A patient presents with dehydration after prolonged vomiting. Which mechanism explains why the kidneys initially reduce urine output, but the urine becomes more concentrated with increased sodium?

💡 Explanation

Increased ADH secretion enhances water reabsorption in the collecting ducts due to the insertion of aquaporins, because this is the body's attempt to conserve water. Therefore, urine volume decreases and becomes concentrated with sodium, rather than sodium excretion being reduced or potassium increasing.

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