If a hiker, experiencing severe dehydration, exhibits significantly elevated plasma osmolality, which mechanism restores fluid balance in the kidneys?

💡 Explanation

Elevated plasma osmolality triggers the release of antidiuretic hormone (ADH) from the posterior pituitary. ADH increases water reabsorption in the collecting ducts via insertion of aquaporins, a water channel, because this reduces the osmolality. Therefore, increased water reabsorption restores fluid balance, rather than increased filtration or altered sodium handling.

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