Learning Objective

Understand how the hormonal feedback loop regulates blood pressure during hypotension and how it interacts with the autonomic nervous system.

Hormonal Feedback Loop (Endocrine Control of BP)

Trigger: Decrease in mean arterial pressure → ↓ renal perfusion

Kidney response: Juxtaglomerular cells release renin

Renin → Angiotensin system:

• Renin converts angiotensinogen → angiotensin I
• ACE converts angiotensin I → angiotensin II

Effects of Angiotensin II:

• Vasoconstriction → ↑ total peripheral resistance (TPR)
• Stimulates aldosterone release → ↑ Na⁺ and water retention → ↑ blood volume

Result: ↑ venous return → ↑ cardiac output → BP rises

Clinical Note

• Both autonomic (neural) and hormonal feedback loops are activated with antihypertensive therapy.
• Compensatory responses can cause:
  • Reflex tachycardia
  • Salt and water retention
• These effects can counteract BP-lowering drugs.

Activity