frostfly
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So in the loop of Henle, when sodium and chloride ions are pumped out of the ascending limb, do they diffuse into the vasa recta or into the ascending limb, or both, since there is a concentration gradient of these ions for both pathways?
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AortaStudyMore
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(Original post by Mystelle)
So in the loop of Henle, when sodium and chloride ions are pumped out of the ascending limb, do they diffuse into the vasa recta or into the ascending limb, or both, since there is a concentration gradient of these ions for both pathways?
So the ions diffuse into the vasa recta, the reason this works is because a counter current flow is established between the blood flow and the urine flow. So the osmolarity of the medullary interstitium is greater than in the cortical interstitium. As the blood in the vasa recta moves into the medulla, it picks up all the ions there and the blood omsolality increases, and then, as the blood leaves the medulla, it draws in all the water from the descending limb of the loop of Henle and so the blood leaves the kidneys with more water but is isotonic. This is always the case, and isn't naturally variable, if you want to vary the amount of fluid reabsorbed, then this is done in the collecting duct via aldosterone and vasopressin. Does this help?
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frostfly
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(Original post by AortaStudyMore)
So the ions diffuse into the vasa recta, the reason this works is because a counter current flow is established between the blood flow and the urine flow. So the osmolarity of the medullary interstitium is greater than in the cortical interstitium. As the blood in the vasa recta moves into the medulla, it picks up all the ions there and the blood omsolality increases, and then, as the blood leaves the medulla, it draws in all the water from the descending limb of the loop of Henle and so the blood leaves the kidneys with more water but is isotonic. This is always the case, and isn't naturally variable, if you want to vary the amount of fluid reabsorbed, then this is done in the collecting duct via aldosterone and vasopressin. Does this help?
Thank you, you’ve explained it perfectly - think you’ve even gone a bit beyond the A Level spec (we haven’t looked at aldosterone or vasopressin, just antidiuretic hormone)

One thing though, is counter current flow the same as counter current multiplier? I know counter current flow is also what you get in bony fish gas exchange surface. I’m slightly confused about whether a countercurrent flow/counter current multiplier is established between blood flow in vasa recta and loop of Henle, or between the ascending limb and descending limb of loop of Henle.
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AortaStudyMore
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(Original post by Mystelle)
Thank you, you’ve explained it perfectly - think you’ve even gone a bit beyond the A Level spec (we haven’t looked at aldosterone or vasopressin, just antidiuretic hormone)

One thing though, is counter current flow the same as counter current multiplier? I know counter current flow is also what you get in bony fish gas exchange surface. I’m slightly confused about whether a countercurrent flow/counter current multiplier is established between blood flow in vasa recta and loop of Henle, or between the ascending limb and descending limb of loop of Henle.
No worries, just a note though, vasopressin and ADH are the same.

Counter current multiplier is a type of counter current flow, and occurs in the loop of Henle, its purpose is to form a concentration gradient in the tubular intererstitium, which is the mechanism behind how we have varying concentrations of urine
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