Why does an elderly patient with impaired kidney function and reduced ADH secretion still experience a strong sense of thirst despite being mildly dehydrated?

💡 Explanation

The thirst mechanism is triggered by rising plasma osmolality. In elderly patients with kidney dysfunction, the osmolality set-point for triggering thirst can increase because of reduced renal concentrating ability and ADH response; therefore, even mild dehydration results in a strong thirst response at a higher osmolality, rather than other triggers dominating at lower osmolality levels.

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