Anatomy of the Heart

Introduction to the Cardiovascular System

The cardiovascular system is essential for transporting blood, nutrients, gases, and wastes throughout the body. It consists of the heart, blood vessels, and blood. Understanding the anatomy and physiology of the heart is foundational for comprehending how the cardiovascular system functions.

• Heart: Central pump of the cardiovascular system.

• Blood vessels: Arteries, veins, and capillaries that transport blood.

• Blood: Fluid medium carrying oxygen, nutrients, and waste products.

Cellular and Tissue Organization of the Heart

Cardiac Muscle Cell Morphology

Cardiac muscle cells, or cardiomyocytes, are specialized for continuous rhythmic contraction. They possess unique structural features that distinguish them from other muscle types.

• Small size and single, central nucleus

• Branching interconnections between cells

• Intercalated discs for electrical and mechanical coupling

• Two main cell populations:

  • Nodal (Pacemaker) cells: Initiate and regulate heartbeat

  • Contractile cells: Generate force for contraction

Tissues of the Heart

The heart wall is composed of three main layers, each with distinct tissue types and functions.

• Endocardium: Inner layer; simple squamous epithelium (endothelium) and areolar connective tissue

• Myocardium: Middle, muscular layer; cardiac muscle tissue, blood vessels, and nerves

• Epicardium (Visceral Pericardium): Outer layer; mesothelium and areolar connective tissue

• Parietal Pericardium: Lines the pericardial sac; mesothelium, areolar, and dense fibrous tissue

Pericardial Cavity and Pericardium

The heart is enclosed within the pericardial sac, which protects and anchors the heart while allowing movement during contraction.

• Fibrous pericardium: Outermost protective layer

• Parietal pericardium: Lines the inner surface of the pericardial sac

• Visceral pericardium (Epicardium): Covers the heart's surface

• Pericardial cavity: Space between parietal and visceral layers, containing pericardial fluid to reduce friction

Histology of the Heart Wall

Each layer of the heart wall has a specific structure and function:

• Epicardium: Produces serous fluid, protects the heart's exterior

• Myocardium: Thickest layer, responsible for contraction

• Endocardium: Smooth lining for chambers, continuous with blood vessel endothelium

Gross Anatomy of the Heart

External Features and Landmarks

The heart has four chambers and several external landmarks that are important for orientation and function.

• Right atrium: Receives blood from systemic circuit

• Right ventricle: Pumps blood to pulmonary circuit

• Left atrium: Receives blood from pulmonary circuit

• Left ventricle: Pumps blood to systemic circuit

• Coronary sulcus: Groove separating atria and ventricles

• Anterior and posterior interventricular sulci: Boundaries between ventricles

• Auricles: Flaps on atria

• Major vessels: Superior/inferior vena cava, aorta, pulmonary trunk, pulmonary arteries and veins

• Ligamentum arteriosum: Remnant of fetal ductus arteriosus

Internal Features and Landmarks

The internal anatomy of the heart includes septa, valves, and specialized muscle structures that ensure unidirectional blood flow and efficient contraction.

• Interatrial septum: Separates right and left atria

• Interventricular septum: Separates right and left ventricles

• Valves: Tricuspid (right AV), bicuspid/mitral (left AV), pulmonary, and aortic valves

• Chordae tendineae: Connect valve cusps to papillary muscles

• Trabeculae carneae: Muscular ridges in ventricles

• Moderator band: Conducts electrical signals in right ventricle

Right Atrium

The right atrium receives deoxygenated blood from the body and heart wall. It contains several important anatomical features:

• Openings: Superior vena cava, inferior vena cava, coronary sinus

• Foramen ovale (fetus): Connects atria during fetal development; becomes fossa ovalis after birth

• Pectinate muscles: Muscular ridges in anterior wall

• Auricle: Flap that increases atrial volume

Right Ventricle

The right ventricle pumps blood into the pulmonary circuit. Key features include:

• Trabeculae carneae: Muscular ridges

• Moderator band: Conducts electrical impulses

• Tricuspid valve: Three cusps, prevents backflow into atrium

• Chordae tendineae and papillary muscles: Prevent valve prolapse during contraction

Right Ventricle Outflow

The conus arteriosus leads to the pulmonary valve and trunk, directing blood to the lungs.

• Pulmonary valve: Prevents backflow into ventricle

• Pulmonary trunk: Splits into left and right pulmonary arteries

Left Atrium and Left Ventricle

The left atrium receives oxygenated blood from the lungs, while the left ventricle pumps it into the systemic circuit. The left ventricle has a thicker wall to generate higher pressure.

• Left atrium: Receives blood from pulmonary veins, contains auricle

• Bicuspid (mitral) valve: Two cusps, prevents backflow into atrium

• Left ventricle: Thicker myocardium, no moderator band, pumps blood through aortic valve into aorta

• Ligamentum arteriosum: Connects pulmonary trunk to aorta (fetal remnant)

Aortic Sinuses

Located at the base of the ascending aorta, these sacs prevent valve cusps from sticking to the aorta and are the origin of the coronary arteries.

Heart Valves and Cardiac Skeleton

Atrioventricular (AV) and Semilunar Valves

Valves ensure unidirectional blood flow through the heart and prevent backflow.

• AV valves: Between atria and ventricles; open during ventricular relaxation

• Semilunar valves: Pulmonary and aortic; open during ventricular contraction

• Chordae tendineae and papillary muscles: Prevent AV valve prolapse

• Valve disease: Inflammation (carditis) can lead to valvular heart disease (VHD)

Cardiac Skeleton

The cardiac skeleton is a framework of connective tissue that supports the heart's valves and electrically insulates the atria from the ventricles.

• Provides structural support and elasticity

• Stabilizes valves and prevents overexpansion

• Electrically insulates atrial and ventricular muscle fibers

Coronary Circulation

Coronary Arteries

The coronary arteries supply oxygenated blood to the heart muscle itself. They originate from the aortic sinuses.

• Right coronary artery: Supplies right atrium, portions of both ventricles, and conduction system

• Left coronary artery: Supplies left ventricle, left atrium, and interventricular septum

• Main branches: Circumflex artery, anterior interventricular artery, marginal arteries, posterior interventricular artery

Coronary Veins

Coronary veins collect deoxygenated blood from the myocardium and return it to the right atrium via the coronary sinus.

• Great cardiac vein: Runs in anterior interventricular sulcus

• Coronary sinus: Main venous drainage into right atrium

• Other veins: Posterior cardiac, middle cardiac, small cardiac, anterior cardiac veins

Summary Table: Heart Wall Layers

Review Checklist

• Cardiac muscle cell structure and function

• Heart wall layers and tissue types

• External and internal heart features

• Heart valves and cardiac skeleton

• Coronary circulation: arteries and veins