What drives gas exchange at the alveolocapillary membrane?

• A. Temperature gradients
• B. Pressure gradients
• C. Concentration gradients
• D. Diffusion rates

Answer: (B)

Gas exchange at the alveolocapillary membrane is primarily driven by pressure gradients. In the alveoli, oxygen and carbon dioxide are exchanged between the air in the alveoli and the blood in the capillaries. The partial pressure of oxygen in the alveoli is higher than in the venous blood entering the capillaries, which facilitates the movement of oxygen from the alveoli into the blood. Conversely, the partial pressure of carbon dioxide is higher in the blood than in the alveolar air, causing carbon dioxide to diffuse from the blood into the alveoli for exhalation.

This process is essential for maintaining proper oxygenation of blood and the elimination of carbon dioxide, which is a waste product of metabolism. The efficiency of gas exchange depends largely on the differences in partial pressures, making pressure gradients the key factor driving diffusion across the membrane.

While temperature gradients can influence gas solubility and diffusion rates, they are not the primary drivers of the gas exchange process at this site. Concentration gradients are related to pressure gradients, as they are a factor in the driving forces of diffusion, but the established pressure differences are what allow for effective gas exchange. Although diffusion rates could contribute to how quickly the gases move, they rely on the presence of