plzzz answer fast morons..i have my exm tomorrow...!!!writ a note on counter current mechanism.

plzz fast

Concentration of urine is achieved by the presence of a concentration gradient in the medullary interstitium. Such concentration gradient is maintained by a specialised mechanism called the counter-current mechanism. 

For further information on the counter current mechanism, kindly refer to lesson 3; chapter 19 of our biology study material.