What are alveoli used for?

Function

The alveoli serve to increase the surface area of the lungs for the efficient exchange of gases between the lungs and the blood. The air inside the alveoli contains oxygen, while the blood flowing in the capillaries contains carbon dioxide. Oxygen from the air diffuses across the thin walls of the alveoli and capillaries and into the bloodstream, while carbon dioxide diffuses out of the bloodstream into the air inside the alveoli. This exchange of gases is essential for life.