The Heart

THE HEART

AN INTRODUCTION TO THE HEART

  • Primary purpose: Pump to distribute blood throughout the body.

  • Heart beats about 100,000 times per day.

  • Pumps approximately 8000 liters of blood daily.

  • Blood flow: Heart -> Blood vessels -> Back to heart.

  • Pulmonary Circuit: Carries blood to and from the lungs.

  • Systemic Circuit: Carries blood to and from the rest of the body.

HEART CHAMBERS

  • Four chambers of the heart:

    • Right Atrium: Accepts blood from the body.

    • Right Ventricle: Pumps blood to the lungs.

    • Left Atrium: Accepts blood from the lungs.

    • Left Ventricle: Pumps blood to the body.

  • Atria contract together, followed by the ventricles.

  • Contractions result in a heartbeat, tightly controlled.

LOCATION OF THE HEART

  • Located near the anterior chest wall, behind the sternum.

  • Positioned in the mediastinum between the pleural cavities.

POSITION OF THE HEART

  • Base: Superior end where great vessels connect.

  • Apex: Inferior pointed tip.

  • Orientation:

    • Slight angle pointed left.

    • Anterior surface is more prominent than the right.

    • Most of the left ventricular wall is posterior.

PERICARDIUM

  • Surrounds the heart as a serous membrane consisting of two layers:

    • Visceral Layer (Epicardium): Lines the heart.

    • Parietal Layer: Lines the inner surface of the pericardial sac.

    • Serous Pericardium: Fluid-filled space reducing friction between layers.

HEART WALL STRUCTURE

  • Composed of three layers:

    • Epicardium: Covers outer surface of the heart (epithelium + areolar connective tissue).

    • Myocardium: Muscular wall of the heart (contains cardiac muscle, blood vessels, nerves).

    • Endocardium: Covers inside of chambers and heart valves (simple squamous epithelium + areolar connective tissue).

HEART WALL COMPONENTS

  • Myocardium levels:

    • Cardiac muscle enables twisting and squeezing action during contraction.

    • Composed of cardiomyocytes organized into bands spiraling around chambers.

CONNECTIVE TISSUE IN THE HEART

  • Abundant collagen and elastic fibers around cardiac muscle cells provide:

    • Support for cardiac muscle fibers, blood vessels, nerves.

    • Strength to prevent overexpansion of the heart.

    • Assists in returning the heart to its normal shape after contraction.

CARDIAC SKELETON

  • Tough, elastic connective tissue forming the fibrous skeleton:

    • Encircles bases of large vessels (pulmonary trunk and aorta).

    • Encircles each heart valve for stabilization.

    • Physically isolates atrial muscle from ventricular muscle for precise contraction timing and acts as an electrical insulator.

SURFACE ANATOMY OF THE HEART

  • Auricle: Expandable extension of an atrium visible on the surface.

  • Ligamentum Arteriosum: Fibrous band linking pulmonary trunk and aortic arch.

  • Coronary Sulcus: Groove marking the border between atria and ventricles.

  • Interventricular Sulci: Mark boundaries between left and right ventricles.

INTERIOR OF THE HEART

  • Septum: Muscular partitions (interatrial and interventricular) separating chambers.

  • Atrioventricular (AV) Valves: One-way valves allowing blood flow from atria to corresponding ventricles.

  • Semilunar Valves: One-way valves allowing blood flow from ventricles to exiting vessels.

ATRIOVENTRICULAR VALVES

  • Located between atria and ventricles preventing backflow:

    • Right AV Valve (Tricuspid): Three flaps or cusps.

    • Left AV Valve (Bicuspid or Mitral): Two flaps or cusps.

    • Function: Open and close responding to pressure changes during heart contractions.

SEMILUNAR VALVES

  • Prevent backflow into the ventricles:

    • Pulmonary Semilunar Valve: Prevents backflow from pulmonary trunk to right ventricle.

    • Aortic Semilunar Valve: Prevents backflow from ascending aorta to left ventricle.

HEART VALVE ACTION

  • When one set of valves opens, the opposite set closes to ensure unidirectional blood flow.

CARDIOPULMONARY CIRCULATION

  • Deoxygenated Blood Path:

    • Right atrium → Tricuspid valve → Right ventricle → Pulmonary trunk.

    • Pulmonary arteries → Lung capillaries (oxygen capture).

  • Oxygenated Blood Path:

    • Pulmonary veins → Left atrium → Bicuspid valve → Left ventricle → Aortic valve → Aorta.

CORONARY CIRCULATION

  • Supplies blood to cardiac muscle:

    • Arteries originate at the aortic sinuses.

    • Veins remove wastes and drain into coronary sinus.

  • Right Coronary Artery: Supplies right atrium and parts of both ventricles.

  • Left Coronary Artery: Supplies left atrium, left ventricle, and interventricular septum.

MYOCARDIAL INFARCTION (MI)

  • Commonly referred to as a heart attack:

    • Characterized by an area of dead tissue (infarct) due to compromised blood flow (ischemia).

  • Often results from coronary artery disease.

  • Treatment options include thrombolytic therapy, coronary angioplasty or bypass grafting.

HEARTBEAT

  • Coordinated contraction of atria and ventricles:

    • Includes contractile and conducting cells.

    • Action potential stages involve rapid depolarization, plateau, and repolarization in contractile cells.

CONDUCTING SYSTEM

  • Enables automaticity; cardiac muscles contract without neural input:

    • SA Node: Primary pacemaker, rates of 70-80 beats per minute.

    • AV Node: Secondary pacemaker if SA node fails (40-60 bpm).

ELECTROCARDIOGRAM (ECG or EKG)

  • Records electrical events of the heart, useful for diagnosing arrhythmias and cardiac activities.

THE CARDIAC CYCLE

  • Alternating periods of contraction (systole) and relaxation (diastole), involves:

    • Atrial systole

    • Atrial diastole

    • Ventricular systole

    • Ventricular diastole

HEART SOUNDS

  • S1: AV valves close.

  • S2: Semilunar valves close.

  • Other sounds may be associated with atrial contraction.

CARDIAC DYNAMICS

  • Stroke Volume (SV): Blood volume ejected by a ventricle.

  • Cardiac Output (CO): Blood volume ejected by left ventricle per minute (CO=SV x HR).

VOLUME REFLEXES

  • Heart adjusts HR and SV in response to blood volume changes:

    • Atrial Reflex: Adjusts heart rate based on increased blood return.

    • Frank-Starling Principle: Increased venous return leads to increased stroke volume.

AUTONOMIC INNERVATION

  • Dual innervation regulates heart rate:

    • Parasympathetic: Slows heart rate via vagus nerves.

    • Sympathetic: Increases heart rate and contractility.

HEART DEVELOPMENT

  • Involves formation from primitive tubes and structure to final position around 28 days of development.

DISORDERS OF THE HEART

  • Congestive Heart Failure (CHF): Heart cannot pump efficiently, causing fluid buildup.

TREATMENTS FOR FAILING HEARTS

  • Intra-aortic balloon pump (IABP)

  • Ventricular Assist Device (VAD)

  • Cardiomyoplasty (using skeletal muscle for support).