Question

Give a brief account of the countercurrent mechanism.

Answer 1

Countercurrent mechanism is a mechanism that helps to create a concentration gradient to concentrate the urine to produce hyperosmotic urine.

Complete answer
-Production of hyperosmotic urine is necessary so that excess water is not released along with urine which can cause dehydration and other disorders.
-Vasa recta and Henle's loop plays an important role in the production of concentrated urine.
-The filtrate in the loop of Henle moves in the opposite direction in ascending and descending limbs which forms a counter-current.
-Similarly, the blood flows in the opposite direction in two limbs of the vasa recta which also forms a counter-current.
-This counter-current helps to increase the osmolarity of filtrate in the medulla, this osmolarity gradient is due to urea and NaCl.
-NaCl is transported through the ascending limb of Henle's loop and it is exchanged with the descending limb of the vasa recta and the NaCl returns to the inner medullary interstitium through the ascending limb of the vasa recta.
-The urea in the ascending limb of Henle's loop returns to the inner medullary interstitium through the collecting tubule.
-This entire mechanism is known as the countercurrent mechanism and this mechanism creates an osmolarity gradient that removes water from the collecting tubule to concentrate the urine.

Note: The Countercurrent mechanism was studied in the 1950s by scientists Gottschalk and Mylle, by referring postulates of Werner Kuhn and this experiment was demonstrated using the micropuncture experiment. Countercurrent mechanism helps to produce four times concentrated urine as compared to the initial filtrate.