In diffusion limited gas exchange, what typically happens to the concentration gradients?

• A. They remain constant
• B. They equalize quickly
• C. They diminish slowly
• D. They remain steep

Answer: (D)

In diffusion limited gas exchange, the key feature is that the gas transfer depends heavily on the partial pressures or concentration gradients of the gases involved, typically oxygen or carbon dioxide, across the alveolar membranes. In this scenario, the concentration gradients remain steep. This steep gradient is essential because it drives the diffusion process; gas will continue to move from areas of higher concentration (in the alveoli) to areas of lower concentration (in the blood).

When gas exchange is diffusion-limited, the rate of gas diffusion is not simply determined by blood flow or ventilation but rather by how quickly gas can move across the alveolar-capillary membrane, which is influenced by these gradients. If the gradients were to equalize quickly or diminish significantly, the driving force for diffusion would be reduced, leading to inadequate gas exchange. Therefore, steep concentration gradients are crucial for maintaining efficient gas transfer under diffusion-limited conditions.