Question

The function of counter current mechanism is performed by

1. Gills
2. Kidneys
3. Intestines
4. Lungs

Choose the correct option
A) 1 and 3 only
B) 2 and 4 only
C) 1, 2 and 4
D) 1, 2, 3 and 4

Answer 1

A countercurrent mechanism is a device that uses energy to generate a concentration gradient. It's abundant in nature, especially in mammalian organs. It may, for example, refer to the mechanism that underpins urine concentration, namely, the mammalian kidney's production of hyperosmotic urine.

Complete solution:
The function of counter current mechanism is performed by Gills, Kidneys, Intestines and Lungs
The nephrons of the human excretory system use the countercurrent multiplier, also known as the countercurrent mechanism, to concentrate urine in the kidneys.
Fish use a technique called countercurrent flow, in which blood and water flow in opposite directions through the gills to maximise oxygen diffusion. Fluid flows around the Henle loop in the kidney, where it exchanges with the interstitium and fluid streams travelling in opposite directions (descending and ascending) and because it causes osmolality to rise with depth in the medulla, the process is known as countercurrent multiplication. The blood vessels in the intestinal villi flow in a countercurrent pattern. Countercurrent flow in the alveoli aids in the diffusion of oxygen and carbon dioxide in the lungs.
Steps of countercurrent mechanism-
Henle Transport's Thick Ascending Loop
$\downarrow$
Equilibration of Henle's descending thin Loop
$\downarrow$
Flow of fluid
Countercurrent multiplication is often confused with countercurrent exchange, a related but distinct process that maintains but does not create gradients.

So the answer is option D

Note:
To avoid the washout of salts and preserve a high osmolarity at the inner medulla, the countercurrent multiplication mechanism works directly with the vasa recta's countercurrent exchange.