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Old 09-11-2011
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Default Most concentrated urine in absence of ADH

Which of the following sites will have most concentrated urine in the absence of ADH?

1) Proximal tubules
2) Descending loop of henle
3) Ascending loop of henle
4) Distal tubule
5) Collecting duct
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Old 09-11-2011
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is it 2) descending loop of henle ?

Its actually the part just distal to the descending loop of henle and proximal to the ascending loop of henle. If ADH is present then its the part distal to the collecting tubules.
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Old 09-11-2011
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4.distal tubules
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2) distal loop of Henle.
It is inpermeable to electrolytes, so the water is absorbed (and urea?)
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Quote:
Originally Posted by whocares13 View Post
Which of the following sites will have most concentrated urine in the absence of ADH?

1) Proximal tubules
2) Descending loop of henle
3) Ascending loop of henle
4) Distal tubule
5) Collecting duct
sure its 2 descending loop of henle and the tip of loop of henle has 1200mosm/l osmolarity greatest of all other tubules so the more osmolarity the more concenterated it is .. and as we know this segment has countercurrent multiplier system also ...
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Old 09-11-2011
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Yep, thin descending would be. Remember it is permeable to water, thus water will come out of the tubule, concentrating the solutes left in it to the same osmolarity as the interstitium (i.e. high).
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Correct Answer Answer

Yes, it is 2) Descending loop of henle

Explanation: ADH acts primarily on the collecting ducts, increasing their permeability to water. In the presence of ADH, the urine conc. will be highest at collecting duct but in the abscence of ADH, conc. will be highest at descending loop of henle. It is permeable to water and no reabsorbtion occurs in this segment, so the fluid in the lumen becomes hypertonic.
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