Anatomy of Blood Pressure Regulation: The Science Behind BP Control in Your Body

1. What is Blood Pressure Regulation?

It is the mechanism by which the body maintains normal BP to ensure proper blood flow to organs.

Normal BP: 120/80 mmHg
Maintained by nervous system, hormones, kidneys, and local factors.

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TYPES OF BP REGULATION

A. Short-Term Regulation (Seconds to Minutes)

1. Baroreceptor Reflex

• Stretch receptors in:
• Carotid sinus (via glossopharyngeal nerve - CN IX)
• Aortic arch (via vagus nerve - CN X)
• Sense ↑ or ↓ in BP → send signals to vasomotor center (medulla)

Effects:

• ↑ BP → Baroreceptors activated → ↓ HR, vasodilation → ↓ BP
• ↓ BP → Less firing → ↑ HR, vasoconstriction → ↑ BP

2. Chemoreceptor Reflex

• Located in carotid body and aortic body
• Respond to ↓ O₂, ↑ CO₂, or ↓ pH
  → Activate sympathetic system → vasoconstriction → ↑ BP

3. Central Nervous System (CNS) Ischemic Response

• Occurs during very low cerebral blood flow
  → Strong sympathetic stimulation → ↑ BP

Mnemonic: "BBC Controls BP"

• Baroreceptors
• Brain (CNS) ischemia
• Chemoreceptors

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B. Long-Term Regulation (Hours to Days)

1. Renin-Angiotensin-Aldosterone System (RAAS)

1. ↓ BP → Kidney releases Renin
2. Renin converts angiotensinogen → Angiotensin I
3. ACE (in lungs) → converts it to Angiotensin II
4. Angiotensin II causes:
• Vasoconstriction → ↑ BP
• Stimulates Aldosterone → Na⁺ & water retention → ↑ BP

2. Antidiuretic Hormone (ADH or Vasopressin)

• Released from posterior pituitary when BP ↓ or osmolality ↑
• Causes water reabsorption in kidneys → ↑ blood volume → ↑ BP
• Also causes vasoconstriction

3. Atrial Natriuretic Peptide (ANP)

• Secreted by atria of heart in response to ↑ BP
• Causes:
• Vasodilation
• Excretion of Na⁺ & water → ↓ blood volume → ↓ BP

4. Kidneys (Direct Mechanism)

• Regulate blood volume
• Retain or excrete water & electrolytes to maintain BP

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C. Local/Autoregulation

• Organs adjust blood flow based on their needs
• ↓ O₂ or ↑ CO₂ → local vasodilation
• Important in brain, heart, kidneys

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SUMMARY TABLE

Type	Mechanism	Action on BP
Neural	Baroreceptors, Chemoreceptors	Fast ↑ or ↓ BP
Hormonal	RAAS, ADH, ANP	Long-term control
Renal	Water & Na⁺ balance	Maintains volume
Local	Autoregulation	Organ perfusion

Clinical Relevance

• Hypertension: Overactive RAAS or baroreceptor desensitization
• Hypotension: Blood loss, dehydration, shock
• Drugs:
• ACE inhibitors (↓ Angiotensin II)
• Beta-blockers (↓ sympathetic tone)