Question

Fluid within the loop of Henle is concentrated in the
A) Descending limb
B) Thick ascending duct
C) Hairpin bend between descending and ascending limbs
D) Bend between the ascending limb and the distal tubule

Answer 1

In the kidney, the section of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule is the loop of Henle. The key purpose of Henle’s loop is to establish a gradient concentration in the medulla of the kidney.

Complete answer:
First we should know about Henle’s loop to answer this question. Henle's loop is part of a nephron, a small tube that channels the solutes within the kidneys. The Loop of Henle is used in the nephron to build a concentration gradient that helps to improve the reabsorption of water and certain ions. Henle's loop is formed by two vasa recta, which are straight vessels that closely accompany the hairpin-shaped path of the tubule. The key feature of the Henle's loop is the recovery of sodium chloride and water from urine.
Now, let us find the solution-

Reabsorption in Henle’s loop is minimal. However, this area plays an essential role in preserving the elevated osmolarity of interstitial medullary fluid. The descending limb of Henle’s loop is water-permeable but almost electrolyte-impermeable. Which concentrates the filtrate as it passes down.
The ascending limb is impermeable to water, but consciously or unconsciously facilitates electrolyte transport. Therefore, it is diluted because of the transfer of electrolytes to the medullary fluid as the concentrated filtrate moves upwards.
From this we came to know that option A, B, and D are incorrect.

Thus, the correct answer is option ‘C’ Hairpin bends between descending and ascending limbs.

Note: In the two limbs of Henle’s loop, the movement of filtrate is in opposite directions and hence forms a counter current. The flow of blood is also in a countercurrent pattern via the two limbs of vasa recta. The similarity between the Hairpin bend between ascending and descending limbs of Henle’s loop and vasa recta, and also the countercurrent in them, tends to create concentrated urine. Urine is also localised in the bend between descending and ascending limbs in the loop of Henle in Hairpin.