In-Depth Notes on the Cardiovascular System

Introduction to the Cardiovascular System

  • Overview of cardiovascular system, its anatomy and physiology.
  • Objectives:
    • Introduce cardiovascular system
    • Describe detailed anatomy of heart
    • Introduce contractile and autorhythmic cardiocytes
    • Explain conduction system and heart rhythm generation

Components of the Cardiovascular System

  • Three main parts:
    1. The Heart: Central pump propelling blood.
    2. Blood Vessels: Arteries, veins, capillaries for blood transport.
    3. Blood: Carries O2, nutrients, hormones (7-8% body weight).

Main Functions of Cardiovascular System

  • Transport Substances:
    • Oxygen and Nutrients: Metabolism support
    • Wastes: Transported to kidneys/liver for detoxification
    • Hormones/Immune Cells: Regulation and responses

Pathway of Blood Flow

  • Two Circuits:
    1. Pulmonary Circuit:
    • Right heart to lungs via pulmonary arteries, gas exchange (O2 in, CO2 out).
    • Blood returns to left heart via pulmonary veins.
    1. Systemic Circuit:
    • Left heart pumps to body tissues (excluding lungs) via arteries.
    • Wastes return through veins to right heart.

Anatomy of the Heart

  • Major Structures:
    • Atria: Upper chambers (receive blood)
    • Ventricles: Lower chambers (pump blood)
    • Valves: Facilitate unidirectional flow.

Detailed Anatomy

  • Pericardium: Encases heart; lubricates during beats.
  • Heart Wall Layers:
    1. Epicardium: Outermost, protective.
    2. Myocardium: Muscular layer, enables contraction.
    3. Endocardium: Smooth lining of chambers and valves.

Valves of the Heart

  • Function: Prevent backflow, maintain flow direction.
  • Types:
    1. Atrioventricular Valves:
    • Right AV (Tricuspid) Valve: Between right atrium/ventricle.
    • Left AV (Bicuspid/Mitral) Valve: Between left atrium/ventricle.
    1. Semilunar Valves:
    • Aortic Valve: Left ventricle to aorta.
    • Pulmonary Valve: Right ventricle to pulmonary artery.

Myocardial Cells

Types of Cardiocytes

  • Contractile Cells: 99%, responsible for the pumping action.
  • Autorhythmic Cells: Initiate heartbeats, include pacemaker cells in SA node.

Characteristics of Cardiac Muscle

  • Similar to skeletal muscle but with unique features:
    • Single nucleus, intercalated discs for cell communication, longer AP duration (250-300 msec) to avoid tetanus.

Conduction System of the Heart

  • Components:
    1. SA Node: Primary pacemaker, initiates electrical activity (70-80 beats/minute).
    2. AV Node: Delays conduction to allow filling of ventricles.
    3. Bundle of His and Purkinje Fibers: Convey impulses to allow coordinated contractions.

Electrical Activity

  • Initiated in SA Node, spreads through atria, delayed at AV Node to ensure proper filling, then distributed rapidly through bundle branches.

Action Potentials in Myocardial Cells

Autorhythmic Cells

  • Generate APs by ionic movements of Na+, K+, and Ca2+.
  • Firing Rates:
    • SA Node: 70–80 AP/min
    • AV Node: 40–60 AP/min
    • Bundle of His/Purkinje Fibers: 20–40 AP/min

Contractile Cells

  • Exhibit Five Phases AP:
    1. Phase 0: Rapid depolarization (Na+ influx).
    2. Phase 1: Brief repolarization (K+ efflux).
    3. Phase 2: Plateau (Ca2+ influx).
    4. Phase 3: Repolarization (K+ efflux).
    5. Phase 4: Resting potential established.

Cardiac Cycle Overview

  • Definition: Series of heart changes occurring with each heartbeat (systole versus diastole).

Main Phases

  1. Ventricular Filling: Atria contract, blood flows into ventricles through AV valves.
  2. Isovolumetric Contraction: Ventricles contract, pressure rises, AV valves close.
  3. Ventricular Ejection: Blood ejected from ventricles when systole occurs.
  4. Isovolumetric Relaxation: Ventricles relax; pressure decreases.

Measurement of Blood Pressure

  • Systolic Pressure: Peak during ventricular contraction.
  • Diastolic Pressure: Lowest during heart relaxation.
  • Pulse Pressure: Difference between systolic and diastolic pressure.
  • Mean Arterial Pressure: Average pressure during the cycle (MAP = 2/3 DBP + 1/3 SBP).

Cardiac Output and Regulation

  • Definition: Volume of blood pumped by each ventricle per minute (CO = HR x SV).
  • At rest, CO averages approximately 5 L/min.
  • Factors Influencing Stroke Volume:
    • Preload: Increased blood return enhances stretching/force of contraction (Frank-Starling mechanism).
    • Afterload: Arterial pressure impacts ejection of blood.

Arteriolar Resistance and Regulation

  • Intrinsic: Local metabolic signals control arteriolar constriction/relaxation adjusting blood to active tissues.
  • Extrinsic: Neural and hormonal signals modify blood flow to maintain system balance during activity.

Capillary Exchange

Mechanisms

  • Diffusion, Transcytosis, and Bulk Flow are key.
  • Starling Forces: Hydrostatic pressure pushes fluid out; osmotic pressure pulls fluid in.
  • Regulation Examples: Active/Reactive Hyperemia respond to metabolic needs.

Conclusion

  • Understand cardiovascular system dynamics, including heart functions, blood flow regulations, and exchange processes at capillaries, crucial for health maintenance.