Which structure is responsible for gas exchange between air and blood?

Which structure is responsible for gas exchange between air and blood?

• A. Alveolar sac
• B. Primary bronchi
• C. Tertiary bronchi
• D. Alveoli

Answer: (D)

The alveoli are the primary structures responsible for gas exchange between air and blood in the respiratory system. These tiny, balloon-like structures are located at the end of the bronchioles and provide a large surface area to facilitate the diffusion of oxygen and carbon dioxide. The walls of the alveoli are extremely thin and are lined with capillaries, allowing oxygen to pass from the air within the alveoli into the blood, while carbon dioxide moves from the blood into the alveoli to be exhaled.

The alveolar sacs, while closely related and sometimes included in discussions about gas exchange, refer to the clusters of alveoli that resemble bunches of grapes. They play a supportive role in the exchange process but are not the primary sites for gas transfer themselves.

The primary bronchi and tertiary bronchi are part of the conducting zone of the respiratory system, responsible for transporting air to the lungs. They do not participate in gas exchange, as they lack the necessary surface area and thin membranes that characterize the alveoli. Their primary function is to ensure air reaches the alveoli, where the actual exchange occurs.