Lecture Notes on the Heart and Cardiovascular System

Introduction to the Heart

• The heart is a muscular organ responsible for pumping blood through blood vessels by repeated rhythmic contractions.
• Average human heart beats about 72 times per minute, but this number can vary slightly.
• Vital in circulating oxygenated blood to meet the cellular requirements of the body.
• Cardiac arrest, a condition where the heart stops, is a serious emergency.

Structure of the Heart

• The heart is a double pump with two circuits:
  • Systemic Circuit: Left side of the heart pumps oxygenated blood to the body.
  • Pulmonary Circuit: Right side of the heart pumps deoxygenated blood to the lungs.
• The heart is split into two halves:
  • Left side: Receives oxygenated blood from lungs and pumps it to the body.
  • Right side: Receives deoxygenated blood from the body and pumps it to the lungs.

Blood Flow and Heart Valves

• Blood vessels bringing deoxygenated blood to the right atrium:
  • Superior and inferior vena cava.
  • Coronary sinus.
• Movement of blood within the heart:
  • Right atrium → Tricuspid valve → Right ventricle → Pulmonary valve → Lungs.
  • Left atrium → Bicuspid/mitral valve → Left ventricle → Aortic valve → Body.
• Details on valves:
  • Atrioventricular valves (Tricuspid and Bicuspid/Mitral): Located between atria and ventricles.
  • Semilunar valves (Pulmonary and Aortic): Located at the exit points of ventricles.

Cardiac Conduction System

• A specialized system of cardiac muscle cells acting like nerves, controlling the heart rhythm.
• Main components:
  • Sinoatrial Node: Primary pacemaker, initiates contractions, located in the right atrium.
  • Atrioventricular Node: Secondary pacemaker, relays signals to ventricles.
  • Bundle of His: Pathway for electrical signals, directing them to the septum.
  • Purkinje Fibers: Coordinate contraction of ventricles.
• EKG/ECG is used to measure the heart's electrical activity and health.
• Indicators on an EKG:
  • P wave: Atrial depolarization.
  • QRS complex: Ventricular depolarization.
  • T wave: Ventricular repolarization.

Cardiac Cycle

• The cycle of events in a single heartbeat (0.8 seconds total).
• Phases of the Cardiac Cycle:
  • Late Ventricular Diastole: Heart is relaxed, passively fills with blood.
  • Atrial Systole: Atria contract, pushing blood into ventricles, ventricle pressure increases.
  • Early Ventricular Systole (Isovolumetric Contraction): Ventricles begin to contract, pressure rises but no blood ejected yet.
  • Late Ventricular Systole (Period of Ejection): Ventricles fully contract, semilunar valves open, blood is ejected.
  • Early Ventricular Diastole: Ventricles relax, semilunar valves close, brief period of isovolumetric relaxation.
• Heart Sounds: "Lub-dub" sounds due to valve closures.

Clinical Relevance

• EKG abnormalities can indicate conditions like atrial fibrillation or heart attack.
• Use of defibrillators in cases of cardiac arrest to restore normal heart rhythm.
• Personal anecdote on cardiac catheterization and angioplasty.

Summary

• The heart's structure and function are crucial for sustaining life.
• Understanding heart mechanics is key in diagnosing and treating cardiovascular diseases.