Which structure is the primary site for gas exchange in the lungs?

The primary site for gas exchange in the lungs is the alveoli. These tiny, balloon-like structures are located at the end of the respiratory branches and significantly increase the surface area available for the exchange of gases. The alveoli are surrounded by a network of capillaries, which facilitates the transfer of oxygen and carbon dioxide between the air in the alveoli and the blood.

Oxygen from the inhaled air diffuses across the thin walls of the alveoli into the capillary blood, where it binds to hemoglobin in red blood cells. Simultaneously, carbon dioxide, which is a waste product of metabolism in the blood, diffuses from the capillaries into the alveoli to be exhaled. This efficient gas exchange is crucial for maintaining proper oxygen levels in the blood and removing carbon dioxide from the body, which supports cellular respiration and overall metabolic processes.

The other structures listed—bronchi, trachea, and capillaries—play important roles in the respiratory system but are not the primary sites of gas exchange. The bronchi serve as passageways for air to enter and exit the lungs, while the trachea is the main airway conducting air to the bronchi. Although capillaries are essential for facilitating gas