Urea Treatment - A Kidney Question

[Wolverine2017]

Quick why question. From most sources, urea is reabsorbed from the tubule at around 40-60%. I am a little unclear on the biological significance of re-absorbing Urea since it is just a breakdown product - it seems to have no purpose once it is made - so why re-absorb it (this is taking energy right? whether secondary or primary active).

I am assuming it has to do with osmotic balance, but I just wanted to see if anyone else had a better answer.

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[kadler538]

You got it, it's a biological advantage to reabsorb urea. It draws water back into the interstitial space and helps create the gradient for water reabsorption via the Loop of Henle By the way, urea is not highly charged and so it doesn't have a difficult time passively diffusing down its gradient from the PCT into the blood. It's actively reabsorbed in the LOH.