Cardiovascular System Notes

Position of Heart in the Thoracic Cavity

  • Heart located within the thoracic cavity; surrounded by structures ensuring its functionality.

The Pericardium

  • Definition: Double-walled sac surrounding the heart.
  • Functions:
    • Allows heart to beat without friction.
    • Provides room to expand while resisting excessive expansion.
  • Attachments: Anchored to the diaphragm (inferiorly) and sternum (anteriorly).
  • Structures:
    • Fibrous pericardium: Outer wall, not attached to the heart.
    • Serous pericardium:
    • Parietal layer: Lines fibrous pericardium.
    • Visceral layer (epicardium): Covers heart surface.
    • Pericardial cavity: Space between layers, filled with 5 to 30 mL of pericardial fluid.
    • Pericarditis: Painful inflammation of pericardial membranes.

Layers of the Heart

  • Epicardium:
    • External layer; visceral layer of serous pericardium.
    • Smooth, slippery texture.
  • Myocardium:
    • Contractile layer; 95% cardiac muscle.
  • Endocardium:
    • Inner layer; smooth lining for heart chambers and valves.

Chambers of the Heart

  • Atria:
    • Receiving chambers (right and left).
    • Auricles increase capacity.
  • Ventricles:
    • Pumping chambers (right and left).
  • Sulci: Grooves on heart's surface containing coronary blood vessels.
    • Coronary sulcus: Encircling the heart between atria and ventricles.
    • Anterior interventricular sulcus: Separates ventricles.

The Chambers Details

  • Interatrial septum: Wall separating atria.
  • Pectinate muscles: Internal ridges of myocardium in right atrium and auricles.
  • Interventricular septum: Muscle wall separating ventricles.
  • Trabeculae carneae: Internal ridges in ventricles.

Cardiac Muscle Tissue

  • Comparison with Skeletal Muscle:
    1. Smaller cells with larger & more numerous mitochondria.
    2. Striations present.
    3. Single (or double) centrally-located nucleus.
    4. Branching interconnections.
    5. Intercalated discs: Specialized connections (desmosomes and gap junctions).

Metabolism of Cardiac Muscle

  • Relies primarily on aerobic respiration for ATP.
  • Contains myoglobin and glycogen, with large mitochondria.
  • Uses fatty acids (60% of fuel), glucose (35%), and others (5%).
  • Resistant to fatigue and oxygen deficiency.

Autorhythmic Fibers

  • Specialized cardiac muscle fibers (1% of cells).
  • Self-excitable, generating action potentials triggering heart contractions.
  • Act as pacemakers and form conduction systems.

Myocardial Thickness

  • Different thicknesses:
    • Thin-walled atria: Deliver blood under low pressure.
    • Right ventricle: Pumps to lungs (short distance, lower pressure).
    • Left ventricle: Pumps to body (higher pressure, more resistance).

Heart Valves and Circulation

  • Atrioventricular valves: Tricuspid and bicuspid (mitral) valves.
  • Valve function during atrial and ventricular contraction.
  • Semilunar valves: Aortic and pulmonary valves; function during ventricular contraction.

Coronary Circulation

  • Myocardium has a dedicated network of blood vessels.
  • Coronary arteries branch from ascending aorta.
  • Important components:
    • Right coronary artery (supplies right atrium, some ventricles).
    • Left coronary artery (supplies left atrium, left ventricle).

Angina and Heart Attack

  • Angina pectoris: Chest pain from partial coronary obstruction.
  • Myocardial infarction (MI): Sudden death of myocardium due to long-term coronary obstruction.

The Conduction System

  • Begins at the sinoatrial (SA) node in the right atrium, propagates through the heart.

Pacemaker Physiology

  • PACEMAKER potential: Gradual depolarization due to Na+ inflow; triggers heartbeats.

Action Potentials and Contraction

  • Stages of ventricular myocardium action potential:
    • Depolarization (Na+ influx).
    • Plateau phase (Ca2+ influx).
    • Repolarization (K+ efflux).

Electrocardiogram (ECG)

  • Record of the electrical activity of the heart; contains P, QRS, and T waves.

Cardiac Cycle

  • Sequence of events during one heartbeat:
    • Phases:
    1. Ventricular filling
    2. Isovolumetric contraction
    3. Ventricular ejection
    4. Isovolumetric relaxation
  • Heart sounds are primarily due to closure of heart valves (Lubb-Dupp).

Regulation of Stroke Volume

  • Influenced by preload, contractility, and afterload.
  • Frank-Starling law: More blood in = greater contraction force.

Lymphatic System Overview

  • Functions to maintain fluid balance, immunity, and lipid absorption.
  • Lymph: Recovered fluid; Lymphatic vessels: transport lymph.

Lymphatic Tissues and Organs

  • Lymph nodes: Act as filters; contain lymphocytes for immune response.
  • Thymus: Important for T cell development; size diminishes with age.
  • Spleen: Filters blood, detects pathogens, and regulates the blood volume.