Partial pressure and external respiration

[Owlie]

In my anatomy and physiology course, we are studying respiratory physiology. We've discussed partial pressures, basically a concentration of gas content, O2, CO2, N2, etc.

My professor has stated that the partial pressure of one gas will not affect the diffusion of another gas. However, if a container has a limit, and you need O2 to diffuse out through a membrane. The container holds 60% CO2, and 40% O2. The atmosphere around the container holds 20% O2, and 80% CO2. O2 will diffuse out to equilibrium, and CO2 in to equilibrium. Change this to where the container holds 15% O2, and 85% CO2, with the atmosphere remaining the same. O2 will not want to diffuse into the container, in stead of out.

Am I confusing this, or is my professor wrong?

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[Cuongoff]

I believe he is right in saying that the concentrations of one gas do not affect the diffusion rates of another gas. In your example, we started with 40% O2 in the container with 20% O2 outside of the container. The O2 will diffuse out to reach equilibrium. Then we changed it to 15% O2 inside the container and 20% O2 outside the container. The O2 will move into the container from the surrounding air. The concentrations of CO2 won't affect how O2 moves in either situation. Partial pressure on the other hand, http://en.wikipedia.org/wiki/Partial_pressure, one partial pressure will affect another partial pressure since they occupy the same volume contributing to the same overall pressure of the container.

Please correct me if I am wrong.

 

[Owlie]

I believe he is right in saying that the concentrations of one gas do not affect the diffusion rates of another gas. In your example, we started with 40% O2 in the container with 20% O2 outside of the container. The O2 will diffuse out to reach equilibrium. Then we changed it to 15% O2 inside the container and 20% O2 outside the container. The O2 will move into the container from the surrounding air. The concentrations of CO2 won't affect how O2 moves in either situation. Partial pressure on the other hand, http://en.wikipedia.org/wiki/Partial_pressure, one partial pressure will affect another partial pressure since they occupy the same volume contributing to the same overall pressure of the container.

Please correct me if I am wrong.

Right. And I'm assuming that the increase in CO2 is what caused the decrease in O2, because they're occupying a space at capacity. It's the change in content that indirectly altered the diffusion.