Anatomy of the Heart

Anatomy of the Heart

  • The heart is a muscular double pump with two main functions:
    • Pulmonary Circuit: The right side receives oxygen-poor blood from the body and pumps it to the lungs.
    • Systemic Circuit: The left side receives oxygenated blood from the lungs and pumps it throughout the body.

Structure of the Heart

  • Atria: Receive blood from both the pulmonary and systemic circuits.
  • Ventricles: The pumping chambers of the heart.

Location and Orientation

  • The heart typically weighs between 250-350 grams.
  • It is the largest organ of the mediastinum, located between the lungs.
    • The apex lies to the left of the midline while the base is the broad posterior surface.

Coverings of the Heart

  • Pericardium: Two primary layers:
    • Fibrous Pericardium: Strong layer of dense connective tissue.
    • Serous Pericardium: Formed from two layers:
    • Parietal layer
    • Visceral layer (also known as the epicardium).

Layers of the Heart Wall

  • Epicardium: The outer layer, a visceral layer of the serous pericardium.
  • Myocardium: The middle layer consisting of cardiac muscle arranged in circular and spiral patterns for effective contraction.
  • Endocardium: The inner layer, endothelium resting on connective tissue that lines the heart's internal walls.

Heart Chambers

  • Atria: Right and left atria are the superior chambers.
  • Ventricles: Right and left ventricles are the inferior chambers.
    • Internal divisions include:
    • Interventricular septa
    • Interatrial septa
  • External markings include:
    • Coronary sulcus
    • Anterior interventricular sulcus
    • Posterior interventricular sulcus

Right Atrium

  • Forms the right border of the heart and receives oxygen-poor blood from:
    • Superior vena cava
    • Inferior vena cava
    • Coronary sinus
  • Contains pectinate muscles and features like the crista terminalis and fossa ovalis.

Right Ventricle

  • Receives blood from the right atrium through the right atrioventricular valve (tricuspid valve).
  • Pumps blood into the pulmonary circulation via the pulmonary trunk.
  • Internal structure includes trabeculae carneae and papillary muscles along with the pulmonary semilunar valve.

Left Atrium and Ventricle

  • Left Atrium: Forms the heart's posterior surface and receives oxygen-rich blood from the lungs through pulmonary veins. It opens into the left ventricle through the left atrioventricular (bicuspid) valve.
  • Left Ventricle: Forms the apex of the heart and has internal walls similar to the right ventricle. It pumps blood through the systemic circuit via the aortic semilunar valve.

Cardiac Skeleton

  • Surrounds all four valves and is composed of dense connective tissue, serving multiple functions:
    • Anchors valve cusps.
    • Prevents overstretching of valve openings.
    • Serves as a point of muscle insertion.
    • Blocks direct electrical impulse spread.

Heart Sounds

  • Produces the typical "Lub-dup" sounds:
    • First sound (Lub): Closure of the Atrioventricular (AV) valves.
    • Second sound (Dup): Closure of the semilunar valves.
  • Best heard near specific heart corners due to location:
    • Pulmonary valve: superior left corner.
    • Aortic valve: superior right corner.
    • Mitral valve: apex.
    • Tricuspid valve: inferior right corner.

Pathway of Blood Through the Heart

  • Blood flow sequence involves:
    • Entry of oxygen-poor blood via the superior and inferior vena cavae into the right atrium.
    • Passage through the tricuspid valve into the right ventricle, then through the pulmonary valves into the pulmonary trunk to the lungs.
    • Oxygen-rich blood returns to the left atrium via the pulmonary veins, moves through the mitral valve to the left ventricle, and then out through the aortic valve and aorta to the body.

Conducting System of the Heart

  • The heart generates and conducts electrical impulses, primarily starting from:
    • Sinoatrial (SA) Node: The main pacemaker.
    • Atrioventricular (AV) Node, then to the AV bundle, bundle branches, and Purkinje fibers.

Innervation and Control

  • Heart rate is influenced by both extrinsic and neural control via:
    • Parasympathetic Fibers: Part of the vagus nerve that decreases heart rate.
    • Sympathetic Nerves: Increase heart rate and contraction strength.
    • Regulated by the cardiac centers in the medulla.

Blood Supply to the Heart

  • Coronary Arteries: Supply blood to the muscular tissue of the heart:
    • Right Coronary Artery: Branches into marginal artery and posterior descending artery (
    • Left Coronary Artery: Branches into anterior interventricular (LAD) and circumflex arteries.

Cardiac Veins

  • Carry deoxygenated blood from the heart wall to the right atrium, with main veins including:
    • Coronary sinus
    • Great cardiac vein
    • Middle cardiac vein
    • Small cardiac vein

Disorders of the Heart

  • Coronary artery disease: Includes conditions like atherosclerosis.
    • Angina pectoris: Chest pain from reduced blood flow.
    • Myocardial infarction: Heart attacks due to blocked arteries.

Conduction System Disorders

  • Arrhythmias: Abnormal heart rhythms, including:
    • Ventricular Fibrillation: Rapid random impulses leading to cardiac arrest.
    • Atrial Fibrillation: Irregular impulses from atrial myocardium, increasing stroke risk.

Development of the Heart

  • Development begins by day 20-21, becoming functional around day 22. Key early structures:
    • Sinus venosus (will become parts of the right atrium)
    • Atrium
    • Ventricle (strongest chamber, develops into the left ventricle)
    • Bulbus cordis (contributes to pulmonary trunk and aorta).

Congenital Heart Defects and Changes with Age

  • Common defects include ventricular septal defect and result in inadequate oxygenation of blood.
  • Aging affects the heart through valve hardening, decline in cardiac reserve, and myocardium fibrosis. Regular exercise can mitigate some age-related decline.