In the lungs, the tiny sacs where gas exchange occurs are called what?

In the lungs, the tiny sacs where gas exchange occurs are called what?

• A. Bronchi
• B. Alveoli
• C. Pleura
• D. Trachea

Answer: (B)

Gas exchange occurs in tiny sacs called alveoli. These are at the ends of the airways and are surrounded by a dense network of capillaries; their walls are extremely thin and coated with a thin liquid film that contains surfactant to prevent collapse. This combination gives a very large surface area for diffusion, allowing oxygen to move from the air into the blood and carbon dioxide to move from the blood into the air to be exhaled. The other structures have different roles: bronchi are the larger airways that conduct air into the lungs, the trachea is the main windpipe, and the pleura is the membrane surrounding the lungs, not a site of gas exchange.

Gas exchange occurs in tiny sacs called alveoli. These are at the ends of the airways and are surrounded by a dense network of capillaries; their walls are extremely thin and coated with a thin liquid film that contains surfactant to prevent collapse. This combination gives a very large surface area for diffusion, allowing oxygen to move from the air into the blood and carbon dioxide to move from the blood into the air to be exhaled. The other structures have different roles: bronchi are the larger airways that conduct air into the lungs, the trachea is the main windpipe, and the pleura is the membrane surrounding the lungs, not a site of gas exchange.