Now that we have gone through the basic structures of the respiratory system. It's time to think in a little bit more detail about how the system actually moves air, in and out of the lungs. That process is called ventilation, and in this lecture, we're going to deal with basic cons, concepts related to ventilating the lungs. What do you usually call ventilation, instead of, you don't talk about ventilation, you talk about-. >> Breathing? >> Yes, yes we talk about it as breathing, but what it's really doing is moving gases in and out of the lungs. And there are actually two phases of breathing what are they. >> Oh, inhalation and exhalation? >> Excellent inhalation and exhalation we breathe in, we breathe out, right? Okay, great now before we can think about what's going on in ventilation, we have to think in a little bit more detail about structures that we call the pleura, the pleura are a serous membrane, I haven't talked to yet about serous membranes, but what serous membranes are, are very thin membrane layers that cover the outer surface of many of the organs in the body cavity, either the thoracic body cavity or the abdominal pelvic cavity. So this very thin membrane layer, covers the outside of the lungs and at some point in the thoracic cavity, that membrane reflects backwards, it does a U turn and lines the thoracic cavity itself, okay. Now if you'd look at the picture that's opened in front of you, you can see there showing you a cross section of the thoracic cavity, and you can actually see that that layer of pleura that covers the outer surface of the lungs is called the. You see it? Naomi? >> The visceral pleura. >> Exactly, the visceral pleura. And then also you can see the layer of the pleura that lines the thoracic cavity. And what is that called, Lydia? >> The parietal pleura. >> Exactly, the parietal pleura. And then notice that in between those two layers of pleura. There is a space, what looks like a space, in the picture. It's not really an empty space, but what is that space called? >> The pleural cavity. >> Exactly, Mia the pleural cavity. The pleural cavity is filled with, pleural fluid which is secreted by the pleural membranes into the cavity. Now the purpose of the pleural fluid is first of all it allows the lungs to move against the surface of the thoracic cavity, smoothly, right? But even more important than that, it causes the visceral and parietal pleura to stick together like this. As long as we don't do anything to disrupt that adhesion force created by the pleural fluid, the visceral pleura sticks closely to the parietal pleura and so the lungs actually moves with the chest wall, okay? Can you think of anything that might cause a disruption in that adhesive force? >> Would some sort of traumatic injury cause a disruption? >> Yeah so, if we like injure the rib cage, for example and we do something to let some air into the pleural cavity that disrupts the adhesive force, and it will allow a portion of the lung to collapse that would be a very bad thing, right? We don't want that to happen and under normal circumstances, it doesn't happen the lungs just move with the chest wall. Now, why do I bring this up? I bring it up because when we ventilate, the chest wall moves, right? When you inhale, what happens to your chest wall? Yeah, Mia? >> Your chest wall moves out. >> It moves out and it moves up a little bit, right? Okay, and then, when you exhale. The chest wall moves down and in a little bit, right? Okay, so when that wall movement, the chest wall moves, think of the lungs as moving along with it, okay. Now the lungs contain a balance of fibrance and elastic tissue. And so when you inhale, what do you think's going to happen to that elastic tissue? >> It's going to be stretched. >> It's going to get stretched a little bit. And so then when you exhale, the elastic fibers and elastic components will retract back to their normal position, okay? So, how do we actually get this inhalation and exhalation to work? When you think of inhaling, I want you to think of it as being an act of process it involves contraction of muscles. Okay? Let's review one more time the muscles of inspiration and expiration, and think about what happens during inspiration and expiration, that allows us to move air in and out of the lungs. So, you probably remember that inspiration is always an active process, right? That means it's always going to require muscle contraction, yes? And expiration, if we're just sitting around quietly inhaling, exhaling, that exhalation or expiration is a passive process, right? Well, if we are breathing more vigorously and there are various conditions under which that could happen, if we're breathing more vigorously, exhalation can also become an active process, right? Okay, so the muscles of inspiration, just quiet, sitting around, breathing normally. Those muscles are, do you remember? >> The diaphragm. >> The diaphragm is the main one, exactly. So diaphragmatic contractions are responsible for most, of the increase in lung volume during inspiration so yes, that's exactly right. And then one of those between the rib muscles, do you remember? >> The intercostals? >> Yes but specifically the external intercostals, right? So those muscles the intercostal muscles cause the ribs to move up and out the diaphragm flattens when it contracts and that causes this height of the lungs to increase. Right? And that translates into a bigger lung volume. Now, when you quietly exhale, that quiet exhalation is a passive process because you have elastic fibers in the lungs that retract, and draw the lungs back into a smaller size, right? If you are out for a run doing your daily exercise, your cardiovascular workout and have to breathe more forcibly. What muscles are going to be caught in to assist with that more forceful breathing? >> Sternocleidomastoid. >> Exactly, sternocleidomastoid which is a muscle you remember it attached on the back of the skull. Posteriorly, and then it wraps around the side of your neck to attach on the sternum and the clavicle anteriorly. So, when sternoclatomastoid contracts, it can just give an extra boost to the sternum, right? Any other muscles you can remember, that are going to be accessory muscles are breathing, when we have to breathe forcefully? >> The scalenes? >> The scalenes exactly, now they're deeper muscles on the side of the neck, right? And they attach to the top two ribs, and so when they contract they help to lift the rib cage more maximally as well. Those will be the major ones, there's another muscle that I haven't mentioned to you yet, pectoralis minor. Which attaches on ribs two actually ribs three to five and it also helps to lift the rib cage when it contracts during forceful breathing. Now if we have to exhale forcefully, what are the muscles that are going to be primarily responsible for that forcible exhale? Any ideas? No? You remember the obliques? So okay, basically, what we want to have happen in a forceful exhale is we want to, draw it in on the wall of the abdominal pelvic cavity draught in and collapse the ribcage because that helps to reduce the volume of the lungs quickly. So the external obliques would be involved of the deeper internal obliques, rectus, abdominus, we have a very deep muscle in the anterior wall of the abdominal pelvic category that muscle is transversus abdominis. It runs this way across the wall of the endo, of the abdominal pelvic cavity. So those muscles are going to really pull us down into the reduced lung size quickly. Great job you guys.
