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Alveoli

By Terry Martin, About.com

Updated January 13, 2009

About.com Health's Disease and Condition content is reviewed by our Medical Review Board

Illustration © A.D.A.M.
Definition:
Tiny, delicate air sacs deep within the lungs, where the gas/blood exchange occurs. Oxygen from inhaled air passes through the walls of aveoli and enters the bloodstream while carbon dioxide passes out in the same way when air is exhaled.

Toxins from cigarette smoke can break the thin walls of alveoli, leaving larger, less efficient air sacs. In a smoker, this process signals the beginning of emphysema, a form of COPD.

See also:
"All About COPD"
"Emphysema Causes and Symptoms"

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