What role do the alveoli play in the respiratory system?

The alveoli are tiny, balloon-like structures located at the end of the bronchial tubes in the lungs, and they play a crucial role in the respiratory system primarily by facilitating gas exchange with the capillaries. Each alveolus is surrounded by a network of capillaries that transport blood. When you breathe in, oxygen from the air fills the alveoli and diffuses across the thin walls of the alveoli into the blood in the capillaries. At the same time, carbon dioxide from the blood diffuses out of the capillaries and into the alveoli to be exhaled. This efficient exchange of gases is essential for maintaining proper levels of oxygen and carbon dioxide in the body, supporting cellular function and metabolism.

Regarding the other options, storing oxygen for later use is not a function of the alveoli, as they are designed specifically for gas exchange rather than storage. While the respiratory system does have some mechanisms to filter impurities, this is primarily the role of the nasal passages and larger airway structures, not the alveoli themselves. Lastly, the alveoli are not responsible for protecting the lungs from infection; that role is typically fulfilled by the immune system and other structures in the respiratory tract, such as mucus and cilia.