The arterial baroreceptor reflex provides rapid short-term blood pressure regulation. In a patient who stands up suddenly (orthostatic challenge), the sequence of baroreceptor-mediated compensatory events is:

• A Reduced carotid sinus stretch → increased baroreceptor firing → parasympathetic activation to reduce cardiac output
• B Increased venous return to the right atrium activates Bezold-Jarisch reflex causing vasodilation
• C Carotid sinus pressure decrease → glossopharyngeal nerve stimulation → direct vasomotor center inhibition
• D Reduced carotid sinus stretch → decreased baroreceptor firing → sympathetic activation (tachycardia, vasoconstriction) + parasympathetic withdrawal ✓

Explanation

On standing, blood pools in the lower extremities, reducing venous return and cardiac output, which lowers arterial pressure. Reduced stretch of the carotid sinus and aortic arch baroreceptors decreases their afferent discharge. In the NTS (nucleus tractus solitarius), this reduces tonic inhibition of the RVLM (rostral ventrolateral medulla), increasing sympathetic outflow to the heart (positive chronotropy and inotropy) and blood vessels (vasoconstriction). Simultaneous withdrawal of parasympathetic tone further raises heart rate. These responses prevent syncope within 15-30 seconds of standing. Failure of this reflex causes orthostatic hypotension.

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

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