Which ions enter the vasa recta?

$A$: The final reabsorption of water from urine into blood occurs through the collecting duct of a mammalian nephron,resulting in the production of hyperosmotic urine.
$R$: The loop of Henle is responsible for the formation of a sodium gradient across the depth of the medullary interstitium of a mammalian kidney.

Human urine as compared to human blood is

Explain the mechanism of formation of concentrated urine in mammals.

Human urine is usually . . . . . . compared to human blood.

Which part of the nephron plays a significant role in the maintenance of high osmolarity of the interstitial fluid?