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Why urine osmolarity is low in oliguric phase of ac tubular necrosis although high urine Na
Why hypokelemia occurs in diuretic phase of ATN

Originally Posted by busy08

Why urine osmolarity is low in oliguric phase of ac tubular necrosis although high urine Na

ATN is intra-renal failure. Therefore, your fractional sodium in the urine is >2% because your PCTs aren't reabsorbing it. This means water is not reabsorbed as readily as well (because it would normally follow Na+ and Na+ isn't being reabsorbed), meaning that osmolarity of the urine must be low (i.e. <350 mOsm).

Originally Posted by busy08

Why hypokelemia occurs in diuretic phase of ATN

As the PCT epithelium is being replaced during the polyuric phase, PCT sodium reabsorption still cannot occur. The cortical principal cells, under the influence of aldosterone, will attempt to reclaim some of the Na+ not reabsorbed at the PCT. This will lead to kaliuresis due to the basolateral ATPase pump upregulation. Whereas Na+, K+ and H+ are all elevated in the serum during the oliguric phase, potassium and protons are reduced/normal during the polyuric phase.

Originally Posted by Phloston

ATN is intra-renal failure. Therefore, your fractional sodium in the urine is >2% because your PCTs aren't reabsorbing it. This means water is not reabsorbed as readily as well (because it would normally follow Na+ and Na+ isn't being reabsorbed), meaning that osmolarity of the urine must be low (i.e. <350 mOsm).




As the PCT epithelium is being replaced during the polyuric phase, PCT sodium reabsorption still cannot occur. The cortical principal cells, under the influence of aldosterone, will attempt to reclaim some of the Na+ not reabsorbed at the PCT. This will lead to kaliuresis due to the basolateral ATPase pump upregulation. Whereas Na+, K+ and H+ are all elevated in the serum during the oliguric phase, potassium and protons are reduced/normal during the polyuric phase.

Thanks for replying. there is hyponatremia in oliguric phase according to UW QID 886

Originally Posted by busy08

Thanks for replying. there is hyponatremia in oliguric phase according to UW QID 886

I have from Kaplan QBank: "Renal failure causes increased serum levels of all ions normally excreted (H+, K+, Na+)."

If anything, because GFR is decreased in oliguria, there could be a dilutional hyponatraemia, but serum Na+ should be increased.