The Heart Anatomy and Function

Anatomy of the Heart

• Slightly larger than a clenched fist, the heart functions as a double, self-adjusting suction and pressure pump.
• Right heart receives poorly-oxygenated blood from the superior and inferior vena cavae, pumping it to the lungs through the pulmonary trunk for oxygenation.
• Left heart receives well-oxygenated blood from the lungs via pulmonary veins and pumps it into the aorta for systemic distribution.

Mediastinum & Position of the Heart

• Heart is located in the mediastinum, divided into superior and inferior parts, with the inferior mediastinum further segmented into anterior, middle, and posterior regions.
• The middle mediastinum contains the heart, pericardium, roots of great vessels, phrenic nerves, and pericardiacophrenic vessels.
• Heart is oriented obliquely, with 2/3 on the left and 1/3 on the right of the median plane, shaped like a three-sided pyramid.

Heart Structure

• Cardiac Apex: Formed by the left ventricle, located in the 5th intercostal space; movement known as the apical beat, palpable just left of the midclavicular line.
• Surfaces of the Heart:
  • Anterior (sternocostal) surface facing the ribs and sternum.
  • Diaphragmatic surface oriented toward the diaphragm, is formed by the left ventricle and right ventricle.
  • Posterior surface neighboring the esophagus.

Heart Borders

• Right Border: Formed by the right atrium, between superior and inferior vena cavae.
• Left Border: Formed mostly by the left ventricle and partially by the left auricle.
• Superior Border: Comprised of both atria and auricles, pulmonary trunk, aorta, and superior vena cava.
• Inferior Border: Mainly formed by the right ventricle.

Chambers of the Heart

• Comprises four chambers: left atrium (LA), right atrium (RA), left ventricle (LV), and right ventricle (RV).
• Interatrial septum divides the atria, while the interventricular septum divides the ventricles.

Right Atrium (RA)

• Receives venous blood from superior/inferior vena cavae and coronary sinus.
• Contains rough muscular wall (pectinate muscles), auricle, and a smooth-walled sinus venarum.
• Interatrial septum has a fossa ovalis, a remnant of the oval foramen.

Right Ventricle (RV)

• Largest part of the heart’s anterior surface and contains muscular ridges.
• Outflow tract leads to the pulmonary trunk via the pulmonary valve.
• Papillary muscles play a critical role in valve function.

Left Atrium (LA)

• Smaller than the right atrium, forming the base of the heart.
• Lined with pectinate muscles; four pulmonary veins terminate here.

Left Ventricle (LV)

• Forms the apex of the heart; has a muscular wall three times thicker than the right ventricle to handle systemic pressure.
• Contains a bicuspid (mitral) valve at the atrioventricular orifice leading to the aorta.

Interventricular Septum

• Composed of muscular and membranous parts, marked by external grooves indicating the separation between ventricles.

Cardiac Valves

• Atrioventricular Valves: Prevent blood reflux from ventricles to atria during contraction. Includes:
  • Tricuspid Valve: Right atrioventricular orifice with three cusps.
  • Bicuspid/Mitral Valve: Left atrioventricular orifice with two cusps.
• Semilunar Valves: Prevent regurgitation from the aorta and pulmonary trunk, located at arterial openings.

Conducting System of the Heart

• Coordinates heart contractions via specialized nodes and muscle bundles.
• Sinoatrial (SA) Node: Heart's pacemaker, located in the right atrium, generates impulses at 60-70 beats/min.
• Atrioventricular (AV) Node: Slower, starts impulses at 40-50 beats/min, located near the interatrial septum.
• AV Bundle (of His): Conducts impulses to ventricles, splitting into right and left bundle branches.

Heart Sounds and Auscultation

• Two heart sounds (lub-dub) correlate with the closure of valves; "lub" occurs during atrial contraction, while "dub" occurs during ventricular contraction.

Layers of the Heart Wall

• Epicardium: Outer layer, consists of the visceral layer of serous pericardium.
• Myocardium: Thick muscle layer responsible for contractions, comprising cardiac muscle, fibrous skeleton, and conducting structures.
• Endocardium: Inner layer of arteries/veins.

Skeleton of the Heart

• A layer of connective tissue separating atria from ventricles, it stabilizes and acts as an electrical insulator.

Overview of Papillary Muscles

• Three papillary muscles in the right ventricle attach to the tricuspid valve, preventing reflux during contraction.

The Heart

• Slightly larger than a clenched fist and functions as a double, self-adjusting suction and pressure pump
• Right heart receives poorly-oxygenated blood from the body and pumps it to the lungs via pulmonary trunk and arteries
• Left heart receives well-oxygenated blood from the lungs and pumps it into the aorta for body distribution

Mediastinum

• Located within the transverse thoracic plane, at the junction of T4 and T5 vertebrae
• Divided into superior and inferior parts, with the inferior mediastinum comprising anterior, middle, and posterior segments

Middle Mediastinum

• Contains the pericardium, heart, roots of great vessels, phrenic nerves, and pericardiacophrenic vessels
• The inferior wall of the pericardial sac attaches to the diaphragm's central tendon

Position and Orientation of the Heart

• Heart is obliquely positioned, with two-thirds to the left and one-third to the right of the median plane
• Shaped like a three-sided pyramid; apex points anteriorly and left, while the base points posteriorly
• Orientation varies with body type and respiration cycle

Cardiac Apex

• Formed by the inferolateral part of the left ventricle
• Located in the 5th intercostal space, with apical beat palpable along the left midclavicular line

Structure of the Heart

• Base directed superiorly, posteriorly, and to the right; apex directed inferiorly, anteriorly, and to the left
• Surfaces include:
  • Anterior (sternocostal) surface: adjacent to ribs and sternum
  • Inferior (diaphragmatic) surface: adjacent to the diaphragm
  • Posterior surface: adjacent to the esophagus

Borders of the Heart

• Right border formed by the right atrium, connecting superior and inferior vena cavae
• Left border primarily by the left ventricle and partly by the left auricle
• Superior border consists of both atria, pulmonary trunk, ascending aorta, and superior vena cava
• Inferior border mainly formed by the right ventricle

Cardiac Imaging

• A standard chest X-ray displays heart parts, great vessels, lungs, and domes of the diaphragm

Chambers of the Heart

• Comprises four chambers: left atrium, right atrium, left ventricle, and right ventricle
• Interatrial, interventricular, and atrioventricular septa separate the chambers

Right Atrium

• Receives venous blood from superior and inferior vena cavae and coronary sinus
• Contains a rough anterior wall with pectinate muscles and a smooth posterior wall
• Interatrial septum features an oval depression called fossa ovalis, a remnant of fetal circulation

Right Ventricle

• Largest part of the heart's anterior surface; divided into inflow and outflow tracts
• Inflow tract contains trabeculae carneae and is connected to the tricuspid valve by papillary muscles
• Outflow tract leads to the pulmonary trunk through the pulmonary valve

Left Atrium

• Smaller than the right atrium; forms most of the heart's base, with thin smooth walls
• Has four pulmonary veins draining into it; may possess a tissue fold known as valve of the oval foramen

Left Ventricle

• Forms the heart's apex with a thick muscular wall, performing more work than the right ventricle
• Contains a longer conical cavity with a mesh of trabeculae carneae
• Bicuspid/mitral valve governs left atrioventricular orifice leading to aortic vestibule

Interventricular Septum

• Composed of muscular (larger) and membranous parts
• External grooves mark its placement between cardiac chambers

Cardiac Valves

• Atrioventricular valves prevent reflux of blood between atria and ventricles
• Right atrioventricular (tricuspid) valve has three cusps; left atrioventricular (bicuspid/mitral) valve has two
• Semilunar valves at the pulmonary trunk and aorta have three crescent-shaped cusps that prevent regurgitation

Cardiac Sounds

• Heart sounds 'lub' (closure of atrioventricular valves) and 'dub' (closure of semilunar valves) are produced during contraction
• Blood flow direction affects sound propagation during auscultation

Heart Wall Structure

• Epicardium (outer layer), myocardium (middle layer composed of cardiac muscle), and endocardium (inner layer)

Skeleton of the Heart

• Connective tissue layer separating myocardium from atria and ventricles, providing mechanical stability and electrical insulation

Conducting System

• Includes SA node (pacemaker), AV node, and His bundle, which helps in coordinated contraction sequencing
• SA node located at the junction of superior vena cava and right atrium, generating impulses at 60-70 beats per minute
• AV node generates impulses at a slower rate of 40-50 beats per minute, not serving as the heart's primary pacemaker

Blood Supply to the Nodes

• Majority of blood to SA node from right coronary artery; some from left coronary artery