We previously introduced the idea of these pressures in the lungs, and specifically, we talked about intrapleural pressure, that negative pressure that keeps the lungs from collapsing. Well, now we want to talk about a couple more pressures, and we want to get into some nitty gritties. We want to add some vocabulary, some notation, and add some numbers to this. So we're going to start off just by saying that there are 3 distinct pressures that we want to look at when we're talking about the lung. Those are atmospheric pressure, intrapulmonary pressure, and intrapleural pressure. So we're going to go through these one by one, see how they relate to each other. Let's start with atmospheric. So atmospheric pressure and for all of these, we're going to have this notation where we can write it in shorthand. We're going to write a capital P for pressure, and then we have something in subscript that we can write. And for atmospheric pressure, it's a little ATM. So this PATM, that means atmospheric pressure. This is just the amount of pressure in the air. Now you're probably familiar here on Earth, we live in a pressurized environment. There's a lot of air pressure just pushing in on us at all times. Well, we're going to say that that PATM, that's going to be equal to 760 millimeters of mercury at sea level. Now that 760, that can vary some, and it varies some with elevation, especially. But we're always going to use this 760 millimeters of mercury, the air pressure at sea level, as, sort of, our standard physiological measure. So that's going to be our default. That also means, though, that the other pressures that we're going to talk about, they're all going to be compared to that atmospheric pressure. So as we go through these other pressures, our intrapulmonary pressure and our intrapleural pressure, we're not going to use numbers in the 100. We're just going to use numbers either plus or minus compared to 760. So if it's equal to atmospheric pressure, we'll write a 0. And if it's more than, we'll just write plus something. And if it's less than, we'll write minus how much it is. Alright. So to see how that works, let's talk about these other pressures. So the first one that we're talking about here is intrapulmonary pressure. Alright. Intrapulmonary intra means sort of within, and pulmonary means the lungs. So this is the pressure in the lungs, and our subscript for this is this capital P, and we have a subscript PPUL there for that pulmonary. Alright. So we have this diagram here reminding us of our lungs, and we also see the pleural cavities around there. This arrow, you can see, is going to the inside of the lungs. We're talking about in the lungs, the pressure in the alveoli there. So we're going to say here that this intrapulmonary pressure is going to be equal to atmospheric pressure between inspiration and expiration. So at the end of a breath out, at the end of a breath in, your for the pressure in the alveoli should be equal to atmospheric pressure, and that is because it's in, what we said, open system. Right? So in this drawing here, right, we have the trachea. This just goes up into your respiratory tract. That's by default open. So as the lungs change size, air just moves in and out, and it equalizes to atmospheric pressure. So the difference here from atmospheric pressure, how we write this out, we're going to say sort of by default, it's 0. So this should be equal to atmospheric pressure. Now as the lungs change size, we're going to go into a lot of detail coming up, that pressure does change a little bit. It goes up or down, so plus or minus, by about 2 millimeters of mercury. Some text say plus or minus 1.5, somewhere in that range. Alright. So intrapulmonary pressure, by default, equal to atmospheric pressure, but it does go up and down just a little bit around that zero one. Alright. Our next pressure here is intrapleural pressure, and intrapleural intra within, plural within that plural cavity. And our, notation for this is the capital P, and then in subscript, lowercase PIP. This is that pressure in the plural cavity. And we're going to say here that that pressure is going to be less than intrapulmonary pressure. So intrapleural pressure is always less than intrapulmonary pressure. And in our diagram here, we can remember that intrapleural pressure is in this pleural cavity here, in that purple part here surrounding each lung. And that is less than intrapulmonary pressure because of that negative pressure that we talked about that's created by resisting the recoil of the lungs. So remember, those lungs are elastic. They're naturally recoiling, sort of shrinking down smaller, but you have that sort of like vacuum sealed bag stuck between the lung and the chest wall. And as that gets pulled apart, it creates that little bit of suction, which creates that negative pressure and resists that recoil. So for the values here, we're going to say the difference from atmospheric pressure here, it's going to be in the range of negative 4 to negative 6 millimeters of mercury. K? Again, always negative. Now importantly, we're going to say here as long as that intrapulmonary pressure is greater than the intrapleural pressure, the lungs are going to stay inflated with air, and that's important. You don't want your lungs to collapse. If these two numbers are ever equal to each other, that means that the recoil can sort of win out in that relationship, and the lungs will start to shrink down, and the space in that intrapleural cavity will become greater. And as that happens, that creates less space in your lungs, and, well, you can't ventilate your lungs properly, and that's bad. We're going to look at an example of how that happens. Come on up. You should check it out. See you there.
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
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- 22. The Respiratory System3h 20m
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- 25. The Urinary System2h 39m
- 26. Fluid and Electrolyte Balance, Acid Base Balance Coming soon
- 27. The Reproductive System2h 5m
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- 29. Heredity Coming soon
22. The Respiratory System
Pressure in the Lungs and Pleural Cavity
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