The countercurrent mechanism is the mechanism that allows for the production of concentrated urine. The Henle's loop and vasa recta are the backbones of the mechanism.The flow of filtrate through the two limbs of Henle's loop and blood through the two limbs of the vasa recta are in a countercurrent pattern. This countercurrent flow contributes to an increase in osmolarity towards the inner medulla. The osmolarity gradient in the cortex ranges from 300mOsmol/L to 1200mOsmol/L in the inner medulla. The presence of such a gradient aids in the removal of water from the collecting duct, concentrating the urine.