 Hi, you guys. So today's lecture is going to focus around the concept of blood pressure. In the last two lectures, we've been dealing with the heart or the cardiovascular system, and this one is moving away from the heart to a characteristic of blood, a quality of blood that is tightly regulated and maintained within a homeostatic range. Blood pressure is generated by the heart, so when we talked about the mechanism by which cardiac muscle contracts, that's going to come back to us when we have this conversation about blood pressure. Before we begin, we probably should define pressure. This is a concept that truly today we're introducing blood pressure. We're going to start talking about all different kinds of pressures. Pressure is essentially a force applied over a certain surface area. So if you know a force that you apply to something with a pow, that is a very massive force, I must say, and then you know the surface area to which you are applying that force, you can calculate the pressure. Pressure is usually measured in something like atmospheres or in physio we're often going to measure our pressures in millimeters of mercury. So this is just a unit of pressure. Now I'm going to give you a little analogy. What? Me? Analogies? I know this is shocking to you, but I'm going to give you an analogy to help you kind of visualize this concept of pressure. The force can come from anywhere. In my analogy, my body weight is going to be the force, and I'm going to apply a force to your hand by standing on your hand with my foot. Now, do you agree that no matter how I stand on your foot, no matter what I do to stand on your, excuse me, I'm standing on my foot and my foot is upon your hand. My foot is on the ground and I am standing upon it. No matter what I do, unless I like jump up and down or grab a whole bunch of bricks or something and like hang on to heavy things, I won't do that to you. I'll just stand on your hand. The force that I am exerting is my body weight. My body weight is the force that's pushing down on your hand. The surface area, I can actually modify that, that's the kind of shoes I'm wearing. So I'm going to give you two choices. You can either have me, okay, watch me try and draw this crazy scene. You can have me stand on your foot, oh, good Lord. Yes, indeed, I know exactly what I'm drawing. What is this? Well, it's a little bit sketchy, but this is an attempt to draw a diving flipper. If I were to stand on, in fact, if I were to stand on your hand with a diving flipper, I mean, I can kind of be like, well, yeah, it'll probably hurt a little bit, but you know, okay, whatever. Or I can stand on your hand wearing, yeah, what's that? That's something honestly, whether I was standing on your hand wearing diving flippers or stiletto heels, it doesn't matter, because I'm probably going to kill myself wearing either of those items of footwear. But you have a choice, go ahead and tell me true. Do you want me to stand on your hand with that area, that surface area, or with this surface area? Which would be probably, and my force that I'm applying is the same because it's my body weight. So do you agree that, I mean, there's like no question, I could probably, my body weight could probably, and a stiletto heel could probably poke a hole in your hand. If I stood all my body weight on your hand with that stiletto heel. The surface area here, let's just say it's like one centimeter squared. That's my surface area on that thing. A diving flipper? The surface area here is like, I don't know, one foot squared. I mean, that's a huge surface area compared to the stiletto heel. And the point is that my force that I'm applying is the same, but clearly the pressure is different. I hope that you see that, yes indeed, go ahead Wendy, stand on my hand with the diving flipper if you must stand on my hand with something, not the stiletto heel because I'll poke a hole in your hand. That's the concept of pressure. Now, pressure of fluid. I mean, diving flippers, awesome. Well, fluid can apply a force, especially to the walls of the tube that it is contained by. And then the amount of surface area in that wall, that's going to be the measurement of blood pressure. Our units for blood pressure are going to be millimeters of mercury. Now, a couple of things to think about. First of all, low blood pressure is known as hypotension. And hypotension, hypolotension basically results in low perfusion. What is perfusion? Basically capillary exchange. If you have low perfusion, you don't have enough pressure to drive your blood through the blood vessels, through the capillaries, where gas exchange and nutrient exchange take place. Now, do you want low blood pressure in your brain? Do you want low perfusion in your brain? Your brain does not want that. Your brain needs oxygen, it needs glucose, and if you have low blood pressure to your brain, it's not getting enough of the nutrients that it needs and it's not getting rid of all the garbage that it needs to get rid of. So what's going to happen to you? Have you ever stood up and all of a sudden you get all lightheaded and you're like, whoa, I almost passed out because of low blood pressure when you change your sitting and standing? Usually that means go get some water. Like you are probably dehydrated and you can probably deal with it by increasing your body fluid volume. That will help. High blood pressure is just as bad as low blood pressure. High blood pressure is more of a chronic thing. It is hypertension. And the problem with hypertension is vessel damage. So if you imagine like taking, oh, imagine a balloon, like a water balloon hose type thing, but kind of a thin floppy hose. And if you just trickle water through the hose with low pressure applied to the walls of your little blood vessel balloon thing that you stuck to the ends of it, I mean, you're going to be fine. Like that's not going to do anything. You probably are going to have low profusion, but whatever. You've seen those drip hoses. You know, what are those called? Like the things that you lay out, you attach them to your faucet in your garden and then they just like leak. They're like leaky hoses. But you put them in your garden and the whole point of them is to water your garden. But you probably aren't going to have a whole lot of leakiness if you have low pressure pushing out of your, like a low amount of water coming out. But if you increase the amount of water coming out of your little water balloon tube, can you imagine that you could actually break your balloon? Like you could do damage to the vessel wall if the pressure is too high. The vessel damage is associated with cardiovascular disease. Atherosclerotic plaques, hardening of the arteries happens in places where blood vessels are damaged. Damaged blood vessels lead to an inflammatory response. That inflammatory response initiates like plaque formation. They've done studies to look at where your arteries harden and they're likely to have atherosclerotic plaques in places where there's a high pressure and a lot of turbulence in the blood. So the blood is like going around a crazy corner, like in a waterslide and you get like the twirly, crazy, whirly twirliness. That turbulence that you create, that can do damage to your blood vessels. Changes in blood pressure. If you experience hypotension or hypertension, outside of the homeostatic range, your body detects that change with baroreceptors, which are sensory receptors that detect pressure changes. Baroreceptors in your blood vessels detect changes in blood pressure. Send the message to the medulla oblongata in your brain, which is basically the integrator where the information is processed and the medulla oblongata sends a message out to blood vessels and heart and remedies the situation within two heartbeats. Blood pressure changes. Your body receives the information. Two heartbeats later, your blood pressure is back within homeostatic range. That's how important it is to your body to maintain blood pressure and that's why we're going to spend an entire lecture talking about this concept. All right, let's talk about, it's important to bring back your blood vessel anatomy so that we can have a visual for what are these blood vessels that we're dealing with so that we can have context for the pressure.