What is the role of alveoli in the respiratory system?

• A. To produce mucus
• B. To filter air entering the lungs
• C. To facilitate the gas exchange of oxygen and carbon dioxide
• D. To transport air to and from the lungs

Answer: (C)

The alveoli play a crucial role in the respiratory system by facilitating the gas exchange of oxygen and carbon dioxide. These tiny, balloon-like structures are located at the end of the bronchioles and provide a large surface area for gas exchange to occur. When air is inhaled, oxygen enters the alveoli and diffuses across their thin walls into the surrounding capillaries, where it binds to hemoglobin in red blood cells for transport to the body’s tissues. Concurrently, carbon dioxide, which is a waste product produced by cellular metabolism, diffuses from the blood into the alveoli to be exhaled.

The structure of the alveoli is specifically adapted for this process; they have very thin walls and are surrounded by a dense network of capillaries, allowing for efficient diffusion. Additionally, the large number of alveoli in the lungs dramatically increases the surface area available for gas exchange, which is vital for meeting the oxygen demands of the body and removing carbon dioxide.

The other options do not accurately reflect the primary function of alveoli: producing mucus is a role of goblet cells and mucus-secreting glands in the respiratory tract; filtering air is primarily done by the nasal passages and larger airways; transporting air involves the trache