Which of the following is the primary mechanism by which the baroreceptor reflex reduces blood pressure when arterial pressure rises acutely?

Question

Accepted Answer

B. Decreased sympathetic outflow and increased parasympathetic outflow to the heart. ## Baroreceptor Reflex Mechanism

**Key Point:** The baroreceptor reflex is the primary acute blood pressure regulation mechanism. When arterial pressure rises, baroreceptors in the carotid sinus and aortic arch increase their firing rate, triggering a parasympathetic response and withdrawal of sympathetic tone.

### Neural Pathway
1. Increased arterial pressure → baroreceptor stretch
2. Increased afferent signalling via CN IX (carotid sinus) and CN X (aortic arch)
3. Activation of nucleus tractus solitarius in the medulla
4. Increased parasympathetic (vagal) outflow → decreased heart rate and contractility
5. Decreased sympathetic outflow → vasodilation and reduced peripheral resistance
6. Net result: blood pressure falls

### Dual Response
| Component | Effect | Result |
|-----------|--------|--------|
| Parasympathetic ↑ | ↓ HR, ↓ contractility | ↓ Cardiac output |
| Sympathetic ↓ | Vasodilation | ↓ Peripheral resistance |
| Combined | Both reduce BP | Rapid pressure normalization |

**High-Yield:** The baroreceptor reflex operates within seconds and is the fastest blood pressure regulation mechanism. It is effective for acute fluctuations but not for chronic hypertension (baroreceptor adaptation occurs over days).

**Clinical Pearl:** Loss of baroreceptor function (as in carotid sinus hypersensitivity or after carotid surgery) results in orthostatic hypotension and blood pressure lability.

Answer

A. Direct inhibition of renin-angiotensin-aldosterone system activation

Answer

C. Increased sympathetic outflow to the heart and blood vessels

Answer

D. Decreased parasympathetic outflow and increased sympathetic tone

Which of the following is the primary mechanism by which the baroreceptor reflex reduces blood pressure when arterial pressure rises acutely?

Explanation

Baroreceptor Reflex Mechanism

Neural Pathway

Dual Response

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Component	Effect	Result
Parasympathetic ↑	↓ HR, ↓ contractility	↓ Cardiac output
Sympathetic ↓	Vasodilation	↓ Peripheral resistance
Combined	Both reduce BP	Rapid pressure normalization