What causes concentrated urine production in the kidneys of a desert-dwelling mammal, given limited water intake?

💡 Explanation

A concentrated urine results from a steep medullary osmotic gradient, created by the countercurrent multiplier system in the loop of Henle, because this allows for maximal water reabsorption via osmosis in the collecting duct. Therefore, a high osmotic gradient concentrates urine, rather than decreased permeability, reduced aldosterone, or elevated filtration pressure.

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