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Changing glomerular filtration rate

Get to know the renal system's glomerulus, the site of blood filtration. Learn how the diameter of arterioles influences the filtration rate and how substances like ions, amino acids, and glucose move through fenestrations into Bowman's space. Discover the impact of renal artery stenosis on filtration and the function of podocytes and tubule cells. Created by Raja Narayan.

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  • female robot ada style avatar for user Lauren
    How come people with infections have hematuria if there is a basement membrane preventing RBCs from entering the filtrate?
    (14 votes)
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    • leaf yellow style avatar for user adamzalaquett
      It can be caused by damage to the bladder or ureter itself causing blood to leak into the urinary tract. Things that may cause this are UTIs ans kidney stones. Also in hemolytic diseases, broken down blood cell particles may be able to pass through the basement membrane causing to urine to have red coloration.
      (37 votes)
  • aqualine ultimate style avatar for user Ben McCuskey
    I think I understand the effects on filtration with respect to the diameters of the afferent and efferent arterioles. However, I'm not sure if it was actually mentioned whether the efferent arteriole has a smaller diameter than the afferent arteriole. Does the afferent arteriole have a larger diameter than the efferent arteriole?
    (9 votes)
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    • leaf green style avatar for user Joanne
      Yes, the efferent arteriole has a smaller diameter, which makes sense because much of the plasma's volume was filtered into Bowman' s capsule so it doesn' t need to be as large as the afferent arteriole. However much of the water, electrolytes and nutrients are soon 're-absorbed in the proximal convoluted tubule. Since arterioles have smooth muscle they can also dialate and constrict to autoregulate GFR of the nephron.
      (7 votes)
  • duskpin ultimate style avatar for user haley
    In the endothelial cells there are holes where the waste leaves, correct? If this is true, I was just curious as to if there are diseases or sicknesses because of the holes being too big or too small and what they're called.
    (3 votes)
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    • piceratops ultimate style avatar for user Muffin
      Yes, there are "holes". The more correct way of saying that there are holes is that they are "fenestrated" (coming from the latin word "window"). A common misconception is that there are holes between the cells. Actually there are holes IN the cells.

      As far as I can tell, I've looked online and it doesn't seem like there are any diseases out there, but I could be wrong since I'm not a med student!

      I suspect that sizes won't make a huge difference because the basement membrane is semi permeable too, so is like a secondary filter, and should be a back up if the endothelial cells go wrong.
      (4 votes)
  • starky sapling style avatar for user XxTheBanexX
    Do you need both kidneys to live?
    (2 votes)
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  • marcimus pink style avatar for user browndonae80
    Why do people pee?
    (1 vote)
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  • aqualine sapling style avatar for user Tasneem Majid
    Is there a video where he talks about these kidney diseases mentioned at the very end?
    (2 votes)
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  • blobby green style avatar for user axel cardona
    how come people with infection have hematuria if there is a basement membrane preventing RBCs from entering the filtrate
    (2 votes)
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    • leaf green style avatar for user Joanne
      Blood in the urine is usually due to destruction of the epithelial lining of the bladder by bacteria, such as E. coli. If the E. coli travel up from the bladder to the kidneys, then it is possible they would damage the nephrons. A cystitis is a bladder infection and it is a more common problem, a nephritis is a nephron infection in the kidneys. In either case, bacteria damage the epithelium and the basement membranes that attach it to the connective tissue. When the epithelium of the bladder or the nephron is damaged, it bleeds just like when our skin is damaged. The blood goes into the bladder and we see hematuria.
      (2 votes)
  • blobby green style avatar for user Dew Drops
    May I ask where do the numbers in the Harris-Benedict equation for calculating BMR arise from?
    Also what about the number 140 in Cockcroft-Gault equation for calculating creatinine clearance?
    (2 votes)
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    • male robot hal style avatar for user Satwik Pasani
      I am not sure. If you look up the paper where they first propose the equation, you'll get your answer.

      In my opinion, it will mostly be an outcome of a multivariable regression. These numbers come form the observed data, what coefficients for the various variables best predict say the creatinine clearance. Although the factors that actually affect these numbers will be complicated, they are not "derived"as you would expect the coefficient of an equation to be.
      (2 votes)
  • duskpin tree style avatar for user Bernie
    Isn't there going to be the same amount of blood in the afferent, & efferent arteriole the whole time?
    (2 votes)
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    • leaf green style avatar for user Joanne
      No. Arterioles have smooth muscle so they dilate and constrict. As a result, the nephron can change the blood volume in the arteriole by constricting the blood vessel and that will change the pressure of the blood and thereby change the filtration rate. Perhaps re watch the video.
      (2 votes)
  • blobby green style avatar for user KEVIN
    I didn't understand what is the function of the podocyte cells? Can someone please explain?
    (2 votes)
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    • piceratops ultimate style avatar for user Joshua
      Podocytes are cells found in the Bowman's capsule located in the kidneys that wrap around capillaries of the glomerulus. Podocyte cells make up the epithelial lining of Bowman's capsule, the third layer through which filtration of blood takes place. The Bowman's capsule filters the blood, retaining large molecules (such as blood cell and proteins), whilst smaller molecules (such as water, ions, and glucose) are filtered as the first step in the formation of urine.
      (2 votes)

Video transcript

Voiceover: All right, so I think we have a pretty good appreciation of how we have some smaller ions, amino acids, glucose and even water than can leak through these fenestrations and get into this space right here. Remember, this is just Bowman's space. They can get into Bowman's space where we can then process them into the rest of the nephron. This is Bowman's space, and we have these podocytes that hug the arterioles right here by holding on to the endothelial cells. We also have this basement membrane that prevents giant proteins in our red and white blood cells from leaking through. And we have these tubule cells that help line the other side, and they're epithelial cells, they're in the class of epithelial cells. Excellent. Now the last thing I want to cover is what's happening here from having an arterial go into a structure and then give off another arterial. That's a little weird, right, because we usually like thinking about arterioles going into capillaries and then giving out a venule. Well one way to think about this is sort of like a marathon where there are a lot of people running on the same street from point A to point B, and they're either running in a narrow street or a wide street. Let's make a table to think about this. What would happen if we look at our afferent and our efferent arterioles, and we change the diameter of the vessel. What does that do to the rate of filtration? We'll write filtration right here. How does the diameter of our vessels change the rate of filtration? If we increase the diameter of the afferent arterial, or if we have a very wide path that allows a lot of marathon runners to run into the glomerulus, that means there's going to be a lot of blood here that includes all of the ions, and the amino acids and glucose, in addition to our blood cells and giant proteins we talked about. There's going to be a lot of stuff over here. So if there's a lot of stuff running over these fenestrations you're going to have a lot of leakage, and so there's going to be a lot of filtration. More filtration occurs if there are more people or more marathon runners running into this space right here, so more filtration. What about if we did that with the efferent arteriole? Let's say we increase the diameter of the efferent arteriole so there's space for more marathon runners to run away from this very narrow street, or this place where a lot of people can run off the pavement and get into these holes and go elsewhere. If we increase the diameter of our efferent arterial and allow people to leave, they're not going to be able to stay around here for a long period of time, they're not going to be near these fenestrations. That means that our filtration rate will decrease, because the blood is moving away from the place that it would be filtered. The same thing goes if we decrease the diameter of our afferent arteriole. If we decrease the amount of runners or blood that can come into the glomerulus, that means there's going to be less fluid filtered out, so a lower filtration rate. This is actually what happens with renal artery stenosis. If we have a very narrow or stenosed vessel - that's what stenosis means, it's just narrow - renal artery, that means there's going to be less blood that branches off and goes to our afferent arteriole. There's going to be less blood that runs across our fenestrations and is filtered away. On the flip side, if we decrease the diameter of our efferent arterial that makes it difficult for our runners to leave this fenestrated vessel, so there's going to be some backup, there's going to be a lot of ions and amino acids and glucose hanging around here near these holes. If blood backs up that means so do these guys, so then they're going to be filtered through these holes and collected into Bowman's space, so our filtration rate will increase, it will increase because there's a lot of backup that allows more time for filtration. Maybe if you're interested in learning about kidney diseases later on there's a lot of stuff that tweaks this system, that messes around with the afferent arterial or the efferent arterial, sort of like what I talked about for renal artery stenosis. I encourage you to think about what can go wrong with this process and how things can change, that's kind of the best way to learn about it. That's how our glomerulus works. Let's move on to the next part of our nephron.