Learning Objective

Understand how the autonomic nervous system regulates blood pressure through baroreceptor-mediated feedback, and how pharmacologic agents can modify these reflexes.

Autonomic Feedback Loop (Neural Control of BP)

BP formula:

where CO = cardiac output, TPR = total peripheral resistance.

Detection:

• Baroreceptors in the carotid sinus and aortic arch detect changes in mean BP.
• Information is sent to cardiovascular centers in the brainstem.

Responses to ↑ BP:

• ↑ Baroreceptor firing → ↑ Parasympathetic (PANS) activity → bradycardia
• ↓ Sympathetic (SANS) activity → ↓ heart contractility and ↓ TPR
• Net effect: BP returns toward normal.

Responses to ↓ BP:

• ↓ Baroreceptor firing → ↓ PANS activity, ↑ SANS activity
• ↑ HR, ↑ contractility, ↑ TPR
• Net effect: BP increases toward normal.

Pharmacologic Modulation

Activity