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Studying for a test? Prepare with these 12 lessons on Advanced circulatory system physiology.
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I'm going to draw for you two of the most important organs in our body. And actually, on the left and right side of our body, they pretty much look like that, like little kidney beans. And in fact, that's what they are. They're kidneys. And so we have some arteries, the renal arteries that flow into them. And renal is just another word referring to kidneys, and we've got renal veins with blood flowing back out of them. So once the blood is headed back to the heart, we call it a renal vein. And there are two of them. And probably the most important part about these kidneys, certainly the thing that makes them really unique, is that they have these ureters. And these ureters drain urine into a bladder. And actually, I'll draw that right here. That's the bladder. And the ureters are the third tube coming out of our kidneys. And then when you're ready to urinate, you can release all that urine from your bladder into the outside world. And so there are three basic things that I want you remember coming into and out of kidneys-- the renal arteries and the renal veins and the ureter. Now, to really make sense of it, you've got to think about how the artery might split up. So let's say we go back to the artery and you follow it, and it starts kind of branching. Let's say it makes five little branches. And then it might have more branches off of those branches and finally maybe even some more branches, and eventually it's not even an artery anymore. Right? All these little branches are so tiny, you would call them arterioles. And let's just take this arteriole, this little guy, and let's see what happens. So let's say I take that little guy and show you on the left side of the screen what that would look like. So let's take a look at this arteriole a little bit closer. So this is our Afferent arteriole, A capitalized. And it's called Afferent because it's headed toward something. Afferent arteriole. And let's not forget where it comes from. It's coming from the renal artery headed towards something, and that something is this. The artery-- or the arteriole, rather, starts making a lot of little turn-backs on itself and finally straightens out. And when it does we call it the Efferent arteriole. So that's how we keep straight whether it's coming or going from this little network, if you want to call it that, of blood vessels. And in fact, this little network of blood vessels, if you look under a microscope, is actually being hugged by something like this. This is actually really interesting. This is the first time we're taking a look at something that is not a blood vessel in the kidney, and it begins our journey of urine. So this thing is called the Bowman's capsule. This is the thing in yellow that I've drawn for you. And whenever things are named like this, you've got to wonder, who was Mr. Bowman? And Mr. Bowman, turns out, was from England. Actually, he was a very curious fellow. And so he looked under a microscope. And he noticed that if you look right where these little tufts of blood vessels are, you can actually see that there's something surrounding each of them. And so he called that Bowman's capsule, and so that's what we still call it today. So England was laying claim to parts of the kidney anatomy. You may not even have known that. So that's Bowman's capsule, and that's the first part of the nephron. I'll actually show you all the parts of the nephron. So the next part of the nephron-- and nephron just means kind of the unit of the kidney that we care about. The next part is looking really squiggly, very convoluted. Right? And I'm trying to draw it that way purposefully, because I want to show you a way of remembering that this is actually called the proximal-- because it's near the Bowman's capsule, so it's proximal-- convoluted tubule, because this is one long tubule, like a little tube. And so this is the proximal convoluted tubule. So basically, the next part of the nephron, after it starts in the Bowman's capsule, is the proximal convoluted tubule. And then it gets into kind of a long deep loop, long loop like that. And this loop is called the loop of Henle. So you're seeing now part three is Loop of Henle. Now, loop make sense. But of Henle, you've got to wonder, again, is this another British guy? Who is Mr. Henle? Mr. Henle, it turns out, is actually not British. But he's from another part of Europe. Let's see if you can guess before I finish this drawing. He discovered that if you follow the nephron deep into the middle of the kidney, it has these little loops, very delicate loops, but very important in helping urine form. And he was a German scientist. And so if the British are going to identify something, so will the Germans. And so we still call that the loop of Henle. And after the Loop of Henle, we have another area that's very convoluted. And so you can guess what we call this where, because we're going to probably try to stay consistent. And if the first part was called the proximal convoluted tubule, we would call this not the proximal, because now it's not near anymore, but it's a little further away. We would call this the distal, meaning further away, convoluted, because it's still convoluted, tubule. So this is the distal convoluted tubule. And finally, there's a fifth part of all this. The fifth part of all this is a giant tube of collection. So all this stuff goes into a collecting tube. And I'm actually showing you where all the other distal convoluted tubules might be dumping in as well. Maybe there. And eventually all this stuff is going to go to the same place, which is down to the ureter. So we've seen now how things go to the ureter. You can see how things come from the renal artery. But you're probably still wondering-- oh actually, I didn't label this for you. This is the collecting tube. You're probably still wondering where is the renal vein in all this. I mean, I still drew the Efferent arteriole as being red, and it's got oxygen. So where does the venous blood come from? And the answer is right here. So you basically get red blood or oxygenated blood flowing over all these parts of the tubule. So all the parts of the proximal convoluted tubule, the loop of Henle, the distal convoluted tubule, and the collecting duct all get wonderful blood. And then finally, when all is said and done, it all drains into one thing, one final renal vein. And that's with all of the blood coming together. So this little network is considered-- this little network of capillaries, then, is considered, right here, the peritubular, going around the tubule, tubular capillaries. And that makes sense. Now, you can see the renal artery blood coming in, going in through the Afferent arteriole, then the Efferent arteriole, and then draining back into the peritubular capillaries and finally, the renal vein. And this important structure in yellow that I've drawn has five parts to it, and all five parts coming together are called the nephron. And so this is an important structure, and we'll talk about different parts of the nephron in future videos. But this is an important structure, to at least get a sense for how it looks and what the different parts are called.