Question

Mention the substances that exit from the tubules in order to maintain a concentration gradient in the medullary interstitium.

Answer 1

The concentration gradient in medullary interstitium is established primarily by renal tubules of the loop of Henle and the blood vessels surrounding them (vasa recta) in a process called countercurrent exchange.
The substances that exit from tubules for maintenance fo such gradient are mainly sodium chloride (NaCl), water and urea (contaning$H^{+},$ K and $N{H}_3^{+})$