A patient with long-standing essential hypertension has a mean arterial pressure of 130 mmHg. His carotid sinus baroreceptors continue to discharge rhythmically and buffer acute changes in pressure. The best explanation for this observation is:

• A Baroreceptors have been destroyed by the chronically high pressure
• B Baroreceptor input reaches the vasomotor center through the hypothalamus
• C Aortic baroreceptors alone mediate all buffering in chronic hypertension
• D Baroreceptors have reset their operating range upward over days to weeks ✓

Explanation

Baroreceptors adapt and reset within one to two days when arterial pressure stays elevated, shifting their firing curve so that maximal sensitivity lies near the new operating pressure. They therefore still buffer moment-to-moment fluctuations at 130 mmHg even though they no longer defend the old normal level. This resetting explains why the baroreflex cannot correct chronic hypertension, killing option A, since the receptors are functioning rather than destroyed.

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

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