Which factor increases alveolar gas absorption?

Which factor increases alveolar gas absorption?

• A. Decreasing partial pressure difference
• B. Increasing partial pressure difference
• C. Lower diffusion rate
• D. Lower ventilation rate

Answer: (B)

The amount of gas absorbed from the alveoli into the blood is driven by the partial pressure gradient between the alveolar gas and the blood across the alveolar–capillary membrane. When this gradient is larger, the driving force for diffusion is stronger, so more gas moves per unit time into the blood. This is the essence of diffusion across membranes: rate increases with a bigger driving force. In the lungs, oxygen moves from the alveoli (higher partial pressure) into the blood (lower partial pressure), and carbon dioxide moves in the opposite direction. Raising the partial pressure difference between the two compartments speeds up this transfer, up to physiological limits. Conversely, decreasing the partial pressure difference reduces the driving force and slows absorption. A lower diffusion rate means less gas crosses per unit time, and a lower ventilation rate can diminish the fresh gas available in the alveoli, which tends to reduce the gradient and thus the absorption rate.

The amount of gas absorbed from the alveoli into the blood is driven by the partial pressure gradient between the alveolar gas and the blood across the alveolar–capillary membrane. When this gradient is larger, the driving force for diffusion is stronger, so more gas moves per unit time into the blood. This is the essence of diffusion across membranes: rate increases with a bigger driving force.

In the lungs, oxygen moves from the alveoli (higher partial pressure) into the blood (lower partial pressure), and carbon dioxide moves in the opposite direction. Raising the partial pressure difference between the two compartments speeds up this transfer, up to physiological limits.

Conversely, decreasing the partial pressure difference reduces the driving force and slows absorption. A lower diffusion rate means less gas crosses per unit time, and a lower ventilation rate can diminish the fresh gas available in the alveoli, which tends to reduce the gradient and thus the absorption rate.