What are the microscopic sacs in the lungs where gas exchange occurs called?

The microscopic sacs in the lungs where gas exchange occurs are called alveoli. Alveoli are tiny, balloon-like structures at the end of the respiratory tree and are crucial in the respiratory process. When air is inhaled, it enters the alveoli, where oxygen from the air diffuses across the thin walls of the alveoli into the surrounding capillaries. At the same time, carbon dioxide in the blood moves from the capillaries into the alveoli to be exhaled. This exchange of gases is vital for maintaining the oxygen and carbon dioxide balance in the body and is fundamentally how oxygen is delivered to tissues and organs.

Other structures mentioned, like bronchi, bronchioles, and capillaries, play important roles in respiration, but they do not function specifically as the sites of gas exchange. The bronchi and bronchioles are involved in conducting air into the lungs, while capillaries are blood vessels that surround the alveoli where the exchange of gases actually takes place. However, the alveoli themselves are where this critical exchange specifically occurs.