What is the main function of alveoli in the lungs?

The main function of alveoli in the lungs is oxygen exchange. Alveoli are tiny, balloon-like structures at the end of the respiratory tree, specifically designed to facilitate the transfer of gases between the air and the bloodstream. They provide a large surface area, which is critical for efficient gas exchange. When oxygen-rich air reaches the alveoli, oxygen diffuses through the thin walls of the alveoli into the surrounding capillaries, where it enters the bloodstream. Simultaneously, carbon dioxide, which is a waste product of metabolism, diffuses from the blood into the alveoli to be exhaled. This exchange process is essential for maintaining proper levels of oxygen in the body and removing carbon dioxide, thus playing a crucial role in respiration and overall metabolic function.

The other functions listed, such as carbon dioxide removal and airway humidification, are part of the respiratory process but do not specifically highlight the unique role of alveoli, whereas the exchange of oxygen is their primary function.