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Unformatted text preview: and small openings. Lung breathing probably evolved about 400 million years ago. Lungs are not entirely the sole property of vertebrates, some terrestrial snails have a gas exchange structures similar to those in frogs. Respiratory System Principles 1. Movement of an oxygen-containing medium so it contacts a moist membrane overlying blood vessels. 2. Diffusion of oxygen from the medium into the blood. 3. Transport of oxygen to the tissues and cells of the body. 4. Diffusion of oxygen from the blood into cells. 5. Carbon dioxide follows a reverse path....
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- Fall '10