During hemorrhagic shock, the arterial baroreceptor reflex is activated. Which downstream effector response is the MOST immediate and physiologically prominent in restoring mean arterial pressure?
- A Activation of the renin-angiotensin-aldosterone system increasing plasma volume within minutes
- B Arteriolar vasoconstriction increasing total peripheral resistance ✓
- C Increased ADH secretion promoting water retention
- D Transcapillary refill from interstitial to intravascular compartment
Correct answer: B. Arteriolar vasoconstriction increasing total peripheral resistance
Explanation
The arterial baroreceptor reflex acts within seconds: decreased carotid sinus and aortic arch stretch triggers increased sympathetic outflow and reduced parasympathetic activity. The most immediate hemodynamic response is arteriolar vasoconstriction increasing TPR, which raises MAP directly (MAP = CO × TPR). RAAS activation (option A) takes 15-30 minutes; ADH (option C) acts over hours; transcapillary refill (option D) occurs over 15-30 minutes and is mediated by Starling forces, not the baroreceptor reflex per se.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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