Answer: Adding to medullary osmolarity, which aids water reabsorption from the duct.
- A Adding to medullary osmolarity, which aids water reabsorption from the duct
- B Reducing sodium reabsorption mainly along the nephron
- C Pumping water out of the collecting duct without any osmotic gradient
- D Diluting the medullary interstitium to limit water loss
Correct answer: A. Adding to medullary osmolarity, which aids water reabsorption from the duct
Explanation: Urea diffuses out of the collecting duct into the medullary interstitium and is recycled back into the loop of Henle, contributing to the high medullary osmolarity that drives water reabsorption from the collecting duct.
Filtrate flows through four functionally distinct stages of the nephron: Bowman's capsule filters blood, the PCT reabsorbs most useful substances unconditionally, the Loop of Henle builds a concentration gradient via counter-current exchange, the DCT secretes selected substances, and the collecting duct performs the final ADH-controlled water reabsorption.
Concept context
Nitrogenous waste, kidney structure, urine formation in the nephron, and hormonal regulation of excretion.
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