Blood Pressure Regulation

Key Components in Blood Pressure Regulation

• Heart: Cardiac output (heart rate × stroke volume).
• Blood Vessels: Peripheral resistance.
• Kidneys: Control of blood volume.
• Brain: Supervises and monitors all processes.

Major Factors Influencing Blood Pressure

1. Cardiac Output: Heart rate and stroke volume.
2. Peripheral Resistance: Affected by blood vessel diameter.
3. Blood Volume: Regulated by kidneys.

Blood Pressure Equation

• Mean Arterial Pressure (MAP) = Cardiac Output × Resistance
• MAP = Stroke Volume × Heart Rate × Resistance

Pressure Regulation

• Increased Stroke Volume/Heart Rate/Resistance: Increases MAP.
• Decreased Stroke Volume/Heart Rate/Resistance: Decreases MAP.

Regulation Mechanisms

Short-Term Regulation

• Neuronal Controls: Reflex arcs involving cardiovascular center, baroreceptors, and chemoreceptors.

  • Cardiovascular Center: Sympathetic neurons in the medulla, includes vasomotor center.
  • Baroreceptors: Respond to arterial pressure changes, inhibit cardioacceleratory centers when pressure is high, promote vasodilation.
  • Chemoreceptors: Respond to blood chemical composition; high CO2 levels trigger increased cardiac output and vasoconstriction.

• Hormonal Controls: Influence peripheral resistance and blood volume.

  • Adrenal Medulla Hormones: Epinephrine and norepinephrine increase cardiac output and vasoconstriction.
  • Angiotensin II: Stimulates vasoconstriction, affects renal function.
  • ADH (Antidiuretic Hormone): Increases blood volume.
  • Atrial Natriuretic Peptide: Decreases blood volume and pressure.

Long-Term Regulation

• Renal Regulation: Through direct and indirect mechanisms.
  • Direct Mechanism: Alters blood volume independently of hormones.
  • Indirect Mechanism: Involves renin-angiotensin-aldosterone system.
    • Low arterial pressure triggers renin release, converting angiotensinogen to angiotensin I, then to angiotensin II.
    • Angiotensin II actions: Increases aldosterone, ADH release, triggers thirst, acts as vasoconstrictor.

Hypertension

Definition and Effects

• Hypertension: Blood pressure ≥ 140/90 mmHg.
• Pre-Hypertension: Blood pressure between normal and hypertensive levels.
• Prolonged Hypertension: Risk for heart failure, vascular disease, renal failure, stroke.

Types

• Primary Hypertension: No specific cause, possible factors include genetics, diet, obesity, stress.
• Secondary Hypertension: Known causes such as renal artery obstruction, kidney disease, or endocrine disorders.

Management

• Lifestyle Changes: Diet modification, exercise, weight loss, smoking cessation.
• Therapeutics: Antihypertensive drugs, ACE inhibitors.

Hypotension

Definition and Types

• Hypotension: Blood pressure ≤ 90/60 mmHg.
• Orthostatic Hypotension: Temporary low BP when standing quickly.
• Chronic Hypotension: Often due to poor nutrition.
• Acute Hypotension: Sign of circulatory shock, inadequate blood circulation.

Types of Circulatory Shock

• Hypovolemic Shock: Due to large scale blood loss.
• Vascular Shock: Extreme vasodilation and decreased resistance.
• Cardiogenic Shock: Inefficient heart function.