What are the tiny air sacs of the lungs called where oxygen and carbon dioxide are exchanged?

The tiny air sacs of the lungs are called alveoli, which are essential for the process of gas exchange. These small, balloon-like structures provide a large surface area for oxygen to diffuse into the blood and for carbon dioxide to diffuse out of the blood. Each alveolus is surrounded by a network of capillaries, which are tiny blood vessels where this gas exchange occurs.

Alveoli are specifically designed for this function, with very thin walls that allow for efficient transfer of gases. When air reaches the alveoli, oxygen enters the bloodstream through the thin walls into the capillaries, while carbon dioxide moves from the blood into the alveoli to be exhaled. This mechanism is critical for respiration and maintaining the body's oxygen levels while removing carbon dioxide, a waste product of metabolism. The other options relate to different parts of the respiratory and circulatory systems but do not perform the gas exchange function like the alveoli do.