by Jason Amores Sumpter
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vasculature is what carries the blood around the body. It's going to be lined with a special type of epithelial tissue we call endothelial IAM, and that's going to line the interior surface of these blood vessels. It actually also lines the interior surface of lymphatic vessels, but we'll talk about those a little later. Now there's basically, like three types of vasculature. You need to know their arteries, which are going to transport blood away from the heart. That's what determines an artery. The direction of blood flow is going away from the heart. Veins transport blood to the heart. Now the reason I emphasize the direction is because it's a common oversimplification that people to say, oh, veins, transport de oxygenated blood and arteries transport oxygenated blood. That's true in the case of systemic circulation. But don't forget, there's also pulmonary circulation. So in the systemic loop, arteries are carrying oxygenated blood. But in the pulmonary loop, the arteries carry de oxygenated blood. Remember, that's, uh, that's gonna be the part where the heart pumps the de oxygenated blood to the lungs. So arteries transporting that now arteries have these elastic walls and, you know, a lot of smooth muscle, and this allows them to change their diameter. Which is going to be important when we talk about blood pressure and as arteries start Thio branch and get smaller as they make their way to the tissues and ultimately to become Cap Hillary's. We call these branches arterials, and they have smooth muscle just like arteries, but they have a smaller diameter, so veins kind of like opposite scenario. Here, they're going to carry de oxygenated blood in the systemic loop, but in the pulmonary loop, they're gonna bring oxygenated blood from the lungs to the heart. Veins carry blood to the heart. When the blood's coming from belongs to the heart, it has oxygen. And because the naming of veins and arteries is about the direction of flow, you know, that's why veins air carrying oxygenated blood there. Now, veins are kind of different from arteries. They don't have all that Aziz much smooth muscle. They have some, but they can compensate for this because they actually will run through skeletal muscles. And we'll talk about the significance of that when we talk about blood pressure. Now, veins also have valves in them. Basically, it's going thio If you know, here's your vein. There is going to basically be thes flaps of tissue and they'll allow flow in one direction, but they'll prevent backflow. And the reason this is so important is because the pressure in veins is lower than in arteries arteries. They're gonna have a lot of pressure coming from the heart to keep the blood moving in the right direction. Veins, not so much because they're gonna be coming after the cap Ilary beds. So in order to ensure that the blood keeps flowing in the right direction, veins have these valves in them now, just like arteries branch into arterials before they, uh, you know, become even smaller and are considered capital areas. At that point, as capital Aries start to converge together, they form what are called venue ALS. So these air going to be like, you know, little veins that air going thio converged together and form veins like the main big veins and of course, venue ALS come from converging cap Hillary's. So what are capillaries? Thes are the, uh these I mean these air, the sites where the magic happens. Really? This is where gas exchanges going. Thio exchange of you know, many types is going to occur between blood and tissues, and they're really small. They're tiny, they actually their walls air Onley, one cell thick, and their diameter is about the size of a red blood cell. So they can basically, as you see here, let through like one red blood cell that time they're super thin. I'm sorry they have a super small diameter, and they're super thin. Thio allow for easy exchange. Now they're in tissues there, found as what are called capillary beds. Basically, it's like a a very branched network of capital Aries that's sort of diffuse through a tissue, and this helps maximize surface area in exchange. Now, because capital Aries don't have smooth muscle because they lack smooth muscle, they can't control blood flow like veins and arteries can. They can't constrict and dilate. However, there are what are called pre cap Ilary sphincters, basically ah, little sphincter muscles that will control blood flow into the capillary bed. So this is sort of a capillaries way of compensating and being able to have some control over blood flow. And again it's through these pre cap Larry sphincters that will control the blood that's moving into the capillary beds. So looking at our diagram here, tracing our loops again, we have the heart. And this here, remember, is, um, artery. Sorry, because it's going. It's blood is going away from the heart. So that is an artery, and this is a vain because it's going to the heart. These are arteries, and they're gonna branch, as you can see here and turn into arterials or be considered arterials. And when they get to the tissue, they're going thio become super branched and diffuse and form a cap Ilary bed. It sounds comfortable, doesn't it? Cap. Hillary bed could take a nap there. Now capillary beds are the capillaries in a capillary bed are going to converge and form vein. You ALS and those will converge and form veins. Those veins will lead back to the heart, so that is the basic rundown of the vasculature. With that, let's flip the page