What factor primarily determines the rate of diffusion of gases across the respiratory membrane?

The primary factor that determines the rate of diffusion of gases across the respiratory membrane is the partial pressure of the gases involved. In the context of respiration, gases will move from an area of higher partial pressure to an area of lower partial pressure. This process is driven by the concentration difference of gases, which is directly related to their partial pressures.

In the lungs, oxygen moves from the alveoli, where its partial pressure is relatively high, into the blood in the pulmonary capillaries, where its partial pressure is lower. Conversely, carbon dioxide moves from the blood, where its partial pressure is higher, into the alveoli to be expelled from the body, where its partial pressure is lower. This difference in partial pressures creates a gradient that facilitates diffusion, making it the most significant determinant in this process.

While temperature, concentration of proteins, and volume of air can influence gas exchange in various indirect ways, they do not have the overarching impact on diffusion rates compared to the gradients established by partial pressures of the gases involved.