Which magnitude of change in its respective stimulus is required to produce a measurable increase in ADH secretion from the posterior pituitary?

• A A 5 percent rise in plasma osmolality
• B A 1 to 2 percent rise in plasma osmolality ✓
• C A 10 percent fall in arterial blood volume
• D A 25 percent fall in arterial blood volume

Explanation

The hypothalamic osmoreceptors are exquisitely sensitive: a rise in effective plasma osmolality of only 1 to 2 percent reliably increases ADH release, and thirst appears at around a 2 to 3 percent rise. Volumetric control through atrial and arterial baroreceptors is far less sensitive, generally requiring a fall of 10 to 15 percent in blood volume to drive ADH above what osmotic regulation alone would achieve. Option C describes the volume threshold, not the most sensitive stimulus, and options A and D exceed the true thresholds.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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