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NCI Dictionary of Cancer Terms


alveoli  listen  (al-VEE-oh-ly)

  Tiny air sacs at the end of the bronchioles (tiny branches of air tubes) in the lungs. The alveoli are where the lungs and the bloodstream exchange carbon dioxide and oxygen. Carbon dioxide in the blood passes into the lungs through the alveoli. Oxygen in the lungs passes through the alveoli into the blood.

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Respiratory anatomy; drawing shows right lung with upper, middle, and lower lobes; left lung with upper and lower lobes; and the trachea, bronchi, lymph nodes, and diaphragm. Inset shows bronchioles, alveoli, artery, and vein.