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Meet the kidneys!

Created by Raja Narayan.

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Video transcript

Voiceover: Imagine you're in a movie theater. You're watching a really, really long movie. And you've finished your entire bucket of popcorn. You've guzzled down a giant soda and all of a sudden, you have to pee. And to make matters worse, you're watching a movie about a whole bunch of people on a cruise ship that hit an iceberg and so, there's a lot of water in this movie and you freak out because now you have to get up and go to the bathroom. But then that should get you thinking, well, how do my kidneys work? How is it that I can make all this pee that I have got to get rid of? Well in the next few videos, we're gonna talk about how the kidneys work. And I'll give a quick overview here before we delve more into the specifics. As you can see, the kidneys sit right here around your belly button. They're about the size of a fist and you've got two of them. And they sit a little closer to the back, not really in the front. So the kidneys receive blood from the heart. So the heart goes on up here. It's also about the size of a fist. And it pumps blood throughout the body. You know, you get some to your arms, you have some that goes up to your brain, and you have this branch that comes down and it goes towards your legs, as well. Well, what you can kind of see in the picture of the kidneys right here, is that they've got a little vessel right there so sure enough, there's some blood that comes from the heart into the kidneys. Both of your kidneys, then, are going to filter the blood and release urine, which is just a collection of waste products that your body wants to get rid of. And the urine is gonna hang out in your bladder that sits about right here, until it's an appropriate time to go to the bathroom. And that's kind of a broad overview. But let's go into a little more detail about what the kidneys do. So I'm going to draw a box over here. And this box is going to be what the kidneys do. So I'm going to give just a really simplistic overview of what the kidneys do. And then in other videos, we'll go dive deeper into detail. So as I mentioned, each of your kidneys gets an oxygenated blood vessel, or an artery that goes to them. And your arteries hold onto all the things in your blood. This can include things like your nutrients. And so nutrients can be anything from say, your electrolytes like your sodium ions. They can be things like your proteins or your amino acids or even glucose, as well, things that build your carbohydrates. So a lot of things that your body uses as the building blocks, or things that help other structures of your body work. In addition to your nutrients, you've also got oxygen hanging out in your arterial blood. And your arteries also contain waste products. So things your body has made through cellular respiration and all these other processes that we undergo that we don't need anymore, that we want to get rid of. And they can include things like urea and other toxic compounds that we don't want to build up. And at the same time, it can also include extra electrolytes, like sodium that we don't need. Because if we hold onto a lot of sodium chloride, which is just salt, we'll end up having high blood pressure. So our kidneys also help us maintain our blood pressure, as we'll talk about in other videos. So, this just kind of underlines the point that if you have too much of your nutrients, they become waste products. And so, your kidneys help to make sure you don't build too much of this good stuff here. So this is all the stuff you've got hanging out in the artery that's coming over to your kidney, right here. And as you might recall, whenever you have an artery coming into an organ or a part of your body, there should be a vein that takes the blood away from it that's going to return it to the heart. So this is your vein, right here. And so the job of the kidneys then, is to make it so that the nutrients you had in your arterial blood are collected and maintained when we get to the vein. So we want to hold on to our nutrients, right here. So I'll just write "nutrients". And it stands for all the stuff that I gave examples for on the left side here. And the kidneys, like every organ in the body, need oxygen to do well. So you'll have the oxygen go through the kidneys and some of it will make it out. Some of it will be used by the kidneys. Because that's how we can maintain some of the tissue. And so when we get to the other side, where the vein is, we'll have less oxygen. So I'll write it really tiny right here to show that there's much less oxygen in your venous blood than there was in your arterial blood. And finally, the kidneys want to take all the waste products your arterial blood brought to the kidney and hold on to it, make it so that this stuff does not end up in the venous outflow. And by collecting these waste products, the kidneys will effectively produce your urine. Now, you might notice in this picture that I am missing something. What connects the artery to the vein? Well actually what goes on here is part of what makes the kidney so special. And it answers the "how". How is it that the kidneys are able to do this? How is it that the kidneys can help us maintain our nutrients in our body while getting rid of waste into urine? Well, the kidney is special because it's got two capillary beds. I think you might have heard what a capillary is before, alright? A capillary bed is just something that connects the artery and the vein. It's where you can have oxygen flow out. You can have nutrients flow in. So the way I'll draw it is that you've got one capillary bed, right here, connecting your artery to your vein, like that. And you've got another one down here connecting those two. And so these guys work together to deliver oxygen to the kidney's tissue and, at the same time, recollect these nutrients so that the vein can take these nutrients elsewhere in the body for use. And these capillary beds have two fancy names. The first one is called the vasa recta. The vasa recta. And that's mainly to give oxygen to the kidneys. The other set of capillaries are called peritubular capillaries. Peritubular capillaries, and we'll talk way more into detail about these peritubular capillaries. And these are the guys that are mainly going to be responsible for collecting nutrients that our kidneys will filter. And we'll talk more about that process in the next few videos.