Why does severe dehydration lead to decreased glomerular filtration rate, reduced urine output, and increased plasma osmolality despite the body's compensatory mechanisms?

💡 Explanation

Dehydration reduces blood volume, causing lower renal perfusion. This triggers a lower glomerular filtration rate. The kidneys cannot adequately filter waste and reabsorb water in the collecting ducts because of reduced perfusion, therefore plasma osmolality increases, rather than decreasing, as ADH alone would imply.

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