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Alveoli

By Terry Martin, About.com

Updated: May 28, 2006

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

Definition:
Alveoli are tiny, delicate air sacs deep within the lungs. Normal, healthy lungs look like upside down branches of a tree, with many thousands of these tiny air sacs at the ends of those branches. It is at this level that the gas/blood exchange occurs, allowing oxygen from the air to enter the bloodstream and CO2 to leave it.

Toxins from cigarette smoke break the thin walls of alveoli, leaving larger, less efficient air sacs. In a smoker, this process often signals the beginning of chronic lung disease, such as chronic bronchitis and emphysema.

See also:

All About COPD
Emphysema Causes and Symptoms
Also Known As: air sacs

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