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Can someone please explain me the chart that's in FA relating to Acute Renal Faillure.

For example I understand that there's 3 types or causes or renal failure.

PRERENAL: Is due to a decrease in renal blood flow to the kidneys due to for example blood loss, CHF, Hypotension. Here the kidney is going to have a decrease RBF and therefore a decrease in GFR. So in order to compensate it retains sodium, water, and urea.
The table says that osmolarity in urine is increased, which I don't understand why since you are reabsorbing sodium and the sodium is the one that's correlated with osmolarity. Right?????? And why is the urine osmolarity greater than 500 if the sodium in urine is less than 10.:confused::confused::confused:

And what is Fe(NA)??????

RENAL: I understand that's due to damage to the kidney of course so you can't filtrate and you have decrease GFR. You cannot reabsorbe urea or electrolites. So why is the osmolarity decreased and the urine sodium grater than 20.

Same thing with posterenal causes, like obstruction due to BPH, Renal stones, tumor, and others. Why here is sodium greater than 40 and osmolarity less than 350.

Really need some help here.
If I don't clear this concept I can't go forward with the studying, just a weird OCD.:)):)):)):)):))
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