Welcome back. This is our first on several videos about the respiratory system, and so we're going to start off talking about the general anatomy of the lung and then some of the mechanics of breathing, how we get air in and out of our lung. Obviously, one of the main roles of the respiratory system is to bring in oxygen so that we can do oxidative metabolism, and then to remove the carbon dioxide that we produce. However, we're also going to be talking about the very important role of the respiratory system in regulating our pH, and then also keep in mind that because we are bringing in so many liters of air a day, ten thou-, around, roughly 10,000 liters a day, and our lungs have such a large surface area, that the, this is a major site of concern for our defense system, for our immune system. And so the respiratory system is going to have certain strategies that it uses to protect itself from pathogens. And that's something we're not really going to focus on, but keep in mind that that is an important thing that, an important factor that the respiratory system has to keep in mind. Now, we're going to see many similarities of the respiratory system to the cardiovascular system because, again, we're going to be talking about flow. And so we're going to be talking about pressure gradients and that the amplitude of that pressure gradient or that the amount of the pressure gradient is going to be important, as well as the resistance. And again, the, the resistance is going to be related to the radius of the tube, and the radius is going to be to the 4th power. So the radius is going to make a huge difference in the resistance of the system, and again, we'll be addressing that in similar ways that we did for the cardiovascular system. So just in a very low-mag view of the anatomy of the respiratory system, it's going to start with the nose and mouth where air enters the body, and then it's, the air is going to enter the trachea, which is going to be a tube that is, got surrounded by rings of cartilage. And then the trachea will branch into bronchi that are also surrounded by cartilage, and then those will continue to branch more and more until we get to what's called the respiratory part of the lung, which we'll be talking about in a moment. And then keep in mind also, we're going to be talking about the diaphragm, which is going to be sitting underneath the lungs, and which is going to be skeletal muscle. So we will be talking about the respiratory system by dividing it into two parts. One is going to be the conducting part which is going to contain about 150 mills of air. And as its name suggests, one of its main roles is to conduct or bring air into the main part of the lung that is going to be responsible for exchanging gas with the blood. So that is certainly one of the roles of the conducting portion of the respiratory system, is to distribute air into the rest of the lung. The conducting portion is also going to warm and moisten the air, and we'll talk about that a little bit more in future sessions. And it's also going to have a major role in cleansing the air. So again, this gets into the idea that the lung has got to be concerned about all these liters and liters of air that it's bringing in. And so the conducting portion is going to cleanse the air using what's called mucociliary transport. Which is going to be when some cells lining the conducting portion, the trachea and the bronchis, are going to be producing the mucus and then that will trap debris and then there will be other cells that have cilia that then take that mucus that it contains the debris and beats it up towards the entry way of the respiratory system. So that's the mucociliar transport system where we have mucus and cilia that are going to work together to remove particular matter and pathogens. The other aspect of the conducting system is that in particular the bronchioles, very similar to the way the arterioles controlled the flow through the system based on changing its diameter. The bronchioles are going to also have smooth muscle around them which is going to help determine how easily air flows into the lung through changing their amount of contraction or relaxation of that smooth muscle. So, those are the roles of the conducting portion of this system. Then the largest volume is going to be in the respiratory portion of the respiratory tract, which is going to be about three liters, kind of at rest, where we're going to have gas exchange. Where the, and it's going to be made up of alveoli that have a very thin epithelium that allows for diffusion of gases between the alveoli and the capillaries that are going to receive and dump off gases. So, lets talk a little bit more about the structure of the alveoli. So in this diagram, we have three alveolar sacs. So each one of these structures would be an alveolar sac, and you can see that it's a spherical structure that is then made up of smaller spheres and each of these smaller spheres is an alveolus. So the alveolar sack is made up of lots of different alveoli. And the inner surface of these alveoli is what's in contact with the air. And then you can see how the outer surface is just covered in capillaries. The inner surface of the alveoli makes up a large surface area. So it's about 70 square meters in the lungs, which is obviously going to allow for a lot of gas exchange since we have a large surface area. And that surface is going to be comprised mostly of type one cells that are going to make the surface of the alveoli that is in contact with the air. And these cells are going to be very flat cells. So they're going to be the epithelial cells of the alveoli. They're very flat and thin so that the air does not have to go a very long distance to cross the type one cells. In between the type one cells will by type two cells that don't cover as much of the surface area of the alveoli, but they're there as stem cells and as cells that produce surfactant. And we'll be talking more about surfactant in the future. So you can see how we have this thin epithelium and then lots of capillaries on the other side of it to exchange the gas between the air and the blood. We're going to move now to talking a little bit more about ventilation and how we get air in and out of our lungs. And it's going to be really important to remember that the way that we get air into our lungs is called negative pressure breathing. So basically, what we're going to do is we are going to take our diaphragm, which is a dome-shaped muscle, and contract it. And so, it's skeletal muscle, and if you contract it, that's going to make it shorter, and it's going to become flatter. So as it becomes flatter, then that is going to cause the chest wall to expand. And as that chest wall expands, then that is going to lower the pressure in the lungs. So you have negative pressure in the lungs, and that means that air is going to flow into the lungs. So the diaphragm is what's going to be very important when we're just doing normal activities like sitting and watching me lecture where you're somewhat at rest. You're going to contract your diaphragm to inhale and then you're just going to relax your diaphragm to exhale. And we'll be talking more about this. But if for instance you're exercising you're going to want to take a deeper breath. And you are going to want to breathe more quickly. And that's when you bring in muscles of the rib cage that are going to kind lift the ribs, kind of like a handle on a bucket. And you lift it. And that's going to increase again the volume in the lungs. And then you can also use when you're trying to exhale quickly, many other muscles of the chest wall, as well as the abdomen. So depending on the type of breathing you can do, you're doing, you might use more muscles, but very often just in normal rest breathing, you're using primarily the diaphragm. The other thing that, to keep in mind, and we'll be talking much more about this, is the reason why you can kind of just relax your diaphragm, and everything just com, compresses, the chest wall gets smaller on its own, is because of the elastic recoil of the lung that makes the lung want to get smaller, and that's what helps in that passive exhalation process. And we'll be talking more about that in future sessions. So here's another view of this, where if we contract the diaphragm, we're going to expand the chest wall. That's going to, because of Boyle's Law, cause the pressure in the lung to go down. And that means that we're going to have a greater pressure out in the atmosphere and that means air is going to flow in. So that's inhalation. Negative pressure breathing. And air is going to enter when the pressure outside in the atmosphere is greater than the pressure in the alveoli. So P capital A refers to the pressure in the alveoli. We're going to be using this abbreviation a lot, so it's good to get used to it. When you inhale and then you often kind of pause before you exhale, then very rapidly the pressure will equilibriate between the alveolar pressure and the atmospheric, -phere pressure, and so, flow will become zero. So in between breaths, that's what's going to happen under most circumstances. When we expire, then that's going to be usually passive under normal conditions, and that's just when the thoracic cavity, the chest wall, and the lung are going to return to their normal dimensions. And as that happens so the diaphragm is going to become dome-shaped as it relaxes. That's going to increase the pressure in the lungs and that will make its pressure greater than atmospheric pressure and so air will flow out. So that's what's here where air leaves when atmospheric pressure is less than the alveolar pressure. So let's talk about ventilation, which is going to be this exchange of air between the atmosphere and the lungs. And we can talk about a ventilation cycle, which is going to be one inhalation and one exhalation. And we'll be talking some about the frequency of ventilation, how many breaths per minute are you taking. Often it's going to be between ten to 18 breaths a minute. We'll also be talking about tidal volume, which is how much air you're inhaling or exhaling and that's going to often be about a half a liter per breath. And so using the tidal volume and multiplying it by the frequencies, frequency of breathing, then we can determine a minute ventilation, how much air are you bringing into your respiratory system each minute. And so if you're breathing half a liter a minute, ten times a minute, then that's going to be about five liters a minute. Keep in mind, and we'll be talking about this some, that the depth and the rate of breathing can change, and this can dramatically increase air flow, twenty-fold. And then blood flow can increase three-fold to the respiratory system. So during heavy exercise we can make a huge adjustment in basically the minute ventilation. However, if you are going to do that, you are going to need to have active exhalation. You don't have time to let everything slowly relax and let the recoil of the lungs happen. You are going to need to have to be able to squeeze out that air so that you can quickly take another breath in. And so that will require those abdominal muscles and the intercostal muscles between the ribs. So, let's finish this up by just reviewing what we've talked about where we're going to have this huge interface for gas exchange with the lung. And we've talked about how it's going to contain a conducting zone, which is what we're going to call dead space because it can't exchange gas. And that's going to have an alveolar space, which is the respiratory zone, and we'll be talking more about that. We've talked about some of the basics of how we use negative pressure breathing to get into the lung, and then how we exhale. And then how we're going to have passive exhalation if we're at rest but then during exercise that we're going to need active exhalation. And that one reason why we can have passive exhalation is because the lungs want to recoil, and so that's going to help drive that process, and we'll be talking more about that in future sessions. [BLANK_AUDIO]
