Answered

Which of the following is a correct statement regarding countercurrent exchange?

A. Flow of tubular fluid is bidirectional.
B. Water is not reabsorbed in the thick ascending limb because cells are impermeable to water.
C. The osmotic gradient where countercurrent exchange takes place is in the extracellular fluid of the medulla.
D. Principal cells in the collecting duct reabsorb more water when less ADH is present.



Answer :

Final answer:

Countercurrent exchange in the renal system involves the loop of Henle and vasa recta, facilitating concentration of urine.


Explanation:

Countercurrent exchange in the renal system takes place in the loop of Henle, where the descending limb is permeable to water and the ascending limb is impermeable to water but allows solutes to be reabsorbed. This setup creates a gradient that helps in concentrating urine. The vasa recta surrounding the loop acts as the countercurrent exchanger, aiding in maintaining the osmotic gradient.


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