Table of Contents
Definition and Function of Alveolus
Alveolusia is a tiny, thin-walled sac, grouped in clusters at the ends of the smallest airways (bronchioles) deep inside the lungs, that is the terminus for each breath of air. A dense mesh of capillaries entwines each alveolus. Oxygen from the air within the alveolus passes across the alveolar membrane to enter the bloodstream, while carbon dioxide and other waste gases pass across the membrane from the blood to the air within alveolus.
The clustered formations of the alveoli greatly increase the surface area for oxygen-carbon dioxide exchange. Each lung contains about 300 million alveoli, which, if spread out, would coat the surface of a tennis court-about 290 square feet.
The large surface area is important but so is the very thin interface between the airway and the blood vessel. Many disease states cause this barrier to thicken or distort, which impedes the exchange of oxygen and carbon dioxide (called decreased diffusing capacity).
For further discussion of the alveolus within the context of pulmonary structure and function please see the overview section “The Pulmonary System.”
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