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.