Give a brief account of the counter current mechanism.

Production of concentrated urine is aided by the Henle’s loop and Vasarecta. The flow of filtrate in both the henle’s loop is in opposite direction and also in the vasa recta this flow is called as counter current pattern. The vasa recta is a capillary parallel to the henle’s loop. The Nacl which is transported by the ascending limb of the Henle’s loop is exchanged with the descending limb of vasa recta. In the same way small amounts of urea enter the thin segments of the ascending limb of Henle’s loop and again it is transported back to the interstitium. This exchange of materials facilitated by the Henle’s loop and vasa recta is called counter current mechanism.