Blood pressure regulation

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Blood Pressure Regulation

BP is regulated through two main timeframes: Short-term (neural via baroreceptors) and Long-term (renal via hormones).

1. Short-Term: Baroreceptor Reflex

Located in the Carotid Sinus (CN IX) and Aortic Arch (CN X). Responds to stretch.

Change in BP Firing Rate Reflex Response
Increase Increase Parasympathetic tone ↑, Sympathetic tone ↓.
Decrease Decrease Sympathetic tone ↑, Vasoconstriction ↑.

2. Long-Term: RAAS System

  • Renin: Released by JGA in response to low renal perfusion, low NaCl, or sympathetic activity.
  • Angiotensin II: Potent vasoconstrictor; increases sympathetic activity and stimulates aldosterone release.
  • Aldosterone: Increases Na^+ reabsorption and K^+/H^+ excretion in the distal tubule.

Physiology Board Hint: For test questions, remember that the carotid sinus is the primary sensor for BP fluctuations, but only the carotid responds to *both* decreases and increases. The aortic arch mainly responds to *increases* in BP. If you see a patient on an ACE inhibitor, remember: they have decreased Angiotensin II, leading to lower peripheral resistance and lower aldosterone.