Why does severe dehydration cause rapid, potentially fatal, brain cell shrinkage in elderly patients, despite the plasma osmolality initially remaining within a near-normal range?

💡 Explanation

Elderly individuals often have a diminished thirst response and reduced ADH effectiveness; because of this, they cannot effectively respond to plasma osmolality changes during dehydration. The impaired thirst mechanism and ADH response then prevents adequate fluid intake and renal water reabsorption, therefore leading to brain cell shrinkage, rather than compensatory mechanisms maintaining cell volume.

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