What is the primary role of alveoli in the respiratory system?

The primary role of alveoli in the respiratory system is gas exchange. These tiny, balloon-like structures are located at the end of the respiratory tree and are surrounded by a network of capillaries. When you inhale, oxygen from the air enters the alveoli and diffuses across their thin walls into the bloodstream. This oxygen is then transported to the body's cells for use in respiration. At the same time, carbon dioxide, a waste product of cellular respiration, travels from the blood into the alveoli to be exhaled. This process is crucial for maintaining the body's oxygen levels and removing carbon dioxide, making alveoli essential for effective respiration and overall metabolic function.

The other options focus on functions that are not performed by alveoli, such as filtering air, which is primarily a role of the nasal passages and larger airways; producing sound, which involves the vocal cords located in the larynx; and regulating blood flow, which is a function of the cardiovascular system rather than the respiratory system.