Question on Gases and Permeability Kaplan

[betterfuture]

Why does it state that visceral balloon is permeable and yet a parietal balloon is not yet in the answer choice it says that there will be an exchange of gases. Wasn't the parietal balloon impermeable? How is it allowing for the exchange of gases? I got the answer right because I guessed. Thanks!

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[aldol16]

How are the balloons being set up? Where is the pleural space relative to the balloons?

 

[betterfuture]

The setup is modeled after a human lung. There is a visceral balloon and a parietal balloon. The visceral balloon is put inside a parietal balloon.

 

[aldol16]

Okay, then it makes sense. The visceral balloon that is inside the parietal balloon is permeable. The parietal balloon that envelopes the visceral balloon is not permeable, meaning the gases can't escape into the environment. So if you put gas into the visceral balloon and another into the pleural space (space between the outside of the visceral balloon ad the inside of wall of the parietal balloon), then it would make sense that they would mix within the confines of the parietal balloon.

 

[betterfuture]

If the parietal balloon is impermeable, then wouldn't that mean that it doesn't allow exchange of gases? How does it allow exchange of gas with the visceral balloon? How is it able to do that?

 

[aldol16]

If the parietal balloon is impermeable, then wouldn't that mean that it doesn't allow exchange of gases? How does it allow exchange of gas with the visceral balloon? How is it able to do that?

Either I'm not imagining the scenario correctly or you're not imagining the scenario correctly. Based on what you told me - i.e. the visceral balloon being put inside the parietal balloon - here's what I'm imagining and I'll use an analogy to make it easier. Think of a giant concrete building with no windows or doors. The thing is like a bunker but it lets nothing in or out. That's the parietal balloon. Now, the visceral balloon is put inside the parietal balloon. So imagine that the bunker opens into a huge space when you enter. In the middle of that space is another, smaller bunker (so imagine a huge gym with an igloo at center court). The smaller bunker, in contrast to the big one, has a bunch of tiny holes in it.

Okay, so now you put O2 in the smaller bunker and CO2 into the huge open area outside the small bunker (the gym, if you will). Nothing's going on outside the larger bunker (the parietal balloon) so ignore the outside. What's going to happen?

 

[betterfuture]

So does this have anything to do with Graham's Rate of Diffusion. I would think its just simple diffusion due to the pressure gradient set up, no? Answer explained something about different rates of CO2 and O2. Rates don't really matter. Just the fact that there will be diffusion occurring.

 

[aldol16]

But there is no pressure gradient....... CO2 is more massive than O2 so it stands to reason that O2 diffuses faster.