Decoding Blood Pressure: Anatomy and Regulation of BP Explained

1. What is Blood Pressure?

• Blood pressure (BP) is the lateral force exerted by circulating blood on the walls of blood vessels, especially arteries.
• It is highest in arteries, lower in veins.

Normal BP:
Systolic = ~120 mmHg
Diastolic = ~80 mmHg
→ So, normal BP = 120/80 mmHg

---

2. Components of BP

Component	Description
Systolic BP	Pressure during ventricular contraction
Diastolic BP	Pressure during ventricular relaxation
Pulse Pressure	Systolic - Diastolic (normally ~40 mmHg)
MAP (Mean Arterial Pressure)	Diastolic + 1/3 × Pulse Pressure

3. Sites to Measure BP

• Common: Brachial artery
• Others: Radial, popliteal, femoral, dorsalis pedis arteries

---

4. Factors Influencing BP

Factor	Effect on BP
Age	↑ with age
Emotions/Stress	↑ BP
Exercise	Temporary ↑
Sleep	↓ BP
Obesity	↑ BP
Posture	Standing ↓ BP

REGULATION OF BLOOD PRESSURE

---

1. Short-Term Regulation (Seconds to Minutes)

A. Neural Mechanisms

• Controlled by Vasomotor center in the medulla oblongata
• Baroreceptors:
• Location: Carotid sinus & aortic arch
• Detect stretch (BP change) → send signals to brain
• Chemoreceptors:
• Detect changes in O₂, CO₂, pH

Response:

• ↑ BP → Baroreceptor firing → Parasympathetic activation → ↓ HR & BP
• ↓ BP → ↓ Baroreceptor firing → Sympathetic activation → ↑ HR, vasoconstriction → ↑ BP

---

2. Long-Term Regulation (Hours to Days)

A. Renin-Angiotensin-Aldosterone System (RAAS)

1. ↓ BP → Kidneys release Renin
2. Renin → converts angiotensinogen → Angiotensin I
3. ACE converts it to → Angiotensin II
4. Effects:
• Vasoconstriction → ↑ BP
• Stimulates Aldosterone → ↑ Na⁺ & water retention → ↑ blood volume → ↑ BP

B. ADH (Vasopressin)

• Secreted by posterior pituitary
• Promotes water reabsorption in kidneys → ↑ blood volume → ↑ BP

C. Atrial Natriuretic Peptide (ANP)

• Released by right atrium when BP ↑
• Causes vasodilation & excretion of Na⁺ → ↓ blood volume → ↓ BP

---

3. Autoregulation (Local Control)

• Tissues regulate their own blood flow by:
• Vasodilation when O₂ ↓ or CO₂ ↑
• Vasoconstriction when O₂ is adequate

---

Mnemonic for Hormonal BP Control: “RAA-A”

• Renin
• Angiotensin II
• Aldosterone
• ADH

---

4. Clinical Terms

Term	Meaning
Hypertension	BP > 140/90 mmHg
Hypotension	BP < 90/60 mmHg
Shock	Critically low BP → inadequate perfusion
Orthostatic hypotension	Sudden ↓ BP on standing