Question

In mammals, which structure generates the NaCl gradient that allows the urine to be concentrated?

a. the collecting duct
b. the distal tubule
c. the loops of Henle
d. the proximal tubule

Answer 1

The loops of Henle, particularly the ascending loop of Henle, are responsible for generating the NaCl gradient essential for concentrating urine in mammals.

Step-by-step explanation:

In mammals, the structure that generates the NaCl gradient allowing the urine to be concentrated is the loops of Henle. Specifically, the ascending loop of Henle is responsible for actively pumping sodium chloride (NaCl) out of the filtrate, which leads to the hyperosmotic medullary interstitium essential for water reabsorption in the collecting ducts. This gradient is vital for allowing urine to be concentrated as it ascends through this part of the nephron. The complex interplay between the descending and ascending limbs of the loop of Henle, as well as the roles of the distal convoluted tubule and the collecting ducts, fine-tune the water and electrolyte balance and thus the final urine concentration.