Starting from the collecting duct, indicate the order in which urea molecules move to maintain the medullary concentration gradient.
(1) Ascending limb
(2) Distal convoluted tubule
(3) Interstitial fluid
(4) Collecting duct
(5) Descending limb
A) 2, 5, 1, 4, 3
B) 1, 3, 5, 2, 4
C) 3, 5, 1, 2, 4
D) 4, 2, 1, 3, 5
E) 4, 3, 5, 1, 2

Question

Quizplus · Accepted Answer

Urea moves from the collecting duct (4) into the interstitial fluid (3), then into the descending limb (5) of the loop of Henle. It does not typically move through the ascending limb (1) or the distal convoluted tubule (2) in significant amounts in this context, as these segments are relatively impermeable to urea. The correct sequence emphasizes the role of urea recycling in maintaining the medullary concentration gradient, crucial for the kidney's ability to concentrate urine.

Starting from the Collecting Duct, Indicate the Order in Which