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Meet the kidneys!

The kidneys play a vital role in filtering blood and producing urine. Understand how these fist-sized organs receive oxygenated blood, hold onto essential nutrients, and expel waste products. Discover the unique dual capillary system, the vasa recta and peritubular capillaries, that make this process possible. Created by Raja Narayan.

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  • blobby green style avatar for user mindybo1112
    If kidney filters the blood what happens if it doesnt
    (5 votes)
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  • female robot grace style avatar for user Anna
    the bladder does sit in front of the uterus in females and intestines and aorta in everybody so wouldn't it be more efficient if our kidneys were in front of our stomach and liver?
    (11 votes)
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  • leafers sapling style avatar for user Mido Yassoo
    I need to know more information about the difference between Peritubular Caps and Vasa Recta
    (6 votes)
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    • starky ultimate style avatar for user Sai
      The vasa recta is the meshwork capillary system that envelops the loop of henle - it's function is mainly for the maintenance of the concentration gradient.

      The peritublar capillaries are those capillaries around the PCT and DCT that function in reabsorbtance.
      (6 votes)
  • orange juice squid orange style avatar for user Anna Sherman
    But if you drink a lot of water, how does the kidney make the process go faster. If you drink a lot, you will have to go to the toilet sooner. why is that?
    (5 votes)
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    • leaf green style avatar for user Todd Fraser
      The big driver for urine output in this situation is not the volume of the fluid you drink, but the fact that it dilutes the electrolytes in your system. The body is very effective at keeping the concentration of electrolytes static. When you dilute them, your body senses this and inhibits the release of " anti-diuretic hormone". Without ADH, your kidneys filter off excess water, which increases your urine output.
      (10 votes)
  • female robot grace style avatar for user Anjali Mohapatra
    Do both the kidneys work at the same time or does the other works when the first one gets damaged??
    (2 votes)
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    • leaf green style avatar for user Joanne
      I see there are a couple of questions here and I will try to address both in this post. A person with 2 normal kidneys has both working at the same time producing urine. If one is damaged, then the other is working and we may not know one is damaged because blood urea nitrogen, BUN, remains normal. That person Doesn't' need a transplant unless the problem affects the second kidney as well. When damage progresses to the second kidney, and less than 2/3 is working well, then we will see an elevation of the BUN and creatinine in the blood. Urea building up, hydrogen ions increasing causing acidosis, high potassium ions, edema, etc. Indicate a transplant may be needed and dialysis is necessary because the person likely has chronic renal failure.
      (12 votes)
  • piceratops tree style avatar for user vixxyn
    at aren't the vasa recta a name for the specific peritubular capillaries surrounding the loop of henle, not a separate capillary bed?
    (5 votes)
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  • aqualine ultimate style avatar for user Parth Kumar
    How Are Kidney Stones Formed?
    (5 votes)
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    • male robot hal style avatar for user Roshan Maiya
      imagine your kidneys as filters in your body that clean your blood and remove waste products. Sometimes, certain substances in your urine (the liquid waste your body produces) can come together and form crystals. These crystals can stick together over time and create what we call kidney stones.
      (4 votes)
  • orange juice squid orange style avatar for user Cheryl Bautista
    at how does urine get to the bladder?
    (1 vote)
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    • piceratops ultimate style avatar for user Shriya
      Summary of urine production:
      1. Filtration: Blood enters the glomerulus through the afferent arteriole and filters into the surrounding capsule at the "head" of the nephron.
      2. Reabsorption: Useful substances are reabsorbed from the nephron tubule into the adjacent peritubular capillary.
      3. Secretion: waste products to be eliminated are taken up from the peritubular capillary into the nephron tubule.
      Urine formation = three basic processes: glomerulur filtration, tubular reabsorption, and tubular secretion/excretion, contribute to urine formation.
      The urine exits the kidney through the ureter and is transported to the bladder where it is excreted when the sphincter muscles are released.
      (11 votes)
  • leaf green style avatar for user Moriah Lawrence
    What happens to the waste if your kidneys don't work properly?
    (3 votes)
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  • blobby green style avatar for user jenmondok
    What does a low urine osmolarity and low glucose indicate?
    (2 votes)
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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.