Which term describes diffusion: exchange of oxygen and carbon dioxide between the alveoli and circulating blood?

Which term describes diffusion: exchange of oxygen and carbon dioxide between the alveoli and circulating blood?

• A. Diffusion
• B. Perfusion
• C. Ventilation
• D. Eupnea

Answer: (A)

Diffusion is the movement of gas molecules from an area of higher partial pressure to an area of lower partial pressure across a membrane. In the lungs, oxygen is at a higher partial pressure in the alveolar air than in the blood, so it diffuses into the capillary blood. Carbon dioxide is higher in the blood than in the alveolar air, so it diffuses from the blood into the alveoli to be expelled. This gas exchange across the alveolar-capillary membrane is diffusion. Perfusion refers to blood flow through the lungs and is needed for gas exchange but is not the exchange process itself. Ventilation is the movement of air into and out of the lungs, and eupnea means normal breathing. So diffusion specifically describes the actual exchange of O2 and CO2 between alveoli and blood.

Diffusion is the movement of gas molecules from an area of higher partial pressure to an area of lower partial pressure across a membrane. In the lungs, oxygen is at a higher partial pressure in the alveolar air than in the blood, so it diffuses into the capillary blood. Carbon dioxide is higher in the blood than in the alveolar air, so it diffuses from the blood into the alveoli to be expelled. This gas exchange across the alveolar-capillary membrane is diffusion. Perfusion refers to blood flow through the lungs and is needed for gas exchange but is not the exchange process itself. Ventilation is the movement of air into and out of the lungs, and eupnea means normal breathing. So diffusion specifically describes the actual exchange of O2 and CO2 between alveoli and blood.