Which vessels are primarily responsible for gas exchange in the lungs and tissues?

Which vessels are primarily responsible for gas exchange in the lungs and tissues?

• A. Capillaries
• B. Arteries
• C. Veins
• D. Arterioles

Answer: (A)

Gas exchange happens where blood is in very close contact with air or tissue cells, across walls that are extremely thin. Capillaries form the vast, fine network around each alveolus in the lungs and around every body cell, and their walls are only one cell thick. This setup allows oxygen to diffuse from the alveolar air into the blood and carbon dioxide to diffuse in the opposite direction in the lungs. In tissues, capillaries place blood right next to cells, so oxygen can diffuse out of the blood into cells to support metabolism, while carbon dioxide produced by those cells diffuses into the blood to be carried away. Arteries and arterioles mainly deliver blood to sites of exchange, and veins collect blood to return to the heart, but the actual transfer of gases occurs across capillary walls. So capillaries are the primary sites of gas exchange.

Gas exchange happens where blood is in very close contact with air or tissue cells, across walls that are extremely thin. Capillaries form the vast, fine network around each alveolus in the lungs and around every body cell, and their walls are only one cell thick. This setup allows oxygen to diffuse from the alveolar air into the blood and carbon dioxide to diffuse in the opposite direction in the lungs. In tissues, capillaries place blood right next to cells, so oxygen can diffuse out of the blood into cells to support metabolism, while carbon dioxide produced by those cells diffuses into the blood to be carried away. Arteries and arterioles mainly deliver blood to sites of exchange, and veins collect blood to return to the heart, but the actual transfer of gases occurs across capillary walls. So capillaries are the primary sites of gas exchange.