What physiological process primarily takes place in the alveoli?

The primary physiological process that occurs in the alveoli is gas exchange. The alveoli are tiny air sacs located in the lungs where oxygen from inhaled air diffuses across the alveolar membrane into the bloodstream, while carbon dioxide, a waste product from metabolism, diffuses in the opposite direction—from the blood into the alveoli to be exhaled. This exchange is crucial for maintaining proper oxygen levels in the body and removing carbon dioxide, a process vital for cellular respiration and overall metabolic function.

The structure of the alveoli, being highly vascularized and featuring a large surface area, facilitates this efficient gas exchange. The thin walls of the alveoli allow for swift diffusion of gases, making them essential for respiratory physiology. The other options describe functions that do not occur within the alveoli, highlighting the specialized role of these structures in the respiratory system.