countercurrent multiplier system

A countercurrent multiplier system is a mechanism that expends energy to create a concentration gradient.

By means of a countercurrent multiplier system, which utilizes electrolyte pumps, the loop of Henle creates an area of high urine concentration deep in the medulla, near the collecting duct.

As the urine travels down the collecting duct system, it passes by the medullary interstitium which has a high sodium concentration as a result of the loop of Henle's countercurrent multiplier system.