Now that we understand Boyle's law, we understand how changing the volume of the lungs is going to change the pressure, and that will force air in and out of the lungs as part of ventilation. But we previously defined some very specific pressures. So now we want to go through and look at these and see how they change as part of ventilation and put some values next to those definitions. Alright. So we're going to start off by saying that ventilation alters pressure gradients, but importantly, we're talking about pressure gradients with respect to atmospheric pressure. And remember, we have this sort of notation for writing atmospheric pressure, this capital P, and then in subscript that lowercase ATM there. Alright. So other pressures are going to change, but atmospheric pressure, the pressure in the air around us, is always going to be 760 millimeters of mercury, at least at sea level. At least it's not going to change in response to any physiological changes. It's going to be constant as you ventilate your lungs. Now the pressures that are going to change are going to be the intrapulmonary pressure and the intrapleural pressure. So remember, intrapulmonary pressure, that's that pressure in the lungs in the alveoli, and we have this shorthand for writing that that capital P, subscript, lowercase Pul there. Well, so in the lungs, as we change the volume, that intrapulmonary pressure, we can expect that to change as a result of Boyle's law. But remember, inside the lungs, we said that this is an open system. It's connected to the atmospheric air through our trachea, our respiratory tract, and that's naturally open. So yes, that pressure is going to change, but it's always going to equalize. When I say here, it equalizes to atmospheric pressure as air moves in and out of your lungs. Now our other pressure here is going to be intrapleural pressure. That's that pressure in the pleural cavity, that cavity surrounding the lungs, and we have this shorthand capital(lowercase Pip for writing that. Now remember that cavity is basically, we said, like a wet closed vacuum. So that means that this cannot equalize to atmospheric pressure. Alright. So now we're going to just follow these two pressures around sort of through one cycle of breathing, 1 inspiration and expiration. So we have this graphic here where we're going to do it. So you can see here on the top, we see inspiration. On the bottom, we see expiration, and we have graphics here showing the lungs. You can see during inspiration, we can see those lungs are getting bigger. During expiration, we see those lungs are getting smaller. And then we have 2 other places. We have between expiration and inspiration. So that's over here on the left here. You can see the lungs are really small there. That's after you breathed out, but before you started breathing in again as you're just sorta sitting there with sorta smaller lungs with not a lot of air in them. And then over here, we have between inspiration and expiration on. On the other side, this is sort of after you breathe in but before you started breathing out again as you're just sitting there for, you know, half a second with large lungs that are nice and filled there. Alright. So we're going to follow this around, and we're going to start over here on the left, again, after expiration but before the start of inspiration. So let's fill in some values. So atmospheric pressure is 760 millimeters of mercury. It's always going to be 760 millimeters of mercury, so that's easy. Alright. But what about the intrapulmonary pressure? Well, after expiration but before inspiration, this is when your lungs have time to equalize. So air is going to be in this case, it will have moved out of the lungs until that pressure is equal. So we're gonna say that this is with respect to atmospheric pressure, our intrapleminary pressure is going to be 0. It's gonna be equal to atmospheric pressure. But what about our intrapleural pressure? Remember, that's that pressure in this what we see here in purple, showing that pleural cavity around the lungs. Well, remember that intrapleural pressure we said is always negative, but it's negative because the lungs have recoil. They have that elastin protein pulling on the pleural cavity, and the more it pulls, the more negative that that intrapleural pressure is going to be. But here, we see the lungs are actually they're sorta they're smaller than they they are at other times during the cycle. They've gotten smaller, and so that elastin protein isn't stretched out as much. There's less recoil. So at this point, this value is going to be negative 4. Our intrapleural pressure is gonna be negative 4 millimeters of mercury. Alright. So now that we set that up, let's follow along. Well, now we breathe in. So we go through inspiration here. You can see in the drawing here, the lungs are getting bigger. We have those arrows, sorta, pointing out, showing the lungs are expanding. Well, atmospheric pressure doesn't change, but the volumes of the lungs are increasing, which means the intrapulmonary pressure must be going down. The intrapulmonary pressure is gonna go down as far as negative 2 millimeters of mercury with respect to atmospheric pressure. Now you'll see that sometimes, some texts say negative 1.5, some say negative 2, somewhere in that range there. Alright. What about intrapleural pressure? Well, as the lungs get bigger, they recoil more because you're stretching out that elastin protein more. So at the beginning of inspiration, we were at negative 4 millimeters of mercury, But by the end of inspiration, this is gonna get more negative as that elastin protein recoils more and more, and it's gonna reach as low as negative 6 millimeters of mercury. Alright. Well, let's keep on going. So now we've finished inspiration. That volume has gone up, but because the volume went up, the pressure went down, and this means that air was flowing into the lungs. So now we're over here. The lungs are at the biggest state, and air has flowed into the lungs. Well, the atmospheric pressure, that doesn't change 760. But what about that intrapulmonary pressure? Well, that air flowing into the lungs, that is what equalizes the pressure. So at their largest state here after you breathe in, but that half second before you breathe out again, this is gonna equalize to 0 millimeters of mercury, it's gonna be equal to that atmospheric pressure. Alright. But what about the intrapleural pressure? Well, the intrapleural pressure, remember, that's a function of how big the lungs are. Here, the lungs are large. They're filled with air. They're really stretched out. That elastin protein is really recoiling. It's really pulling on that pleura, the membrane there pulling on that pleural cavity, which means that this becomes the most negative it's gonna be. It's gonna go as low as negative 6 millimeters of mercury. Alright. We followed along again. Well, now we are at expiration. We are breathing out. You can see in our illustration here, expiration. The thoracic cavity is getting smaller. We see that these lungs are getting smaller. We have these arrows there. Oh. Atmospheric pressure hasn't changed, but if the volume of the lungs is going down, what's going to happen to the intrapulmonary pressure? The volume goes down, the pressure goes up, and it will go as high as positive 2. Again, some text will say positive 1.5, 1.5, 2, somewhere in that range there. Alright. The intrapulmonary pressure goes up to positive 2, but what about the intrapleural pressure? Well, as the lungs get smaller, there's less recoil. So it starts at that negative 6 when they're big, but as they get smaller, it becomes less negative, and it ends up at negative 4 there. Alright. We can finish our cycle around. Well, the pressure went up. That means that the air was being forced out of here. So when we make it all the way around, now we're back over here. The air gets forced out. That's when that pressure equalizes. So that's why this intrapulmonary pressure again is at 0 here. It's equalized to atmospheric pressure. And again, the lungs here are at their smallest state, so the intrapleural pressure is less negative. It's at negative 4 millimeters of mercury. Alright. Some values there. Hopefully, that makes sense. You followed along. We are going to practice it some more and an example and practice problems to follow. Give them a try, and I'll see you there.
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
- Levels of Organization13m
- Variation in Anatomy & Physiology12m
- Introduction to Organ Systems27m
- Homeostasis9m
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- 4. Tissues & Histology10h 3m
- Introduction to Tissues & Histology16m
- Introduction to Epithelial Tissue24m
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- Structural Naming of Epithelial Tissue19m
- Simple Epithelial Tissues1h 2m
- Stratified Epithelial Tissues55m
- Identifying Types of Epithelial Tissue32m
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- Introduction to Connective Tissue36m
- Classes of Connective Tissue8m
- Introduction to Connective Tissue Proper40m
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- Introduction to Muscle Tissue7m
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- Nervous Tissue: The Neuron8m
- 5. Integumentary System2h 20m
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- 7. The Skeletal System2h 35m
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- 12. The Central Nervous System1h 6m
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- Introduction to the Peripheral Nervous System5m
- Organization of Sensory Pathways16m
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- 14. The Autonomic Nervous System1h 38m
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- 17. The Blood1h 22m
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- 19. The Blood Vessels3h 35m
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- 21. The Immune System14h 37m
- Introduction to the Immune System10m
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- Review Map of Innate Immunity
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- Primary and Secondary Response of Adaptive Immunity21m
- Immune Tolerance28m
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- Natural Killer Cells16m
- Review of Adaptive Immunity25m
- 22. The Respiratory System3h 20m
- 23. The Digestive System2h 5m
- 24. Metabolism and Nutrition4h 0m
- Essential Amino Acids5m
- Lipid Vitamins19m
- Cellular Respiration: Redox Reactions15m
- Introduction to Cellular Respiration22m
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- Cellular Respiration: Glycolysis19m
- Cellular Respiration: Pyruvate Oxidation8m
- Cellular Respiration: Krebs Cycle16m
- Cellular Respiration: Electron Transport Chain14m
- Cellular Respiration: Chemiosmosis7m
- Review of Aerobic Cellular Respiration18m
- Fermentation & Anaerobic Respiration23m
- Gluconeogenesis16m
- Fatty Acid Oxidation20m
- Amino Acid Oxidation17m
- 25. The Urinary System2h 39m
- 26. Fluid and Electrolyte Balance, Acid Base Balance Coming soon
- 27. The Reproductive System2h 5m
- 28. Human Development1h 21m
- 29. Heredity Coming soon
22. The Respiratory System
Ventilation
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