What is the primary function of alveoli in the lungs?

The primary function of alveoli in the lungs is to facilitate gas exchange between the air in the lungs and the blood. Alveoli are tiny, balloon-like structures that are clustered at the end of the bronchioles. Their walls are extremely thin and are surrounded by a network of capillaries, which allows for the efficient transfer of oxygen into the blood and carbon dioxide out of the blood.

While increasing surface area for diffusion is a significant aspect of their role—since the large number of alveoli creates an extensive surface area to optimize gas exchange—their main purpose is to allow oxygen and carbon dioxide to move between the alveoli and the bloodstream. This gas exchange process is crucial for respiration and is the reason why the alveoli play such an essential role in pulmonary function.

In the context of the other options, oxygen storage does not accurately reflect the function of alveoli, as they do not store oxygen; rather, they facilitate its transfer. Air filtration is primarily the responsibility of the upper respiratory tract, which traps particulates before they reach the alveoli. Therefore, while increasing the surface area contributes to their efficiency, the essential role of alveoli is primarily centered on gas exchange, making that the most accurate response.