29. Mention the substances that exit from the tubules in order to Maintain 3 concentration gradient in the medullary interstitium.
The concentration gradient in medullary interstitium is established primarily by renal tubules of 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 of such gradient are mainly sodium chloride (NaCl), water and urea (contaning H+, K+ and NH3+ ).
