Mechanism of urine concentration (Countercurrent mechanism of urine concentration).Both humans and animals form hypertonic urine. A countercurrent multiplier system is used for making urine a hypertonic. This procedure occurs in the Henle's loop and vasa recta. It involves mainly two ions i.e Sodium (Na+) and Chlorine (Cl-). Urine is isotonic in the proximal convoluted tubule. Henle's loop has a descending limb which is permeable to water. The tissue fluid surrounding it is hypertonic. Therefore, both the ions move in and the water moves out from the descending limb by passive transport. Finally, the filtrate becomes hypertonic in the descending limb.                                           (Image to be added soon)