[BLANK_AUDIO]. Today, we're going to start thinking about blood pressure in a way that you wouldn't expect. We're going to, look first at the anatomy of the blood vessels. Because you can't really begin to understand blood pressure until you understand how the structure of the blood vessels is really influencing what goes on with blood pressure. So, let me ask you what kinds of blood vessels are you aware of? Steph. >> Arteries and veins. >> Arteries and veins. Do we have any other kind of blood vessels? >> I know there's some really small ones, capillaries. >> Yes, we have capillaries. Natalie? >> We have arterioles and venules. >> Arterioles and venules or venules, yes. Yes. So, altogether there are five different types of blood vessels and they all have something to do with how blood circulates through the body, and it's their structure that determines how they will be able to function, how it maintains circulation. So, if we think about the order that they go in, as blood vessels move away from the heart and then back to the heart, we think about the first blood vessel that carries blood away from the heart as being? Andre? >> The artery? >> Arteries. And then, the next type of blood vessel that the blood encounters is? >> The arterioles? >> Arterioles. And then, what's the next type of blood vessel the blood encounters? >> The capillary. >> Capillaries. And then, we see the blood going into? >> Venules. >> The venules and then from there into? >> The veins. >> Veins and finally the blood returns back to the heart. Okay? So there are, those are the five general types and when we think of the arteries, we always think of them as carrying blood where? >> To the tissues. >> To the tissues, but we think of them as carrying blood? >> Away from the heart. >> Away from the heart, and then when we think of veins or the venules, what are we thinking about them doing? >> Carrying the blood back to the heart. >> They carry blood back to the heart. Excellent. Now what, what do the capillaries do, like generally speaking? Why do we need capillaries? Arteries carry blood out to the capillaries and then what happens out there? >> That's where gas exchange occurs. >> Excellent. That's where gas exchange occurs, and specifically when we talk about gas exchange, what are we talking about, what gasses get exchanged in the capillaries? >> Oxygen goes into the tissues and carbon dioxide goes into the blood. >> Excellent. So, oxygen is going to leave the blood and move into the tissues and then CO2 or carbon dioxide is going to be moving out of the tissues into the blood, right? And so, the blood that gets carried in the veins is often we think of being deoxygenated. We're going to get to the idea of that not always being correct, right. Because what we're talking about when we talk about oxygen moving out of the blood into the tissues, which of the circulations are we talking about? >> Systemic. >> Systemic circulation, exactly. So, we learned when we were studying the heart, we learned that there are two circulations. And now, what we've just described. Arteries carrying blood out to the capillaries. Oxygen leaves the blood in the capillaries. Moves into the tissues. C02 moves from the tissues into the blood. And that blood gets carried back to the heart. That's the systemic circulation. What happens in the pulmonary circulation? We have arteries that carry blood where? Mia? >> They go to the lungs. >> Yes, the, the arteries will carry blood to the lungs and in the capillary beds in the lungs, what happens? Gas exchange but in the lungs, how is the gas exchange look? >> The blood gives off the CO2 that it's been carrying to the lungs for us to breathe out, and then our lungs gives us the oxygen that we need. >> Excellent, so every time we breathe in we breathe in air that has a high oxygen content. And then when we breathe out, the air has a higher CO2 content, right. And so when blood goes through the capillary beds in the lungs, the blood will give off CO2 and it will take on oxygen, right. And so then that blood that's coming back from the lungs, will come back to the heart as oxygenated blood. So, that's the two circulations. Arteries always carry blood away from the heart. Veins always carry blood back to the heart. Gas exchange happens in the capillaries, but the pulmonary circulation has a different function than the systemic circulation and the gas exchange looks different, right. So, on the models that we've been looking at in the lab. If you see an artery and it's red, which circulation is it associated with? >> The systemic. >> The systemic. And if you see an artery that's blue, you know it's associated with the? >> Pulmonary. >> Exactly. Alright. So, that's like getting us off to a start with thinking about, a little bit about the structure and the function of the blood vessels. There are few other things that I want to say because we know that one of the five types of blood vessels is an arterial. So, what happens in the vascular system is that the aorta which is the largest artery leaving the heart in the systemic circulation; the aorta branches into smaller blood vessels, those smaller vessels branch into smaller arteries, branching, branching, branching continues. And every time there's a branching of the arteries, the vessels that branch off of a bigger artery are smaller, right. And automatly, we get to the point where the branches are so small that we call them arterioles, right? That word just means little artery, right? Okay, so we have arteries leaving the heart. They branch and branch repeatedly. Finally the branches are small enough that we have arterioles. And it's arterioles that carry blood into the capillaries, right? Okay, so, then, what happens. The capillaries converge and that's where we see the first of the venous system vessels forming. And what is that first type of venous vessel? >> The venule? >> The venules. And the venules converge and converge and they form larger? >> veins? >> Veins. And ultimately, we have very large veins that carry blood back to the heart, right? Okay, excellent.