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Studying for a test? Prepare with these 15 lessons on Circulatory system diseases.
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Video transcript
So we were talking in a previous video about hypertension and the damage that it causes on the body. And what I'd like to do is pick up where we left off and finish that conversation. And we had kind of divided things up into receiving high blood pressures and generating high blood pressures. And receiving high pressure-- really, that means the vessels, right? That's where the pressure is going to be seen. And so the vessels can get damaged. And we talked about some of the different ways that that can happen. And in fact, there are the larger arteries and also the smaller arteries. But now, let's focus our attention on generating high pressures. Because this might be less intuitive, but actually making the pressure go so high is not an easy thing to do. And it's actually a very challenging task for the heart to accomplish. And in trying to figure it out, sometimes the heart can run into troubles. So there was an equation, and that equation was delta P equals Q times R. And I thought we had put some words to this equation. So the idea that delta P-- that's basically saying the arterial pressure minus the venous pressure. So if you have blood and it's exiting here, and that's got a certain pressure on it. And as it enters again on the other side into the atrium, it's got a pressure on the venous side. So we're saying that the pressure leaving in the arteries minus the pressure returning in the veins is what's going to help you take a certain flow of blood, Q, past the resistance in the vessels. So that's a way of thinking about it. And specifically-- let me actually draw out some of this resistance. You have, of course, resistance once it gets into the arteries. And so you've got some, R, resistance there. Then you've got more resistance once you get into the arterioles. In fact, I'm going to triple underline that one because there's lots of resistance in the arterioles. And then you've got resistance in the capillaries, and you've got resistance in the veins. And then you've got the blood returning into the venous side. So there's resistance in the circulatory system. And there's a flow of blood that you're actually trying to move around, right? So anything, anything at all, that increases the resistance or increases the flow is going to force the amount of pressure you have to put in on the arterial side to go up. And now if I draw it out, you'll see even more clearly why this is a problem. So if you have, let's say, the left ventricle, and I'll leave a little space for the valves. And this is the chamber of the heart that's doing the pumping now. And it's pumping the blood out into the aorta. This is the aorta. And this is another valve. And this valve is called the aortic valve-- pretty easy to remember name, aortic valve. And it separates the aorta from the left ventricle-- LV for Left Ventricle. So the left ventricle is basically going to have to try to get blood through this door, through this valve. And the way to do that is to apply a force to that blood and force it through that door. Now, the aortic valve has a certain area. And so if you remember, any time you have a force over an area-- I'll write that over here-- anytime you have a force over an area, you have a pressure. And in this case, that is the arterial pressure. So when I talk about arterial pressure, I'm actually talking about the force that the left ventricle generates on that aortic valve, that area of aortic valve. So now, think about it. If you have, let's say, more resistance. Let's say there's lots and lots of resistance in the vessels, so that all these numbers are slowly going up, up, up. Well, that's going to cause the overall resistance to go up, and now the left ventricle has to put more force. Or you could say, what if you have larger flow? You actually have a larger volume of blood you're trying to move around. Again, the aortic pressure is going to have to go up. So the way that the left ventricle accomplishes this or tries to accomplish this is by basically building more muscle. So this is one strategy. It'll say, OK, well, if I need to generate more force, why not generate more muscle? So this becomes very muscular in here. If you actually look at a heart that has had high pressures over the years, oftentimes you have what's called left ventricular hypertrophy. So on the surface, this sounds great, right? Left ventricular hypertrophy sounds like you're making the muscle of the heart stronger. And that sounds like a good thing. You know, that's certainly why I go to the gym. I want my muscles to get bigger. So it's confusing, then, to hear that that's not a good thing, and here's why. So now, imagine you have all this muscle, and you're feeling really good. But then I tell you that, well, this muscle's using more oxygen. So it's using more oxygen. But you notice I didn't draw any new blood vessels yet. So there are no new blood vessels getting oxygen to this muscle. But the muscle is definitely using a lot of energy, and it needs a lot of oxygen. And so what happens is that you have areas where blood is basically able to get to those areas and other areas where blood is not able to get there. And where the blood is unable to get enough oxygen to that heart muscle, you could have a heart attack or a myocardial infarction. So left ventricular hypertrophy is a way of compensating for needing more force. But it comes with a little bit of a risk because now you might have a risk of an MI or Myocardial Infarction. The other possibility is that the left heart doesn't compensate, and you have what's called left heart failure. And what that basically means is that the left heart says, you know what, I can't generate the pressures that are being required to move all that blood around, and so I won't. I won't generate those pressures. I'll do the best I can, and maybe I can't move, let's say, six liters of blood around the body, but I can do 5 liters or 5 and 1/2 liters. So it'll try to do what it can to move as much blood as possible, but it is essentially not compensating completely. And that's why you sometimes see people with heart failure after having years and years of high blood pressure. Their heart simply can't keep up. And so you experience heart failure.