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Old 02-05-2012
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Urine Sample Renal Clearance after Vasopressin Injection

A 45-year old female with polyuria receives a vasopressin injection. Her urinary output decreases significantly shortly afterwards. Renal clearance of which of the following substances would be most significantly reduced from baseline after the injection?

A) Glucose
B) Creatinine
C) Urea
D) Para-amino hippuric acid (PAH)
E) Calcium

Its a UW questions, it tripped me and couldn't understand even after reading the solution.
Answer with explanation.

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Old 02-05-2012
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Vasopressin = ADH

ADH acts on the collecting ducts by forming H2O porin channels and allows water to be reabsorbed.

I think the answer will be Urea ? I'm not sure lol
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Old 02-05-2012
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i also think its urea

glucose is always maximally reabsorbed so its reabsorption wont be affected
creatinine and PAH aren't reabsorbed so their clearance wont be affected
calcium... um maybe although i think its only affected in DCT by vit.D and PTH, not in CD by ADH and such.
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Old 02-05-2012
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Answer is Urea
I think the reason is urea is absorbed through the same porin channel under the influence of ADH.
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Old 02-05-2012
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Quote:
Originally Posted by jinni View Post
Answer is Urea
I think the reason is urea is absorbed through the same porin channel under the influence of ADH.
Thank you so much, i understood now. u r right
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Old 02-05-2012
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Ok let me try out here
Vasopressin increases water reabsorption in peritubular capillaries this result in hyposmolarity in the space outside tubules now as we move down the collecting duct urea is reabsorbed to maintain osmolarity increase hymo-osmolarity will increase urea absorption.
Glucose,Calcium,PAH and creatinin are not absorbed in collecting duct.
Hence they are not affected.
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Old 02-05-2012
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Similar concept here
Increased renal clearance in Alcohol Binge!
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Old 02-05-2012
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Quote:
Originally Posted by USMLEisnoteasy View Post
it was really helpful .thank you !
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