What is counter current mechanism explain about in long ,their functions and uses?

Countercurrent Mechanism: Concentrated Urine Formation----Unless one is drinking very large quantities of water, the urine has to be excreted in a concentrated form. Otherwise, the body will lose a lot of water and the person will suffer from the effects of dehydration and low blood pressure. The mechanism that the kidneys use to concentrate urine is called the countercurrent mechanism. In order to understand countercurrent mechanism, first, we have to understand how a countercurrent multiplier works.