What surrounds each alveolus for gas exchange?

The correct answer emphasizes the role of capillaries in the process of gas exchange within the lungs. Each alveolus, which is a small air sac in the lungs, is surrounded by a network of capillaries. These capillaries are tiny blood vessels that facilitate the transfer of oxygen and carbon dioxide between the air in the alveoli and the blood.

During inhalation, oxygen-rich air enters the alveoli, and oxygen molecules diffuse across the thin walls of the alveoli and into the bloodstream through the surrounding capillaries. Simultaneously, carbon dioxide, which is a waste product of metabolism, moves from the blood in the capillaries into the alveoli to be exhaled. This efficient arrangement is crucial for maintaining proper oxygen levels in the blood and removing carbon dioxide effectively.

Understanding this relationship between alveoli and capillaries highlights the importance of the circulatory system in respiratory function and demonstrates how these systems work together to support life.