What happens in the baroreceptor reflex when blood pressure rises?

• A. Increased baroreceptor firing reduces sympathetic tone and increases parasympathetic activity to lower heart rate and blood pressure.
• B. Baroreceptors trigger no change in autonomic tone.
• C. Increased baroreceptor firing increases sympathetic tone to raise blood pressure.
• D. Baroreceptors primarily influence respiratory rate and have little effect on heart rate.

Answer: (D)

The baroreceptor reflex rapidly regulates blood pressure by sensing stretch in the carotid sinus and aortic arch and adjusting autonomic output accordingly. When blood pressure rises, these baroreceptors fire more, signaling the brainstem to shift toward parasympathetic activity and away from sympathetic activity. This slows the heart rate and reduces contractility, while also dilating peripheral vessels as sympathetic tone decreases. The combined effect is a fall in cardiac output and systemic resistance, bringing blood pressure back toward normal. Respiratory rate is not the main target of this reflex, so the primary outcome is changes in heart rate and vascular tone to counter the rise in blood pressure.