As we introduced ventilation, we said that lungs are these elastic passive organs that change size in response to the changing size of the thoracic cavity. But that leaves us with this question: if the lungs are passive and elastic, how do they stay open? Why don't they just collapse? And we're going to say here that there are inward and outward forces that balance to keep the lungs open, because the lungs' natural tendency is going to be to collapse. You've almost certainly heard of somebody having a collapsed lung. That's something that can happen if these forces are not balanced. So, we're going to say, first, there are two types of forces. There are inward and outward forces that we want to balance here. So, we'll start with these inward forces. So, again, the lungs' natural tendency is to collapse. This elastic thing is going to try to get smaller, and that's for two reasons. First, well, elasticity and recoil. So in the lungs, there's a lot of collagen. There's a lot of connective tissue. Collagen is that protein that's strong like a rope, but also importantly, this protein elastin. Remember, elastin is this protein that's like a rubber band, and so a rubber band is always going to be trying to shrink down to its smallest size. Now, there's also going to be surface tension. Now, inside the alveoli, the surface of those alveoli is going to be covered in fluid, and so there's surface tension in there. Surface tension is just sort of that natural tendency of liquid water to stick to itself. And so all the edges of those alveoli are sort of naturally going to want to stick to each other because of that liquid. That will lead to the lungs collapsing. So, we're going to say here that the surface tension pulls the alveoli together or closed, you can say. Now we just do want to note that this is reduced by something called surfactant. Surfactant is some proteins that are put into that fluid by the body, and it sort of breaks up the surface tension a little bit sort of like soap in water. Now, it doesn't break up all the way though, importantly, but it does reduce it a little bit. Okay. So that's our inward forces. Our lungs are naturally trying to collapse, but we also have these outward forces, and this keeps the lungs from collapsing. And the main thing that we're going to talk about here is what we call intrapleural pressure. Alright. Intrapleural pressure all has to do with the pleural cavity. So, we're going way back to remember when we talked about the serosa, the linings of the organs, the lining of our body cavities? A pleural cavity is this sort of wet vacuum-sealed bag that surrounds the lungs. So, we can see here in orange, we're sort of representing the size of the thoracic cavity. And then in purple here, we have what are the pleural cavities, the pleura, the membranes that surround these lungs. So, remember, in these pleural cavities, the pleura, there's sort of two sides to them. There's the visceral pleura, which is attached to the lung. Remember that word viscera? That sort of means the body's organs. So that visceral side is sort of right up there, sort of superglued to the lung, and the parietal pleura, we're going to say here, is going to be attached to the chest wall. So, we have these two linings of the membranes, both sort of super glued, one to the lung and one to the chest wall, and between them, there's going to be a fluid. Just a little bit of fluid that creates adhesion. So much like that surface tension. Right? This water is sticking together, and it's going to stick this between this visceral and parietal pleura. Alright. So, to model this, I'm going to I'm going to do a little model here. I'm going to put a glove on this hand, and you can see this glove says chest on it. So, this represents my chest wall. I'm going to put a glove on my other hand,
Table of contents
- 1. Introduction to Anatomy & Physiology5h 40m
- What is Anatomy & Physiology?20m
- Levels of Organization13m
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- Introduction to Tissues & Histology16m
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- Simple Epithelial Tissues1h 2m
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- Identifying Types of Epithelial Tissue32m
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- Introduction to Connective Tissue36m
- Classes of Connective Tissue8m
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- Primary and Secondary Response of Adaptive Immunity21m
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- Regulatory T Cells10m
- 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
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- Introduction to Cellular Respiration22m
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- Cellular Respiration: Pyruvate Oxidation8m
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- Cellular Respiration: Electron Transport Chain14m
- Cellular Respiration: Chemiosmosis7m
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- 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
Pressure in the Lungs and Pleural Cavity
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