Vasa recta is

Which one of the following animals has a longer loop of Henle?

The proximity between Henle's loop and vasa-recta as well as the counter-current in them help in maintaining an ...$A$... in molarity towards the inner medullary interstitium,i.e.,from ...$B$... $mOsmol \ L^{-1}$ in the cortex to about ...$C$... $mOsmol \ L^{-1}$ in the inner medulla. Here $A$,$B$,and $C$ refer to:

In human kidneys,which substances are mainly responsible for creating the osmolarity gradient of the medullary interstitial fluid?

Explain the mechanism of formation of concentrated urine in mammals.

In the given diagram,what are the regions $P, Q,$ and $R$?
$P \quad\quad Q \quad \quad R$