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- [Voiceover] So first let us get familiar with the image that I have drawn here and you'll see that we have an image of our lungs and if you look, you see we have our right and our left lung. If we start from the top, you can see that we have our large airway here, also known as our trachea. And that trachea, or that airway, is going to break off into two larger airways, so one going to the right, and one going to the left. And those airways are gonna branch off to even smaller airways, and at the end of these we have these very tiny sacs and we call these alveoli. I'm gonna draw those in in just little blue dots, that way we can see, and these tiny sacs that we have are really our air sacs and this is where the gas exchange occurs, so this is where oxygen and carbon dioxide is swapped back and forth. Now if we're able to step outside of our lungs, let's talk about the anatomy there. So for this, let's just focus on our right lung. Now, covering our right lung, and pretty snugly covering it, we have this thin membrane called the visceral pleura. And this visceral pleura is really like a tightly fitting sac that our lungs sit in, both our right and our left lungs. Now on the outside of our visceral pleura, we have a second membrane, and that membrane is called the parietal pleura, and this parietal pleura is the membrane that covers both the visceral pleura and the lung. So think of it like this: imagine that this lung represents your hand and you slip on a latex glove over your hand. Well that first latex glove that you put on would represent the visceral pleura. If you slipped on a second glove, that second glove that's covering the first and your hand, that would represent the parietal pleura. Now when you hear the term visceral, just think of organ and in this case the organ that we're referring to is the lung. Now I'm gonna zoom in just a little bit here so we can see the space that we have. And we call this the pleural space. This is really more of a potential space that we have in-between the membranes. Now when we use the term potential, what that really means is that there is an opportunity for something to occur here. And we're gonna talk about that in a little bit more detail. In this space, we actually have about one to two teaspoons of fluid. We call that pleural fluid, and this is completely normal. This really acts as a lubricant to help these two membranes glide smoothly across each other as the lungs expand. Because remember this, when we take a deep breath in, the lungs are going to expand, these two membranes are going to touch each other. Without a lubricant, there's really no smooth barrier and these two membranes would stick to each other and they would rub and cause a lot of friction that would be definitely very uncomfortable. So this little bit of fluid that we have in the pleural space really just acts as a lubricant. Now let's shift over and look at the left lung. We're gonna draw the same membranes that we have. So we're gonna draw the visceral pleura going around the lung and we're gonna draw the parietal pleura going around that. Now, what happens if the fluid that we have in the pleural space builds up? We have an excess of fluid, what's gonna occur? Well, let's create that scenario. So I'm gonna take away our membranes, and I'm just going to add in a lot of fluid right here at the base of the lungs. Then, let's put these membranes back and see what happens. So you'll see that the area that I've drawn in with all those excess fluid has actually caused our lung to shift inward a little bit and if you compare it to our right lung, you can see that the shape of the lung on our left has actually changed. And that's as a result of this excess fluid that's sitting in the pleural space. Now remember our outermost layer is the parietal pleura. But the parietal pleura lies right against our chest wall. So as we have this increase of fluid building up in the pleural space, the pressure's not gonna push outward towards our chest because it really doesn't have anywhere to go. It's covered by ribs and muscles. Instead, the pressure, this excess build-up is going to push inward against our lung. And this can cause our lungs to shift a little bit. So I want you to think about what could possibly happen as a result of this. How would this person manifest? Certainly we would see things like difficulty breathing, and we call that dyspnea, Chest pain could be expected as well as we have this shift of the lungs as we have this build-up in pressure in our pleural space. We do have pain receptors in this area so we would feel that. This person may actually have a cough as well, and the type of cough that we can expect to see would be a dry cough versus a wet cough. And why that's important is because when there's a decrease of air space, in this case, the lungs have shifted inward, our body's able to recognize that. And as a mechanism, you're going to elicit a cough. And that cough is really an effort of the lungs to try to clear the air space. It feels like there's not enough so it's gonna try to cough to clear it out. But in this case, the problem exists on the outside of the lung, not the inside so nothing's gonna come out. Now you might be thinking, "How does this happen? "How do we have a build-up of fluid in this space "if normally we have such a small amount?" Well, our lymph system really helps to filter and regulate the fluid that we have in this area. So if something happens with our lymphatic system, that it's not able to filter out fluid as rapidly as it should be, we can have a build-up of fluid. In the event that somebody has a medical problem, like congestive heart failure or liver failure, that back-up that occurs in our vessels can actually cause fluid to leak out into the space. Somebody that has pneumonia, which is an inflammatory disorder, that inflammation in the lung tissue can actually cause fluid to seep out as well. And all of that will end up in our pleural space and cause an excess build-up of fluid, and we call that a pleural effusion.