How do oxygen and carbon dioxide move in the lungs?

How do oxygen and carbon dioxide move in the lungs?

• A. Oxygen moves from blood to alveoli; carbon dioxide moves from alveoli to blood.
• B. Both move fromalveoli to blood.
• C. Oxygen moves from alveoli to blood; carbon dioxide moves from blood to alveoli.
• D. Both move from blood to alveoli.

Answer: (C)

Gas exchange in the lungs happens by diffusion across the thin respiratory membrane, driven by partial pressure gradients. Oxygen moves from the alveolar air, where its partial pressure is high, into the blood in the pulmonary capillaries, where its partial pressure is lower. Carbon dioxide moves in the opposite direction: its partial pressure is higher in the blood arriving from the tissues than in the alveolar air, so it diffuses from blood into the alveoli to be exhaled. This setup allows oxygen to enter the bloodstream for delivery to tissues while carbon dioxide, a waste product, is removed via exhalation. The other directions would require the partial pressures to be reversed, which is not the case at the lungs.

Gas exchange in the lungs happens by diffusion across the thin respiratory membrane, driven by partial pressure gradients. Oxygen moves from the alveolar air, where its partial pressure is high, into the blood in the pulmonary capillaries, where its partial pressure is lower. Carbon dioxide moves in the opposite direction: its partial pressure is higher in the blood arriving from the tissues than in the alveolar air, so it diffuses from blood into the alveoli to be exhaled. This setup allows oxygen to enter the bloodstream for delivery to tissues while carbon dioxide, a waste product, is removed via exhalation. The other directions would require the partial pressures to be reversed, which is not the case at the lungs.