What function do alveoli serve in the respiratory system?

Alveoli are small, balloon-like structures located at the end of the respiratory tree in the lungs, and their primary function is to facilitate gas exchange. They provide a vast surface area where oxygen from inhaled air can diffuse into the blood while allowing carbon dioxide in the blood to be expelled into the air. This process is essential for maintaining the oxygen levels in the bloodstream and removing carbon dioxide, a waste product of metabolism.

The structure of the alveoli, featuring thin walls and a rich blood supply from surrounding capillaries, optimizes this exchange process, making it more efficient. This unique design enables the lungs to effectively manage the respiratory needs of the body, ensuring that oxygen is delivered to tissues and organs while carbon dioxide is removed efficiently.

Other options describe functions that are related to the respiratory process but do not specifically highlight the primary role of the alveoli in gas exchange. For instance, filtering impurities, warming air, and delivering oxygen are actions that are part of the broader respiratory system but do not occur directly within the alveoli themselves. The actual gas exchange happens primarily in these tiny sacs, making their role crucial in the respiratory system.