Air Movement and Partial Pressure

by Jason Amores Sumpter
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When we inhale and exhale Not all of the air we bring in actually participates in gas exchange on Lee the air that makes it to the Al Ville I will participate in gas exchange Some of the air we inhale will actually just sit in our trachea or bronchi and our bronchi als And we call this the dead space Really great name. You know, I often rag on scientists for how bad they're naming congee. This is a good one. This is a really good name. Now when you breathe in and out that volume of air that you inhale and exhale also has an excellent name. We call that the title volume, you know, like the like the ebb and flow of waves, right? It's like that title in and out. That's that's where that name comes from. So again, very nice kind of poetic name there. Ah, So as I'm sure you're where you know, you can breathe in and out past that title volume past that point where it's comfortable, right? You can force mawr air into your lungs. You could also force more out on your exhalations and we call that maximum volume of air where you force as much area as you can when you inhale. And as much as you can out when you exhale, that total volume is the vital capacity. Now, there's actually still Cem air that's going to remain in your in your lungs after you've forced an exhalation. And we call that remaining air the residual volume. Now, looking at our diagram here, you can see that our title volume is made up of what's going to go into the dead space and what will fill the Alvey lie. And all I really want you to know is that what fills the Alvey lie is a lot or is greater volume, uh, than what fills the dead space. Additionally, what I want you to take note of in this figure is that the air from the dead space, you know from your last breath is actually going to mix in with Theo Air that goes into the Alvey ally, and it's actually gonna be some fresh air that fills your dead space. So essentially, what I'm trying to point out here is that you're not gonna have a totally fresh air filling your Alvey lie every time you're gonna have a mix of some fresh air, this stuff here and e guess we'll call it stale air that was left over in the dead space when you exhale your last breath. And, uh, you know the point here is just that what's in your Alvey ally is not totally fresh air, and you'll see why I'm stressing this point, why it becomes important to gas exchange in a little bit. But before we get there, I also want to talk about partial pressure, which is kind of a confusing, weird idea. But it's pretty essential to understanding how gas exchange works. So the first thing to know about partial pressure is it's it's not really it's hypothetical pressure, and it's the hypothetical pressure of, you know, Let's say you take a container of air, you know from our atmosphere, and you remove all the gasses except for one. The pressure left over from that one gas that's still taking up that same volume, You know that you captured in the container. That is what we call the partial pressure, and it's the partial pressure of that particular gas. So let me give you an example. Let's say that I take a container of air from the atmosphere, I seal it off, and I remember, you know, keep it at the same temperature. But I remove all of the gas is except for nitrogen. And you can see behind my head have some pie charts that show the composition of gasses in the atmosphere. And you can see that nitrogen is the biggest part of the pie, weighing in at 78% of atmosphere composition. So if we wanted to know the partial pressure of nitrogen, what I would do is I would say, Okay, my total pressure is, you know, uhh. You know, some pressure. I'm just gonna right, like total pressure tp times the percent composition of that gas in the mixture. So in the case of nitrogen, it's 78%. So I would multiply my total pressure bye 0.78 And this would give me my partial pressure of nitrogen. Right? So the total pressure times the amount, the the percent of the composition that nitrogen takes up, which is 78%. And that gives me my partial pressure for nitrogen. I could do the same for any other gas, you know, Justus, Long as they make sure I change this number to reflect that gasses percentage in the composition. So, for example, oxygen could see here. It's like 21%. Roughly eso we could, uh, you know, find our partial pressure of oxygen by taking the total pressure and multiplying it by 0.21 So I don't actually care if you can calculate partial pressures. That's not what I want you to be able to do. I just want you to understand conceptually what the partial pressure is telling us. And the reason I want you to understand this is because people often get, um, you know, mixed up about how, uh, the composition of gasses eyes affected by altitude. Now you know, you hear people say, Oh, you know, there's less. You know there's less oxygen, higher altitude. So here's what's actually going on. The atmosphere at higher altitude has the same composition of gasses as it doesn't sea level. The composition of gas is of the atmosphere is the same regardless of altitude. What changes is the total pressure. The total pressure is higher at sea level than it is at high altitudes. And you know, you can think about it as being like gas is stacked on top of on top of you. So at sea level, there's Mawr gas stacked on top of you, right? Whereas if you're a higher altitude, there's a thinner layer of gas sitting on top of you, so there's less pressure pushing down on you. Now, uh, you know, what this means is that what's changing with altitude is the partial pressure of gas is the partial pressure of gas is, um, those partial pressures are gonna be lower at higher altitudes. The composition, the percent composition, is unchanged. Now, the reason for you know, carrying it all about partial pressures is because gas is actually defused based on partial pressures. And, uh, you know, hopefully you could have guessed this from. You know, everything we learned about diffusion and gasses will move from an area of higher partial pressure to an area of lower partial pressure. So you know that, you know, think of it as like a concentration Grady and almost right at higher partial pressure. It's like we have a higher concentration of gas there and at lower partial pressure. It's like we have a lower concentration of gas there. So are gas. Is air going to defuse from that higher partial pressure to the lower partial pressure, but that let's flip the page.