In the nephron, the transport of substances like sodium chloride and urea is facilitated by a special arrangement called the counter-current mechanism, which comprises of:

$\text{NaCl}$ from the ascending limb of Henle's loop is exchanged with:

What is the range of osmolarity from the renal cortex to the inner medulla?

The concentration of urine depends upon $........$.

Medullary gradient is mainly developed due to

The increase in osmolarity from outer to inner medullary interstitium is maintained due to:
$(i)$ Close proximity between Henle's loop and vasa recta
$(ii)$ Counter current mechanism
$(iii)$ Selective secretion of $HCO_{3}^{-}$ and hydrogen ions in $PCT$
$(iv)$ Higher blood pressure in glomerular capillaries