What is the term for the air sacs where gas exchange occurs?

The term for the air sacs where gas exchange occurs is alveoli. Alveoli are small, balloon-like structures located at the ends of the respiratory bronchioles, and they are the primary sites in the lungs where oxygen is absorbed into the bloodstream and carbon dioxide is expelled. Their structure, which includes a large surface area and a thin membrane, facilitates this gas exchange process effectively.

The alveoli are surrounded by a network of capillaries, allowing efficient transfer of gases. The presence of surfactant in the alveoli helps to keep them open, reducing surface tension and preventing collapse, making them essential for proper respiratory function.

In contrast, bronchi and bronchioles are part of the airway leading to the alveoli—they serve to conduct air but are not directly involved in gas exchange. Respiratory bronchioles are the transitional passageways that lead to the alveoli but do not perform the gas exchange themselves. Thus, alveoli are specifically designated as the air sacs responsible for this crucial function in the respiratory system.