Understanding Blood Vessels and Pressure

So we're going to be talking about blood vessels, parts of the cardiovascular system. We went over heart, now we're doing blood vessels. Why does this matter in the first place? Basically, when you look at blood pressure, if blood pressure gets too high, it can cause kidney problems, it can cause aneurysms, it can lead to higher incidence of strokes. If it gets too low, people feel kind of faint. If it's too high also, it can cause damage to the kidneys because of the amount of pressure just... pushing on the glomeruli. But how do we determine if this is a good or bad thing? A lot of people will just say, I feel fine. There's nothing wrong with me, except that high blood pressure is the silent killer. People don't really experience that much discomfort except possibly headaches with high blood pressure. And so you really don't realize that you have it. I've probably had 50, 60, 70 patients. that had high blood pressure and did not even know it. Probably had 10 patients over the last 10 years that have diabetes that didn't even know it. But high blood pressure is very common and nobody really notices anything. Therefore, it's a silent killer. And so, neat little video to watch there. When you look at blood vessels, when they leave the heart, anything leaving the heart is considered an artery. Anything returning blood to the heart It's considered a vein and the capillaries in the middle are basically your direct contact with tissue cells because they're the smallest. They're so small that basically every cell in your human body is near one to where it can get the nutrient supply from it. Now, between arteries and capillaries, it's a big jump from a big artery to a little bitty capillary. So there are arterioles in between them. And then from a capillary to vein is a big jump. So there's a venule in between those. And we'll be seeing more of those in a little bit. But remember, the heart is basically sending blood out. It gets smaller, smaller, smaller until it becomes an arteriole. And then it goes to these capillary beds. Now, capillary beds are basically many, many, many little branches of vessels that are going here throughout a muscle. It could be a calf muscle or a toe, for example. And. Now, the interesting thing about this is that there are, let's change this. Let's change this to a stomach area. Let's go even intestines. Now, this is easier to kind of describe to you guys for one reason. Is it important to digest a peanut butter jelly sandwich when someone's trying to kill you? Are you getting vandalized, mugged, whatever? Running from a tiger? I don't know. Whatever causes your fight or flight response. Is it important to digest food at that point? And the answer is no. Basically, we shunt blood away from the digestive tract and put it towards skeletal muscles. So you can fight, so you can run, so you can do whatever you need to do. And so we have these little things here called precapillary sphincters. These precapillary sphincters can squeeze and basically prevent blood from going through them. And if it does that, well, blood will simply bypass the capillary bed and continue on its way back to the heart. And so this whole area can get skipped. And that's called a thoroughfare channel. And I always give the example of, I'm sorry, I'm choking on nothing. So I'm going to get me a drink here. But the Lloyd Expressway is a thoroughfare channel. It's like one of the major channels where traffic is running through Evansville. But if you closed all the exits, where would you end up? Gateway Hospital is on the opposite side of Vandenberg County heading. from USI East. So you would bypass the entire city of Evansville. Well, this is very similar. If they're putting a gate up to where you can't exit the Lode Expressway, you can't go into the city. So you would simply go all the way around. And so these are thoroughfare channels and bypassing by pre-capillary sphincters. Now, capillary beds are very wide and there's many of them. So when a blood's coming through here, it's going kind of fast. So it goes pretty quick down through. thoroughfare channel. But if we were going to capillary bed, it slows down because there's so many of these. The blood can slow down. And then we have gas exchanges of oxygen, carbon dioxide, so on and so forth. And so again, it's slowing down because of gas exchange. Now, we also see a couple of things in here. Sinusoids, we'll talk about in a little bit, but lymphatic capillaries. The reason we have these lymphatics, and we'll talk about those here in the next chapter, is that not all of the plasma coming in and going into the intercellular spaces or between the cells. interstitial fluids is what they will become. Not all of it is getting sucked back up by the vein. And that's because here it comes in at a great pressure, but it leaves as a low pressure. Some of it's left behind. And so the capillary from the lymphatics are going to suck up that extra juice. So then we go venule, vein, and back to the heart. Now, the interesting thing about a vein is nothing's pushing them. You're like, what are you talking about, Vandal? Well, here on this side, the heart is pushing the blood this way. So what? is pushing the blood back. Is it just simply the flow coming down and continuing to push it? Not necessarily. If it comes too high of a blood pressure, this might just put extra, you know, fluids in your leg and you'll end up with swelling. So what is pushing it back to the heart? And the answer is a couple things. One is there's a little bit of a smooth muscle in the wall. The other is that There is a one-way valve in veins, and so when blood goes so far, it can't back up. And the other is when you squeeze your muscles, like, say, your leg or your arm, you put pressure against it, and it pushes blood to the next area, and it can't back up. And you move your leg again, and it pushes blood a little bit farther, and it can't back up. And you breathe, and it pushes blood a little bit because your guts, you know, and things squish against it and keeps pushing. So right up here, the pressure is extremely low, almost zero. But here, it's whatever your blood pressure is, like, say, 110 over 80. That's the 110 or 120 or whatever your blood pressure is. Let's go to the next. So the blood vessels are all made up of a total, at least not all made up of it, but all of them have the ability to have all three of these layers. So they're called tunics instead of layer. So intima means inside or intimate, most intimate inside of the blood vessel. The media is very similar to a heart like myocardium is a muscle. So in the tunica media here, we're going to have smooth muscle and tunica externa, external. So it's the outside. That's pretty easy. Now, when you get down the capillaries, you might only get up to this, just the tunica intima, because one layer of simple squamous epithelium is about all the thick that the capillary is. So in the tunica intima, this is the simple squamous epithelium. And the reason that's cool is because this slick surface reduces friction. It's the same exact surface we see in the heart. We talked about inside the heart how it's slick and how blood doesn't see the collagen, and therefore it doesn't have the clotting cascade, the coagulation cascade of fibrinogen changing to fibrin and the platelets becoming sticky. So that's the same as blood vessels. All the way through, it has this simple squamous haptothelium that was basically keeping that slick lining. The same as endocardium. Exact same stuff. It just keeps on flowing all the way through. The connective tissue basement membrane. Well, the simple squamous epithelium has to be connected to something. And so we have some basement membrane there, but it says vessels larger than one millimeter. And so it can get so small. It's just one simple squamous epithelium. Tunica media. This is the smooth muscle inside. Time for some Gatorade. Smooth muscle inside. Now, the interesting thing about smooth muscle is it contracts, right? So as it contracts, it squeezes. Now as I picked up my Gatorade bottle, which I love orange Gatorade, if I take this Gatorade, and I know you can't see it, but you can envision a Gatorade bottle or a water bottle, and you put the lid on, all right, you get the lid on, and you squeeze the bottle. Now, did pressure go up or did pressure go down? My Gatorade bottle, the pressure went up. Let's talk about the inside lumen, and there was a space inside. When I squeeze this Gatorade bottle, What happens to the inside diameter? A gain goes down. That's why it squeezes on the Gatorade, and that's why pressure goes up. Remember, pressure and volume are inversely proportional, because as I squeeze the Gatorade bottle, the volume went down, pressure went up. But if I were to let go and vasodilation, the vessel gets bigger, the diameter increases, which means volume goes up, pressure goes down. That's an important thing to remember. Gosh, Gatorade sure is good. So, the bulcus layer responsible for maintaining blood flow and blood pressure is where the smooth muscle is. Smooth muscle, tunica media. Now, tunica outside, externa, is basically connective tissue to where everything, basically just holding everything together. So, here, composed mostly of loose collagen fibers that protect the wall. and anchor it to surrounding things. That makes sense. Now, it can have nerves. So if you cut a blood vessel, it can hurt. Because it has nerves. The blood vessel, as we said before on this slide right here, media, that's muscle, ladies and gentlemen. It needs blood. So the tunica externa has to have some sort of a blood vessel called vasovasorum, which is the network of blood vessels feeding and nourishing the outside layer and a lot of times the myocardium. Why did I say myocardium? I meant tunica media. Sorry, sorry, sorry about that. So here's the, I don't know what word I just made up there. It's late at night. The vasovasorum here is the blood vessels, and then the yellow is supposed to be the nerves, and this gives blood to here. We have the tunica media, which blood can go in. We have some elastic fibers versus muscle because there's different types of, let me back up. I'm sorry, I must have missed that. But there's different types of, here it is, different types of arteries. For example, elastic and muscular. The reason that this is elastic up here in the aorta is does the aorta have to contract at all? The answer is no, it does not. The aorta never really contracts. It rebounds. It's basically a huge rubber band tube. If you push a bunch of blood in there, it snaps back. It does not. It simply does not. have to squeeze at all. It just snaps back and that's its main purpose. So it's more elastic. But if you get farther down the body, there's a lot of smooth muscle to squeeze to help push and maintain blood pressure. Back to this one. Why is there elastic membranes? And the answer to that is sometimes it needs a recoil back, like we said, and in the muscle itself. Now, here's a picture of an artery. Here's a picture of a vein. Now, if you put them side by side, they're about the same size. You're like, no, it isn't. This lumen's bigger. This must be fatter. There's much more muscle. Yeah, but overall, the size is about the same. The outside is about the same. There's more muscle in the artery. There's less muscle in the vein. There is a smaller hole in the artery than the vein. You're thinking it's about the same. You're going to have to trust me that veins have a larger lumen than... arteries do veins carry more blood in them than arteries do you're gonna have to trust me we'll come back to it and what do we have here valve so this is a one-way valve blood goes one way and when it tries to back up this valve pushes open but it can't back up so the blood gets pushed from here now there's something that can go wrong if the pressure is too high And these valves maybe get older because we age. They become a little bit more incompetent. And blood pools and kind of pushes back. And so that can cause a swelling. It can cause something called a, and you know what? I can't believe I forgot the name of it. Varicose. That's a varicose vein. So varicose veins are basically the valves. Not allowing the blood to go through and having trouble backing up. All right, so here we have elastic arteries. Now remember, its job is to bounce back. And where do we find it? Up there in the aorta. Anyway, so it has a lot more elastic tissue than smooth muscle. But the muscular one, right here, not as much elastic, but much more smooth muscle. And then arterial, as it gets smaller, they lose both. Why do they have less? Because it's getting littler. It's getting smaller. So it's going to have less muscle. When you get down to capillary. okay well even arterial and a smaller arterial and there I don't know why I had archer there it's a capillary okay so this is a capillary and look at this no elastic tissue no smooth muscle no fibers it's just simple squamous epithelium that's all it is one layer of simple squamous epithelium and it's basement membrane holding it together On a venule, you see it gets a little bit more of the muscle back, and it has some fibrous layer back. Vein has a little bit of everything again, except much less muscle on a vein than on an artery, especially a muscular artery. It's almost the same as an elastic artery, volume-wise, but there's much more elastic tissue. So veins, as you see, look more like an arterial, but they have a whole lot more. As far as muscle, they have a whole lot more fibers connected to show me outside so again on arteries There's elastic, as we talked about. There's muscular and then smaller arterioles. The elastic, it says aorta and major branches. Again, its job is to bounce back like a rubber band. This huge bolus of blood gets pushed out of the heart, and it's basically a wave. And as it snaps back, it continues to push the blood forward. So it doesn't do a whole lot of... work except stretch and bounce back. The elastic tissues found in all three layers, the internal, the tunic internal, the tunic external, and the tunic media, but mostly in the media. All right, so they act as a pressure reservoir that expands and recoils. Rub band, ladies and gentlemen, allows for continuous flow downstream. In other words, it expands and then it contracts and pushes that blood along. Muscular arteries. Now, so we have less elastic tissue, more muscle. And so because there's more muscle, this is where the true vasodilation and vasoconstriction events happen. Now, it says, look at this, diameters range from pinky finger size. That's not a big artery. A pinky finger is a huge artery. Down to pencil lead size. So definitely they get smaller, smaller, smaller. But it's most of the arteries that are named except for aorta. and abdominal aorta and descending aorta, all the rest, mostly are the muscular arteries. It says it has thickest tunica media, and obviously because all the muscle, but not as much elastic tissue. And so the active for, again, muscle squeezing, vasoconstriction. You can squeeze blood vessels, and the pressure goes up. It helps propel blood arterioles. They're just getting smaller on the way. We don't name all the arterioles. They just get smaller, smaller, smaller. They have less muscle. They have less elastic tissue. They're called resistance arteries because the changing diameters change the blood pressure. Sorry, change the resistance to blood flow. Let's talk about resistance. It says the changing diameter changes resistance. Well, anybody that has ever used any kind of a pipe or any kind of a garden hose, knows a couple things about resistance and that is the longer it is the less flow the the skinnier it is the less flow so a big fat pipe has more flow in fact size diameter is the number one thing that changes resistance i'm going to say that again diameter is the number one factor changing resistance if you have a pipe and you double the size you're way more than double in the full you're way more than halving the resistance it goes to i think it's an eighth or a sixteenth it goes down considerably in in uh in change in diameter and they lead to capillary beds which of course we saw as the capillaries so let's talk about them they're microscopic they're itty bitty these things are so small that a red blood cell has to fold in half it says not only pass through i'm telling you the real truth is some of them have to fold in half to get through because it's so tight. So the wall, it says walls, just thin tunica intima. Walls are just a thin tunica intima. In the smallest vessels, one cell, one cell forms the entire circumference. It's very tight. And so how little is that? Let's think about this. If you've got pencil, the mechanical pencils, point, it's point 80, the itty bitty ones, the ultra fine ones. Very, very, very small. So parasites. I've never asked this, honestly. Spider-shaped stem cell helps to... I've never asked that, ever. Probably never will. Don't worry about that. Supplies almost every cell except for cartilage. Now, what are we talking about? Okay, I got to tell you. Highland cartilage. Highland cartilage does not have a good blood supply. That's why it wears down. If you wear out a disc or cartilage between bones, It's not going to grow back. You're just S-O-L. It's not going to grow back. I mean, you could take shark cartilage. You could take MSM. You could take all kinds of herbal stuff. And it will decrease the pain. And honestly, the best thing you can take is hyaluronic acid. We'll talk about that some other time. But you can't get that cartilage back. Epithelium has an okay blood supply because it comes through the basement membrane. The corner of your eye and the lens of your eye. Horrible blood supply. The cornea can be transplanted with almost no chance of rejection by the immune system because there's no blood supply, therefore almost no immune system. So the function of a capillary is it brings oxygen to the tissues, right? It brings nutrients. What do I mean nutrients? Glucose, amino acids. It brings, you know, sodium chloride, all these different things. But it also brings waste products and removes waste products. So more removing waste products. Hormones, as we talked about in the endocrine chapter, we're bringing the hormones to the cells and the blood. Between blood and interstitial fluids, between blood and interstitial fluid. What are they saying here? Oh, they're saying the capillary is the thing between the blood and the interstitial fluid. So blood comes in down through the capillary. It leaves through the wall, and now it's an interstitial fluid. So what is the difference here again? Blood and interstitial fluid. What is the difference? Blood is basically all the way. We know what blood is. It's got all the formed elements and such. But what is interstitial fluid? Okay. Interstitial fluid does not have proteins. And it does not have the red blood cells. Mostly it's plasma getting pushed out, but we don't call it plasma anymore. And it's nutrients and things, but we don't call it that anymore. We call it interstitial fluid. So capillaries, there's three different types. Continuous capillaries. It all depends on how big a hole there is for things to get through. Medicine does not allow much through. It says abundant in skin, muscles, lungs, and central nervous system. But in the central nervous system, there's a blood-brain barrier. And remember, these are foot cells of astrocytes that are basically causing the blood-brain barrier. But they're enclosing it with a very tight junction. And so a lot of stuff doesn't get through. And when we talked about brain, if you had my class, we talked about amino acids and some things. If they're allowed to pass through the brain, they act as neurotransmitters. And they're hyper-excite neurons and kill neurons. Horrible stuff. So continuous capillaries, we have basically the blood coming through. And it's more of a tighter junction. These are tighter junctions. I don't know what terms they use. What's it say? I don't want to say much. But it's more of a tighter junction. Oh, it does say that. Total enclosed is a tight junction. Well, what do you know? My exact words. But they don't allow much to go through. They definitely filter much less. Now, this fensterated, and by the way, that is the typical capillary throughout the body. They don't filter as much. But a fenstrate, it looks like somebody came along and drilled holes in it. And this is what you find in a kidney. This is what you find in a kidney. And it allows a lot of plasma to go through. And it allows glucose and pretty much everything to go through except, again, no proteins, no red blood cells. But it allows pretty much everything else to go through. So definitely increased permeability. These fenstrations, it says, covered with a thin glycoprotein diaphragm. Look at this. It looks like somebody drilled a bunch of holes into this capillary, and so more filtration. But there's another, and again, you're going to find it's a myelomeralis. It's typically what you're going to find in the kidney. We'll talk about the kidney in a different chapter. Some digestive organs have this because we're increasing nutrients, so you can bring the amino acids and things back to the liver, fats and such. But most of the fats actually go through the lacteal. We'll talk about that later in the digest-subtract. And actually, the lymphatic system. But it allows a lot of things to go through. Now, this allows the most. So we're going to find this in the spleen because this is the graveyard of red blood cells. Even red blood cells can go through here. Look at that. This red blood cell can sneak through somebody's hole. And you're going to find it in the liver. You're going to find it in bone marrow. Why? Because we're making red blood cells. This is our chance to pick them up, right? And so... Again, a sinusoidal capillary. The blood flow is slower. It allows some time for things to go through. Contains macrophages. Why? Again, destroys foreign invaders. And the spleen is the graveyard for red blood cells after they lived too long, say 90, 100, 110, 120 days. And a capillary bed, as we said, is a big extension. And basically... a lot of exits and a lot of collateral capillaries that red blood cells and the blood can go through. It goes a little bit slower, and it allows for the gas exchanges. So it says there's two different types of vessels here. The vascular shunt, remember the thoroughfare channel we talked about, they call that a metarterial, but also a true capillary. And this is the one that has the gas exchanges. So we talked about the metarterial having these shunts. and I call them precapillary sphincters. They don't talk about that here. But the precapillary sphincters are a little smooth muscle around it, and it squeezes, and it does not allow some blood. It doesn't allow a whole lot of blood to go through. And so basically it can bypass that area. So, again, this is a shunt. For guts, for instance, blood comes in, you have a fight-or-flight response, and blood is shunted to the skeletal muscle so you could run and fight. and flee and kind of thing. The thoroughfare channel is the one that allows it to bypass, bypass. So here we see it. We see the vein, or sorry, artery coming in. Here's the pre-capillary sphincters. Blood will go through, and this is the whole capillary bed. But again, if we squeeze all these, they're off our channel, my arterial, which is a shunt, shunts it past. But this is where gas exchange is happening. This is where absorption of nutrients is happening. This is where all the magic happens. But we can bypass it. Oopsie. Oh, gosh. There we go. And so how many are there? How many different vessels are leaving it? Up to 100. That's a lot. And here's where you're talking about the precapillary sphincters. They squeeze. They don't allow blood to go through. But this is where the filtration happens here. And this is bypassing the whole thing. And so veins. Now remember, it goes from a venule first, capillary first to a venule, because the venules are smaller. And it's very porous. So it allows you to suck up the fluids. What do you mean suck up the fluids? Well, look right here. There's a lot of fluids. dumping out fluids, dumping out fluids, dumping out fluids. Now the capillary side of the veins, they're going to pick up some, but the venules will too. And they're just, they allow stuff that gets sucked in easily. So it can pick up a lot of stuff. So it's very porous. Again, allowing the fluids and red bloods, I'm sure white blood cells into the venules, not only into tissues, but sucking it up basically from, I should say from tissues instead of into. This is more of an arterial, is into the tissue. This should say from the tissues. I think they have that wrong. This is sucking it up and bringing it back to the heart. It shouldn't be into tissue, but from. So the large venules start to have some smooth muscle, and then when it gets to the vein, then we get to the when we valve. So the veins have two mix. Again, those are three layers of intima, media, and externa. But the media is thin here. Remember, it's not as thick as an artery. Not as thick as an artery. The external is thicker, and we have vein. Where is the, you should talk about a valve here somewhere. Large lung. Anyway, oh, storage vessel. Remember I said that veins hold more blood than arteries do? If you had a cut, and you cut an artery, and remember, arteries are high pressure. Veins are low. pressure. So if you cut an artery and an artery is where you carry all your blood, it says right here, 65% of blood supply in the veins. If you had 65% of your blood supply in an artery and you get cut and you have high blood pressure, you're going to, you're going to explode. Somebody cuts you, you're going to pop like a zit and you're splashed the whole room. It's going to be a giant splash and you're dead. But in a vein, it's low pressure. So you might, you know, if you cut an artery, you still squirt blood across the room, but you don't giant splash. In a vein, there's low pressure, so it holds the reservoir so that you can stay alive. And it's under low pressure, so you're not just going to explode and pop and splash it everywhere as much, right? Low pressure. Can you bleed out? Absolutely. But it's less of a chance. So here we see an artery in a vein. Now, the vein, I said, has a larger lumen. Well, this is like bread. It got squished when I cut it. You know what I mean? They're putting it on a slide. It's the way it looks. Veins always squish because they have a thinner wall. Because their wall is thinner, they actually have a larger lumen. If we open this whole thing up, it would be bigger than an artery. Arteries have more muscle, more muscle, more muscle, more muscle. Tunica media, tunica media, right there, look at that. Where's the tunica media? Thin, okay? So thinner tunica media on a vein. But the outside, tunica externa, quite thick, pretty impressive, right? But they have a larger lumen. Capitulant vessels. On the test, always, always, always ask this kind of thing. Which one holds more? Blood, it's all veins. Look at this. Look at that. 60% to 65% of all the blood is stored in veins and venules. Arteries and arterioles, only 15%. Otherwise, again, giant splash. Pulmonary, blood vessels, 12%. Heart, only eight. Capillaries, five. Look at that. Everything's in the vein. Okay. So blood pressure, of course, it's lower than an artery. Again, before it hits the heart, it almost falls. into the right atrium. It's about zero is the pressure when it gets ready to fall into the right atrium. So the valves, these prevent backflow. They're one way. They're most abundant in limbs, for example, arms and legs. And so it's a long, that's quite a long distance. I'm six foot three. That's a long distance to push blood from your lower leg up to your thorax. And so your muscle movements push it and they don't back up. And venous sinuses, it says flattened veins with extremely thin walls. It's only epithelium. But the coronary sinuses, the heart and the dural sinuses of the brain are these. So coronary sinuses, why are they flat? Because during contraction, you don't want them to pop, right? They have to be empty. And so we'll talk more about that when we talk. Well, actually, I think that's about it. So sinuses of the brain and the coronary sinuses of the heart, that's about the only time we're going to mention them. All right. Again, there's your picture. You know, I don't think I talked about the capillary down there. Back up. The capillary down there, simple squamous epithelium and a basement membrane. We saw this earlier. We saw this earlier. And varicose veins, I talked about this, is a leaky, incompetent valve. They get there. They can hurt. It's pushing blood down and backwards, and your body sure doesn't like it. And where do we see that? Anytime you gain a lot of weight, anytime you this is one you won't hear anywhere. If you walk on concrete a lot, people that stand on concrete a lot have a much higher incidence of varicose veins. Pregnancies can do that. Just standing for long periods of time in one position, sitting in periods of time for one position. So long car rides, plane rides can also help increase your chance of having a blood clot and varicose veins. So keep that one in your back pocket and knowledge. Pregnancy is... absolutely horrible on the human body. I said the word horrible. I shouldn't say. It's hard. It's hard on the human body. But if you ask somebody that's pregnant with like twins or triplets, it's so hard on their body. It just does things to you. And so weakening the valves affecting more than 15% of people, guys, gals, a little bit of everybody there. And they hurt. So how do they treat them? At these varicose vein clinics, sometimes they'll take them out. Sometimes they will inject them with like a salt type of solution to help pull water out. But basically, there's a whole bunch of different things that are new in the treatment plans that I haven't heard about. But that's the old school. It's done in the last 10 years. So again, straining to deliver a baby, having bowel movements can increase inter-abdominal pressure. It can give hemorrhoids. Basically, the veins there at the very bottom of the rectum. We haven't covered the digestive tract yet, but that's one. Okay, so vascular anastomosis. This is interesting. Listen to this. There's been people that they think have heart attacks, probably did, and they take them in to do heart surgery to do a bypass, and they found that the human body already grew an artery around it, basically. and it gave a new blood supply. And so this is a collateral channel. It's an alternate pathway to help prevent, you know, blocking. And so if one artery is blocked, it will grow around it. We sit in joints a lot, sometimes in the heart, brain for sure. So AV. arterial venous anastomosis. This is a shunt. We talked about the thoroughfare. That's what that is. And venous anastomosis is so abundant, so abundant that you almost never hear veins being blocked. The only time I hear about this? Surgery. That's because they cut them, took them out, screwed them up. Let's talk about more of the physiology of circulation, how blood flows. This gets a little bit more complex.

If it gets too low, people feel kind of faint. If it's too high also, it can cause damage to the kidneys because of the amount of pressure just... pushing on the glomeruli. But how do we determine if this is a good or bad thing?

A lot of people will just say, I feel fine. There's nothing wrong with me, except that high blood pressure is the silent killer. People don't really experience that much discomfort except possibly headaches with high blood pressure. And so you really don't realize that you have it. I've probably had 50, 60, 70 patients.

that had high blood pressure and did not even know it. Probably had 10 patients over the last 10 years that have diabetes that didn't even know it. But high blood pressure is very common and nobody really notices anything. Therefore, it's a silent killer.

And so, neat little video to watch there. When you look at blood vessels, when they leave the heart, anything leaving the heart is considered an artery. Anything returning blood to the heart It's considered a vein and the capillaries in the middle are basically your direct contact with tissue cells because they're the smallest.

They're so small that basically every cell in your human body is near one to where it can get the nutrient supply from it. Now, between arteries and capillaries, it's a big jump from a big artery to a little bitty capillary. So there are arterioles in between them. And then from a capillary to vein is a big jump. So there's a venule in between those.

And we'll be seeing more of those in a little bit. But remember, the heart is basically sending blood out. It gets smaller, smaller, smaller until it becomes an arteriole.

And then it goes to these capillary beds. Now, capillary beds are basically many, many, many little branches of vessels that are going here throughout a muscle. It could be a calf muscle or a toe, for example. And. Now, the interesting thing about this is that there are, let's change this.

Let's change this to a stomach area. Let's go even intestines. Now, this is easier to kind of describe to you guys for one reason. Is it important to digest a peanut butter jelly sandwich when someone's trying to kill you? Are you getting vandalized, mugged, whatever?

Running from a tiger? I don't know. Whatever causes your fight or flight response. Is it important to digest food at that point?

And the answer is no. Basically, we shunt blood away from the digestive tract and put it towards skeletal muscles. So you can fight, so you can run, so you can do whatever you need to do.

And so we have these little things here called precapillary sphincters. These precapillary sphincters can squeeze and basically prevent blood from going through them. And if it does that, well, blood will simply bypass the capillary bed and continue on its way back to the heart. And so this whole area can get skipped.

And that's called a thoroughfare channel. And I always give the example of, I'm sorry, I'm choking on nothing. So I'm going to get me a drink here. But the Lloyd Expressway is a thoroughfare channel. It's like one of the major channels where traffic is running through Evansville.

But if you closed all the exits, where would you end up? Gateway Hospital is on the opposite side of Vandenberg County heading. from USI East. So you would bypass the entire city of Evansville. Well, this is very similar.

If they're putting a gate up to where you can't exit the Lode Expressway, you can't go into the city. So you would simply go all the way around. And so these are thoroughfare channels and bypassing by pre-capillary sphincters.

Now, capillary beds are very wide and there's many of them. So when a blood's coming through here, it's going kind of fast. So it goes pretty quick down through. thoroughfare channel.

But if we were going to capillary bed, it slows down because there's so many of these. The blood can slow down. And then we have gas exchanges of oxygen, carbon dioxide, so on and so forth.

And so again, it's slowing down because of gas exchange. Now, we also see a couple of things in here. Sinusoids, we'll talk about in a little bit, but lymphatic capillaries. The reason we have these lymphatics, and we'll talk about those here in the next chapter, is that not all of the plasma coming in and going into the intercellular spaces or between the cells.

interstitial fluids is what they will become. Not all of it is getting sucked back up by the vein. And that's because here it comes in at a great pressure, but it leaves as a low pressure. Some of it's left behind.

And so the capillary from the lymphatics are going to suck up that extra juice. So then we go venule, vein, and back to the heart. Now, the interesting thing about a vein is nothing's pushing them. You're like, what are you talking about, Vandal?

Well, here on this side, the heart is pushing the blood this way. So what? is pushing the blood back. Is it just simply the flow coming down and continuing to push it?

Not necessarily. If it comes too high of a blood pressure, this might just put extra, you know, fluids in your leg and you'll end up with swelling. So what is pushing it back to the heart? And the answer is a couple things.

One is there's a little bit of a smooth muscle in the wall. The other is that There is a one-way valve in veins, and so when blood goes so far, it can't back up. And the other is when you squeeze your muscles, like, say, your leg or your arm, you put pressure against it, and it pushes blood to the next area, and it can't back up. And you move your leg again, and it pushes blood a little bit farther, and it can't back up.

And you breathe, and it pushes blood a little bit because your guts, you know, and things squish against it and keeps pushing. So right up here, the pressure is extremely low, almost zero. But here, it's whatever your blood pressure is, like, say, 110 over 80. That's the 110 or 120 or whatever your blood pressure is.

Let's go to the next. So the blood vessels are all made up of a total, at least not all made up of it, but all of them have the ability to have all three of these layers. So they're called tunics instead of layer. So intima means inside or intimate, most intimate inside of the blood vessel.

The media is very similar to a heart like myocardium is a muscle. So in the tunica media here, we're going to have smooth muscle and tunica externa, external. So it's the outside.

That's pretty easy. Now, when you get down the capillaries, you might only get up to this, just the tunica intima, because one layer of simple squamous epithelium is about all the thick that the capillary is. So in the tunica intima, this is the simple squamous epithelium.

And the reason that's cool is because this slick surface reduces friction. It's the same exact surface we see in the heart. We talked about inside the heart how it's slick and how blood doesn't see the collagen, and therefore it doesn't have the clotting cascade, the coagulation cascade of fibrinogen changing to fibrin and the platelets becoming sticky.

So that's the same as blood vessels. All the way through, it has this simple squamous haptothelium that was basically keeping that slick lining. The same as endocardium.

Exact same stuff. It just keeps on flowing all the way through. The connective tissue basement membrane. Well, the simple squamous epithelium has to be connected to something. And so we have some basement membrane there, but it says vessels larger than one millimeter.

And so it can get so small. It's just one simple squamous epithelium. Tunica media. This is the smooth muscle inside.

Time for some Gatorade. Smooth muscle inside. Now, the interesting thing about smooth muscle is it contracts, right?

So as it contracts, it squeezes. Now as I picked up my Gatorade bottle, which I love orange Gatorade, if I take this Gatorade, and I know you can't see it, but you can envision a Gatorade bottle or a water bottle, and you put the lid on, all right, you get the lid on, and you squeeze the bottle. Now, did pressure go up or did pressure go down?

My Gatorade bottle, the pressure went up. Let's talk about the inside lumen, and there was a space inside. When I squeeze this Gatorade bottle, What happens to the inside diameter?

A gain goes down. That's why it squeezes on the Gatorade, and that's why pressure goes up. Remember, pressure and volume are inversely proportional, because as I squeeze the Gatorade bottle, the volume went down, pressure went up.

But if I were to let go and vasodilation, the vessel gets bigger, the diameter increases, which means volume goes up, pressure goes down. That's an important thing to remember. Gosh, Gatorade sure is good. So, the bulcus layer responsible for maintaining blood flow and blood pressure is where the smooth muscle is. Smooth muscle, tunica media.

Now, tunica outside, externa, is basically connective tissue to where everything, basically just holding everything together. So, here, composed mostly of loose collagen fibers that protect the wall. and anchor it to surrounding things. That makes sense.

Now, it can have nerves. So if you cut a blood vessel, it can hurt. Because it has nerves. The blood vessel, as we said before on this slide right here, media, that's muscle, ladies and gentlemen.

It needs blood. So the tunica externa has to have some sort of a blood vessel called vasovasorum, which is the network of blood vessels feeding and nourishing the outside layer and a lot of times the myocardium. Why did I say myocardium?

I meant tunica media. Sorry, sorry, sorry about that. So here's the, I don't know what word I just made up there. It's late at night.

The vasovasorum here is the blood vessels, and then the yellow is supposed to be the nerves, and this gives blood to here. We have the tunica media, which blood can go in. We have some elastic fibers versus muscle because there's different types of, let me back up.

I'm sorry, I must have missed that. But there's different types of, here it is, different types of arteries. For example, elastic and muscular.

The reason that this is elastic up here in the aorta is does the aorta have to contract at all? The answer is no, it does not. The aorta never really contracts.

It rebounds. It's basically a huge rubber band tube. If you push a bunch of blood in there, it snaps back. It does not.

It simply does not. have to squeeze at all. It just snaps back and that's its main purpose.

So it's more elastic. But if you get farther down the body, there's a lot of smooth muscle to squeeze to help push and maintain blood pressure. Back to this one. Why is there elastic membranes?

And the answer to that is sometimes it needs a recoil back, like we said, and in the muscle itself. Now, here's a picture of an artery. Here's a picture of a vein.

Now, if you put them side by side, they're about the same size. You're like, no, it isn't. This lumen's bigger. This must be fatter. There's much more muscle.

Yeah, but overall, the size is about the same. The outside is about the same. There's more muscle in the artery.

There's less muscle in the vein. There is a smaller hole in the artery than the vein. You're thinking it's about the same.

You're going to have to trust me that veins have a larger lumen than... arteries do veins carry more blood in them than arteries do you're gonna have to trust me we'll come back to it and what do we have here valve so this is a one-way valve blood goes one way and when it tries to back up this valve pushes open but it can't back up so the blood gets pushed from here now there's something that can go wrong if the pressure is too high And these valves maybe get older because we age. They become a little bit more incompetent. And blood pools and kind of pushes back. And so that can cause a swelling.

It can cause something called a, and you know what? I can't believe I forgot the name of it. Varicose.

That's a varicose vein. So varicose veins are basically the valves. Not allowing the blood to go through and having trouble backing up. All right, so here we have elastic arteries.

Now remember, its job is to bounce back. And where do we find it? Up there in the aorta. Anyway, so it has a lot more elastic tissue than smooth muscle.

But the muscular one, right here, not as much elastic, but much more smooth muscle. And then arterial, as it gets smaller, they lose both. Why do they have less?

Because it's getting littler. It's getting smaller. So it's going to have less muscle. When you get down to capillary. okay well even arterial and a smaller arterial and there I don't know why I had archer there it's a capillary okay so this is a capillary and look at this no elastic tissue no smooth muscle no fibers it's just simple squamous epithelium that's all it is one layer of simple squamous epithelium and it's basement membrane holding it together On a venule, you see it gets a little bit more of the muscle back, and it has some fibrous layer back.

Vein has a little bit of everything again, except much less muscle on a vein than on an artery, especially a muscular artery. It's almost the same as an elastic artery, volume-wise, but there's much more elastic tissue. So veins, as you see, look more like an arterial, but they have a whole lot more.

As far as muscle, they have a whole lot more fibers connected to show me outside so again on arteries There's elastic, as we talked about. There's muscular and then smaller arterioles. The elastic, it says aorta and major branches.

Again, its job is to bounce back like a rubber band. This huge bolus of blood gets pushed out of the heart, and it's basically a wave. And as it snaps back, it continues to push the blood forward. So it doesn't do a whole lot of... work except stretch and bounce back.

The elastic tissues found in all three layers, the internal, the tunic internal, the tunic external, and the tunic media, but mostly in the media. All right, so they act as a pressure reservoir that expands and recoils. Rub band, ladies and gentlemen, allows for continuous flow downstream. In other words, it expands and then it contracts and pushes that blood along. Muscular arteries.

Now, so we have less elastic tissue, more muscle. And so because there's more muscle, this is where the true vasodilation and vasoconstriction events happen. Now, it says, look at this, diameters range from pinky finger size.

That's not a big artery. A pinky finger is a huge artery. Down to pencil lead size.

So definitely they get smaller, smaller, smaller. But it's most of the arteries that are named except for aorta. and abdominal aorta and descending aorta, all the rest, mostly are the muscular arteries. It says it has thickest tunica media, and obviously because all the muscle, but not as much elastic tissue.

And so the active for, again, muscle squeezing, vasoconstriction. You can squeeze blood vessels, and the pressure goes up. It helps propel blood arterioles. They're just getting smaller on the way.

We don't name all the arterioles. They just get smaller, smaller, smaller. They have less muscle.

They have less elastic tissue. They're called resistance arteries because the changing diameters change the blood pressure. Sorry, change the resistance to blood flow. Let's talk about resistance. It says the changing diameter changes resistance.

Well, anybody that has ever used any kind of a pipe or any kind of a garden hose, knows a couple things about resistance and that is the longer it is the less flow the the skinnier it is the less flow so a big fat pipe has more flow in fact size diameter is the number one thing that changes resistance i'm going to say that again diameter is the number one factor changing resistance if you have a pipe and you double the size you're way more than double in the full you're way more than halving the resistance it goes to i think it's an eighth or a sixteenth it goes down considerably in in uh in change in diameter and they lead to capillary beds which of course we saw as the capillaries so let's talk about them they're microscopic they're itty bitty these things are so small that a red blood cell has to fold in half it says not only pass through i'm telling you the real truth is some of them have to fold in half to get through because it's so tight. So the wall, it says walls, just thin tunica intima. Walls are just a thin tunica intima.

In the smallest vessels, one cell, one cell forms the entire circumference. It's very tight. And so how little is that?

Let's think about this. If you've got pencil, the mechanical pencils, point, it's point 80, the itty bitty ones, the ultra fine ones. Very, very, very small.

So parasites. I've never asked this, honestly. Spider-shaped stem cell helps to...

I've never asked that, ever. Probably never will. Don't worry about that. Supplies almost every cell except for cartilage. Now, what are we talking about?

Okay, I got to tell you. Highland cartilage. Highland cartilage does not have a good blood supply. That's why it wears down. If you wear out a disc or cartilage between bones, It's not going to grow back.

You're just S-O-L. It's not going to grow back. I mean, you could take shark cartilage. You could take MSM.

You could take all kinds of herbal stuff. And it will decrease the pain. And honestly, the best thing you can take is hyaluronic acid. We'll talk about that some other time. But you can't get that cartilage back.

Epithelium has an okay blood supply because it comes through the basement membrane. The corner of your eye and the lens of your eye. Horrible blood supply.

The cornea can be transplanted with almost no chance of rejection by the immune system because there's no blood supply, therefore almost no immune system. So the function of a capillary is it brings oxygen to the tissues, right? It brings nutrients.

What do I mean nutrients? Glucose, amino acids. It brings, you know, sodium chloride, all these different things.

But it also brings waste products and removes waste products. So more removing waste products. Hormones, as we talked about in the endocrine chapter, we're bringing the hormones to the cells and the blood. Between blood and interstitial fluids, between blood and interstitial fluid.

What are they saying here? Oh, they're saying the capillary is the thing between the blood and the interstitial fluid. So blood comes in down through the capillary.

It leaves through the wall, and now it's an interstitial fluid. So what is the difference here again? Blood and interstitial fluid.

What is the difference? Blood is basically all the way. We know what blood is. It's got all the formed elements and such. But what is interstitial fluid?

Okay. Interstitial fluid does not have proteins. And it does not have the red blood cells. Mostly it's plasma getting pushed out, but we don't call it plasma anymore.

And it's nutrients and things, but we don't call it that anymore. We call it interstitial fluid. So capillaries, there's three different types. Continuous capillaries.

It all depends on how big a hole there is for things to get through. Medicine does not allow much through. It says abundant in skin, muscles, lungs, and central nervous system.

But in the central nervous system, there's a blood-brain barrier. And remember, these are foot cells of astrocytes that are basically causing the blood-brain barrier. But they're enclosing it with a very tight junction.

And so a lot of stuff doesn't get through. And when we talked about brain, if you had my class, we talked about amino acids and some things. If they're allowed to pass through the brain, they act as neurotransmitters.

And they're hyper-excite neurons and kill neurons. Horrible stuff. So continuous capillaries, we have basically the blood coming through.

And it's more of a tighter junction. These are tighter junctions. I don't know what terms they use. What's it say? I don't want to say much.

But it's more of a tighter junction. Oh, it does say that. Total enclosed is a tight junction.

Well, what do you know? My exact words. But they don't allow much to go through.

They definitely filter much less. Now, this fensterated, and by the way, that is the typical capillary throughout the body. They don't filter as much. But a fenstrate, it looks like somebody came along and drilled holes in it. And this is what you find in a kidney.

This is what you find in a kidney. And it allows a lot of plasma to go through. And it allows glucose and pretty much everything to go through except, again, no proteins, no red blood cells. But it allows pretty much everything else to go through.

So definitely increased permeability. These fenstrations, it says, covered with a thin glycoprotein diaphragm. Look at this. It looks like somebody drilled a bunch of holes into this capillary, and so more filtration. But there's another, and again, you're going to find it's a myelomeralis.

It's typically what you're going to find in the kidney. We'll talk about the kidney in a different chapter. Some digestive organs have this because we're increasing nutrients, so you can bring the amino acids and things back to the liver, fats and such.

But most of the fats actually go through the lacteal. We'll talk about that later in the digest-subtract. And actually, the lymphatic system.

But it allows a lot of things to go through. Now, this allows the most. So we're going to find this in the spleen because this is the graveyard of red blood cells.

Even red blood cells can go through here. Look at that. This red blood cell can sneak through somebody's hole.

And you're going to find it in the liver. You're going to find it in bone marrow. Why?

Because we're making red blood cells. This is our chance to pick them up, right? And so... Again, a sinusoidal capillary. The blood flow is slower.

It allows some time for things to go through. Contains macrophages. Why?

Again, destroys foreign invaders. And the spleen is the graveyard for red blood cells after they lived too long, say 90, 100, 110, 120 days. And a capillary bed, as we said, is a big extension.

And basically... a lot of exits and a lot of collateral capillaries that red blood cells and the blood can go through. It goes a little bit slower, and it allows for the gas exchanges. So it says there's two different types of vessels here. The vascular shunt, remember the thoroughfare channel we talked about, they call that a metarterial, but also a true capillary.

And this is the one that has the gas exchanges. So we talked about the metarterial having these shunts. and I call them precapillary sphincters.

They don't talk about that here. But the precapillary sphincters are a little smooth muscle around it, and it squeezes, and it does not allow some blood. It doesn't allow a whole lot of blood to go through.

And so basically it can bypass that area. So, again, this is a shunt. For guts, for instance, blood comes in, you have a fight-or-flight response, and blood is shunted to the skeletal muscle so you could run and fight.

and flee and kind of thing. The thoroughfare channel is the one that allows it to bypass, bypass. So here we see it. We see the vein, or sorry, artery coming in. Here's the pre-capillary sphincters.

Blood will go through, and this is the whole capillary bed. But again, if we squeeze all these, they're off our channel, my arterial, which is a shunt, shunts it past. But this is where gas exchange is happening. This is where absorption of nutrients is happening.

This is where all the magic happens. But we can bypass it. Oopsie.

Oh, gosh. There we go. And so how many are there?

How many different vessels are leaving it? Up to 100. That's a lot. And here's where you're talking about the precapillary sphincters.

They squeeze. They don't allow blood to go through. But this is where the filtration happens here.

And this is bypassing the whole thing. And so veins. Now remember, it goes from a venule first, capillary first to a venule, because the venules are smaller. And it's very porous. So it allows you to suck up the fluids.

What do you mean suck up the fluids? Well, look right here. There's a lot of fluids. dumping out fluids, dumping out fluids, dumping out fluids. Now the capillary side of the veins, they're going to pick up some, but the venules will too.

And they're just, they allow stuff that gets sucked in easily. So it can pick up a lot of stuff. So it's very porous.

Again, allowing the fluids and red bloods, I'm sure white blood cells into the venules, not only into tissues, but sucking it up basically from, I should say from tissues instead of into. This is more of an arterial, is into the tissue. This should say from the tissues.

I think they have that wrong. This is sucking it up and bringing it back to the heart. It shouldn't be into tissue, but from.

So the large venules start to have some smooth muscle, and then when it gets to the vein, then we get to the when we valve. So the veins have two mix. Again, those are three layers of intima, media, and externa.

But the media is thin here. Remember, it's not as thick as an artery. Not as thick as an artery.

The external is thicker, and we have vein. Where is the, you should talk about a valve here somewhere. Large lung. Anyway, oh, storage vessel. Remember I said that veins hold more blood than arteries do?

If you had a cut, and you cut an artery, and remember, arteries are high pressure. Veins are low. pressure.

So if you cut an artery and an artery is where you carry all your blood, it says right here, 65% of blood supply in the veins. If you had 65% of your blood supply in an artery and you get cut and you have high blood pressure, you're going to, you're going to explode. Somebody cuts you, you're going to pop like a zit and you're splashed the whole room.

It's going to be a giant splash and you're dead. But in a vein, it's low pressure. So you might, you know, if you cut an artery, you still squirt blood across the room, but you don't giant splash. In a vein, there's low pressure, so it holds the reservoir so that you can stay alive. And it's under low pressure, so you're not just going to explode and pop and splash it everywhere as much, right?

Low pressure. Can you bleed out? Absolutely.

But it's less of a chance. So here we see an artery in a vein. Now, the vein, I said, has a larger lumen.

Well, this is like bread. It got squished when I cut it. You know what I mean?

They're putting it on a slide. It's the way it looks. Veins always squish because they have a thinner wall. Because their wall is thinner, they actually have a larger lumen.

If we open this whole thing up, it would be bigger than an artery. Arteries have more muscle, more muscle, more muscle, more muscle. Tunica media, tunica media, right there, look at that. Where's the tunica media? Thin, okay?

So thinner tunica media on a vein. But the outside, tunica externa, quite thick, pretty impressive, right? But they have a larger lumen. Capitulant vessels. On the test, always, always, always ask this kind of thing.

Which one holds more? Blood, it's all veins. Look at this.

Look at that. 60% to 65% of all the blood is stored in veins and venules. Arteries and arterioles, only 15%. Otherwise, again, giant splash.

Pulmonary, blood vessels, 12%. Heart, only eight. Capillaries, five.

Look at that. Everything's in the vein. Okay.

So blood pressure, of course, it's lower than an artery. Again, before it hits the heart, it almost falls. into the right atrium. It's about zero is the pressure when it gets ready to fall into the right atrium.

So the valves, these prevent backflow. They're one way. They're most abundant in limbs, for example, arms and legs. And so it's a long, that's quite a long distance. I'm six foot three.

That's a long distance to push blood from your lower leg up to your thorax. And so your muscle movements push it and they don't back up. And venous sinuses, it says flattened veins with extremely thin walls.

It's only epithelium. But the coronary sinuses, the heart and the dural sinuses of the brain are these. So coronary sinuses, why are they flat?

Because during contraction, you don't want them to pop, right? They have to be empty. And so we'll talk more about that when we talk.

Well, actually, I think that's about it. So sinuses of the brain and the coronary sinuses of the heart, that's about the only time we're going to mention them. All right. Again, there's your picture. You know, I don't think I talked about the capillary down there.

Back up. The capillary down there, simple squamous epithelium and a basement membrane. We saw this earlier.

We saw this earlier. And varicose veins, I talked about this, is a leaky, incompetent valve. They get there.

They can hurt. It's pushing blood down and backwards, and your body sure doesn't like it. And where do we see that?

Anytime you gain a lot of weight, anytime you this is one you won't hear anywhere. If you walk on concrete a lot, people that stand on concrete a lot have a much higher incidence of varicose veins. Pregnancies can do that.

Just standing for long periods of time in one position, sitting in periods of time for one position. So long car rides, plane rides can also help increase your chance of having a blood clot and varicose veins. So keep that one in your back pocket and knowledge. Pregnancy is... absolutely horrible on the human body.

I said the word horrible. I shouldn't say. It's hard.

It's hard on the human body. But if you ask somebody that's pregnant with like twins or triplets, it's so hard on their body. It just does things to you.

And so weakening the valves affecting more than 15% of people, guys, gals, a little bit of everybody there. And they hurt. So how do they treat them?

At these varicose vein clinics, sometimes they'll take them out. Sometimes they will inject them with like a salt type of solution to help pull water out. But basically, there's a whole bunch of different things that are new in the treatment plans that I haven't heard about. But that's the old school. It's done in the last 10 years.

So again, straining to deliver a baby, having bowel movements can increase inter-abdominal pressure. It can give hemorrhoids. Basically, the veins there at the very bottom of the rectum.

We haven't covered the digestive tract yet, but that's one. Okay, so vascular anastomosis. This is interesting. Listen to this.

There's been people that they think have heart attacks, probably did, and they take them in to do heart surgery to do a bypass, and they found that the human body already grew an artery around it, basically. and it gave a new blood supply. And so this is a collateral channel.

It's an alternate pathway to help prevent, you know, blocking. And so if one artery is blocked, it will grow around it. We sit in joints a lot, sometimes in the heart, brain for sure. So AV.

arterial venous anastomosis. This is a shunt. We talked about the thoroughfare.

That's what that is. And venous anastomosis is so abundant, so abundant that you almost never hear veins being blocked. The only time I hear about this? Surgery. That's because they cut them, took them out, screwed them up.

Let's talk about more of the physiology of circulation, how blood flows. This gets a little bit more complex.

Transcript for:Understanding Blood Vessels and Pressure

Transcript for:
Understanding Blood Vessels and Pressure