What occurs in an alveolus?

In an alveolus, gas exchange is the primary function. Alveoli are tiny air sacs located in the lungs where the process of exchanging oxygen and carbon dioxide takes place. When air enters the alveoli, oxygen from the air diffuses across the thin walls of the alveoli into the surrounding capillaries, which are small blood vessels. At the same time, carbon dioxide from the blood diffuses into the alveoli to be exhaled. This efficiency in gas exchange is facilitated by the large surface area and the thin barrier of the alveolar walls, allowing for rapid diffusion of gases.

The other options do not accurately describe the function of the alveoli. Air filtration occurs in the upper respiratory tract and not in the alveoli. Mucus production is a function of goblet cells found in the respiratory tract, while oxygen transport happens within the bloodstream after the gas exchange has occurred in the alveoli.