Role of Urea in the Kidney - Part 2
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- เผยแพร่เมื่อ 8 ก.ย. 2024
- There is a urea loop in the kidney, between the loop of henle and the collecting duct, that allows for a high concentration of urea in the medulla. This allows the body to excrete a high concentration of urea in the urine. For more videos and questions, visit - www.macrophage.co. Subscribe - goo.gl/EMRlRa. Support us on Patreon - goo.gl/bhmrgJ.
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Can i just say I have been searching for explanations on urea recycling for 2 days and yours is by far the best one, at least for me. Everything was so clear and your drawing were great.
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Nicely explained. Bonus point is that the explanation is simplified and very compact. 👍
Nice video (following on from Part 1). The only small point of disagreement at the end of Part 2 (from 2:28 onwards). The quote is that "[urea] is not as important for dragging water out of the urine in order to concentrate the urine ... How would you know that its not as important? ... when you allow a solute to go through a membrane, its no longer osmotically active. ..." While I agree that the comment about being osmotically active is quite true, I believe that the claim fails because it neglects the existence of the cycle (which leads to that high urea concentration), and neglects the fact that in the absence of the urea transporters urea will remain in the filtrate and act as an osmotic diuretic. So, here's a thought experiment - block the urea transporters in the collecting duct ... what happens to the water output? It goes up, because urea, by failing to be reabsorbed, would lead to a failure to reabsorb the water, and hence act as an osmotic diuretic.
Just a quick note: According to Costanzo's BRS Physiology, urea is actually secreted at thin descending limb, instead of thin ascending limb like you said.
The urea bieng cycled like that from thin ascending limb back to cd then again thin ascending limb he's talking abt the cycle
Actually it happens at both region i.e. across the whole thin segment, as discussed in chapter 36 in Walter Boron's physiology.
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Thank you
You made it easy. Thank you.
best explanation for urea recycling
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Thank you. Very clear explanation. I needed this!
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Thank you! Plain, simple, accurate.
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The last part is confused: Collecting duct urea transport KO mice are unable to concentrate urine to the same extent as wild type. If one places these animals on a low protein diet - less urea - then urinary concentrating ability is the same between KO and WT mice. This argues that urea enables mice to extract more water from the urine not that UTs are there in the IMCD to enable urea excretion.
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descending loop of henle is permeable to urea, NOT the ascending limb.
Why is a solute no longer osmotically active when it passes through a membrane?
I would say that it was a logical fallacy. A membrane has to be semipermeable (permeable to water but not all solutes) to allow for osmosis to occur. Furthermore, there needs to be an active transport of solutes over the membrane for a gradient to occur. If there were no channels there would be no osmosis because the fluids in the interstitium and lumen would be isotonic. Moreover, since the urea transporters in the collecting ducts are passive they will not contribute to water absorption there. They will however contribute to total water absorption because the circulation of urea will contribute to the osmolarity of the medulla.
Also the video doesn't take into account the effect of the vasa recta which also has urea transporters.
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I thought the urea transporters are in the descending rather than ascending limb of loop of Henley.
They're in both, but what he is talking about is urea recycling. The descending limb has urea transporters that allow urea to come in and out the nephron loop. Think of it like a revolving door. The nephron loves to hold onto urea, that's why it recycles it. It keeps the medulla salty, which draws out water, which the vasa recta will take. So in the loop of Henle it has channels that let out urea and let them in, like a night club where people are coming out and being allowed in according to the size of the club.. it's all about balance.
However he is talking about how the collecting duct has urea transporters that allow urea to COME OUT, making the medulla highly concentrated. The more concentrated the medulla, the better as it draws water out. Some of the urea then passively diffuses into the thin ascending limb through urea transporters, because like he said, half of the interstitial space is urea and Na+ and CL, so it wants to go where there is less of it. It then goes round and round. A mechanism which will always ensure that the medulla is highly osmotic.
This all makes sense. Nevertheless, if you have such a high concentration of these solutes plus urea deep in the medulla, why would water ever enter the vasa recta to be carried away into the bloodstream? Isn’t the blood in the vasa recta hypotonic with regard to the interstitial tissue deep in the medulla? It seems more logical that water would be sucked out of the vasa recta.
to prove that claim, u will have to do some calculations😁
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How do Na + and Cl- drive water out more efficiently than urea?
I would assume he means they do it more efficiently because they are actively transported.
Hello...
The force that drives water out of the tubules is the osmotic pressure and it has a formula...you can search for vant Hoff equation and see the formula.one of the factors in the formula is called sigma which ranges between 0 and 1. The sigma=1 means that the solute can not diffuse through the membrane . But if sigma=0 , it means that the solute freely diffuses the membrane. So if we have a solution with sigma=0, we won't have osmosis, because the solutes diffuse through the membrane and equilibrate , so the concentration of water will equilibrate in the two sides of membrane and there won't be any force for water movement. Sigma for urea is less than NaCl because it can move more easily through a membrane, because the membrane is mostly lipid and prefers the solutes that are free of charge(urea) rather than the ones with electrical charge(Na+ and Cl-)
@@zahratahmasbi4806 thank you for answering. I didn't know this concept 3 yrs ago. But now I'm finally in college. It was nice looking back at this question.
@@AS-ke6co you are welcome
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thank you!!