Which structure is a primary site for gas exchange?

Which structure is a primary site for gas exchange?

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

Answer: (A)

Gas exchange happens in the alveoli, the tiny air sacs at the end of the respiratory tree. They have walls that are extremely thin and are wrapped in a dense network of capillaries, giving a huge surface area for diffusion. Oxygen from the inhaled air passes through the alveolar and capillary membranes into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. The thin alveolar–capillary barrier and the presence of surfactant help make this diffusion efficient and keep the alveoli stable. The trachea, bronchi, and larynx are conducting airways that move and condition air but do not participate in gas exchange, so the alveoli are the primary site where this exchange occurs.

Gas exchange happens in the alveoli, the tiny air sacs at the end of the respiratory tree. They have walls that are extremely thin and are wrapped in a dense network of capillaries, giving a huge surface area for diffusion. Oxygen from the inhaled air passes through the alveolar and capillary membranes into the blood, while carbon dioxide moves from the blood into the alveolar air to be exhaled. The thin alveolar–capillary barrier and the presence of surfactant help make this diffusion efficient and keep the alveoli stable. The trachea, bronchi, and larynx are conducting airways that move and condition air but do not participate in gas exchange, so the alveoli are the primary site where this exchange occurs.