In the respiratory system, what is the primary site of gas exchange?

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

Answer: (C)

The primary site of gas exchange in the respiratory system is the alveoli. These tiny, balloon-like structures are located at the end of the bronchioles and are crucial for the exchange of oxygen and carbon dioxide between the air and the blood. The walls of the alveoli are extremely thin and are lined with a rich network of capillaries, which facilitates the diffusion of gases.

When air enters the lungs, it reaches the alveoli, where oxygen from the inhaled air passes through the alveolar walls into the blood, and carbon dioxide from the blood diffuses into the alveoli to be exhaled. This effective exchange process is essential for maintaining proper oxygen levels in the body and removing carbon dioxide, a waste product of metabolism.

In contrast, structures like the bronchi and trachea are primarily pathways for air to travel into the lungs and do not participate in gas exchange. The diaphragm is a muscle that plays a critical role in inhalation and exhalation but is not directly involved in the exchange of gases. Thus, the alveoli are uniquely adapted for this vital function, making them the primary site of gas exchange in the respiratory system.