What is the primary role of the alveoli in respiration?

The primary role of the alveoli in respiration is to facilitate the exchange of gases between the lungs and the blood. Alveoli are tiny air sacs located at the end of the respiratory bronchioles, and they provide a large surface area for gas exchange due to their extensive network and thin walls. When air reaches the alveoli, oxygen from the inhaled air passes through the alveolar walls into the surrounding capillaries, where it enters the bloodstream. Simultaneously, carbon dioxide from the blood passes into the alveoli to be exhaled. This process is essential for maintaining the body's oxygen supply and removing carbon dioxide, a waste product of metabolism.

Other options present related functions, but they do not represent the primary role of the alveoli in the respiratory process. For example, while the production of surfactant is important for lung function and helping prevent alveolar collapse, it is not the primary function of the alveoli. Additionally, filtering impurities from the air and regulating gas pressure are functions more related to the upper respiratory system and other physiological mechanisms, rather than the alveoli themselves.