Question

Urine is concentrated in loop of Henle in
A) Descending limb
B) Thick ascending limb
C) Hairpin bend between descending and ascending limbs
D) Area between ascending limb and distal convoluted tubule

Answer 1

Water current in the filtrate flows out of the duct through aquaporin channels in the papillary duct, passively flowing down its concentration gradient. This system reabsorbs water and produces concentrated urine to excrete.

Complete answer:
Henle's loop in the kidney is the section of a nephron that connects to the distal convoluted tubule from the proximal convoluted tubule. The Henle loop generates a region of high urea concentration far in the medulla; close the papillary duct throughout the collecting duct system, by way of a countercurrent multiplier system that utilizes electrolyte pumps.

Now, let us find the solution from the options-
- The thin descending limb, although strongly permeable to water, has poor permeability to urea and ions. In the renal medulla, the loop has a sharp bend moving from descending to ascending thin limb. Thus, option A is not the correct option.
-Water is impermeable to the thin ascending limb, but it is ion-permeable. Thus option B is not the correct option.
- In the two limbs of Henle’s ring, the movement of filtrate is in opposite directions and hence generates a counter current. The blood flow is also in a countercurrent direction via the two limbs of vasa recta. The proximity between Hairpin bend among Henle’s loop and vasa recta’s falling and ascending limbs, and also the countercurrent in them, tends to create condensed urine. Urine is also localized in the bend among descending and ascending limbs in the loop of Henle in Hairpin.
- A part of the kidney nephron among Henle’s loop and the collecting tubule is the distal convoluted tubule (DCT). It is partly responsible for sodium, potassium, calcium, and pH regulation. Thus, option D is not the correct option.

Thus, the correct answer is option (C) Hairpin bend between descending and ascending limbs.

Note: In a sequence of straight capillaries descending through cortical efferent arterioles, the loop of Henle is filled by blood. The vasa recta also has a multiplier countercurrent function that stops the medulla from washing solutes, thereby preserving the medullary concentration.