Cardiovascular System Notes

Cardiovascular System Overview

  • Four Main Functions:
    1. Supply active muscles with oxygen and nutrients.
    2. Remove metabolic byproducts.
    3. Regulate blood pressure.
    4. Contribute to thermal regulation.

Cardiovascular Components

  • Four Main Components:

    1. Pump: The heart circulates blood.
    2. Distribution Circuit: High-pressure arteries.
    3. Exchange Vessels: Capillaries allow nutrient exchange.
    4. Collection Circuit: Low-pressure veins return blood to the heart.

  • Extent of Blood Vessels:

    • Approx. 60,900 km (100,000 miles) of blood vessels in an average-sized adult.
    • Total blood volume in the systemic and pulmonary circuits varies.

Blood Flow Dynamics

  • Blood Volume by Organ/Area:
    • Heart: 360 mL (7% of total)
    • Lungs: 130 mL (2.6% of total)
    • Arteries: 300 mL
    • Veins: 2300 mL (46% of total)

The Heart

  • Structure and Function:

    • Four chambers (right/left atria & ventricles).
    • Pumps about 70 mL of blood per beat.
    • Interconnected cardiac cells enable coordinated contraction via intercalated discs.

  • Cardiac Cycle Phases:

    • Systole: Ventricles contract, ejecting blood (systolic BP measures peak pressure).
    • Diastole: Heart relaxes, allowing chambers to refill with blood (diastolic BP measures residual pressure).

Blood Pressure Measurement

  • Systolic Blood Pressure (SBP): Peaks during ventricular contraction (avg. 120 mm Hg at rest).
  • Diastolic Blood Pressure (DBP): Lowest pressure during heart relaxation (avg. 60-80 mm Hg).
  • Mean Arterial Pressure (MAP): Average pressure during a cardiac cycle, calc. as
    MAP = DBP + [0.333 imes (SBP - DBP)]

Factors Affecting Blood Pressure

  • Blood Pressure Equation:
    BP = Cardiac Output imes Total Peripheral Resistance
  • Total Blood Volume & Resistance: Changes during physical activity increase blood flow, and vasodilation ensures sufficient supply to active tissues.

Muscle and Heart Interaction

  • Muscle Contraction and Blood Flow:
    • Exercise increases blood flow to active muscles; vasodilation occurs with increased local metabolites from activity.
    • "Muscle pump" aids venous return to the heart.

Myocardial Blood Flow

  • Rest & Activity:
    • At rest, approx. 70-80% of oxygen in coronary blood is extracted by the myocardium.
    • Blood flow increases with activity to meet the oxygen demand (increases by 4-fold during vigorous activity).

Rate-Pressure Product (RPP) Overview

  • RPP Relation: Reflects myocardial oxygen demand, calculated as
    RPP = SBP imes HR
  • Typical ranges from 6000 at rest to above 40,000 during significant exertion.

Hypertension

  • Definition: Chronic elevation of blood pressure, with possible readings exceeding 130/80 mm Hg.
  • Prevalence: Increasing with age and lifestyle factors.
  • Consequences: Risk of stroke, heart disease, and kidney failure.

Treatment Strategies for Hypertension

  • Lifestyle Changes:
    1. Regular physical activity.
    2. Healthy diet (DASH).
    3. Stress management.
    4. Medication when lifestyle changes are ineffective.