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

The microscopic sacs in the lungs where gas exchange occurs are called alveoli. These small, balloon-like structures are lined with thin cell membranes that facilitate the exchange of oxygen and carbon dioxide between the air within the lungs and the blood in the surrounding capillaries. This process is crucial for maintaining proper oxygen levels in the blood and removing carbon dioxide, which is a waste product of metabolism.

Alveoli have a large surface area due to their numerous quantity, effectively allowing for a significant amount of gas exchange to take place. The presence of the thin membranes ensures that gases can diffuse easily; oxygen moves from the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli to be exhaled.

In contrast, bronchi are the larger air passages that lead from the trachea to the lungs, facilitating airflow but not being directly involved in gas exchange. Capillaries are tiny blood vessels that surround the alveoli, playing a critical role in the transport of gases but not serving as the site of gas exchange itself. Arteries are blood vessels that carry blood away from the heart and do not participate directly in the gas exchange process within the lungs.