed, and squashed in the centre by the heart. When it contracts it flattens and increases the space above it to assist in bringing in and expelling air from the lungs. The ribs are elevated as we inhale to further expand the volume of the cavity and assist in bringing in air. • pleural membranes - Like most internal organs, each lung is enclosed in a double-layered sac the pleural membranes. Between the inner and outer membranes is a space in which the pressure is less than atmospheric (less by 5-10 atm.); this is what is often referred to as "negative pressure". • thoracic cavity - As the thorax expands during inspiration (ribs raised, diaphragm lowered), the pleural space expands and the sub-atmospheric pressure is further decreased; this assists in drawing air into the lungs. The reverse takes place during exhalation....
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