Cardiac Development in Embryology

Cardiac Development

• Heart development starts at day 18 with endothelial cells dispersed at the cranial end of the mesoderm, forming the heart primordium.
• Endothelial cells form 2 endocardial tubes, initially closed by epithelium, which eventually dies to form a lumen.

Formation of the Cardiac Tube

• The 2 endocardial tubes fuse laterally, forming a single cardiac tube, which bends and folds to form the heart.
• The pericardial cavity forms above the cardiogenic area, and later becomes anterior due to craniocaudal folding.

Formation of the Heart Chambers

• The heart tube develops and bends, forming the atrium and sinus venosus dorsal to the truncus arteriosus, bulbus cordis, and ventricle.
• The sinus venosus develops 2 lateral expansions, called the right and left horns, and a body.

Septum Formation

• The interatrial septum forms, partitioning the common atrium into left and right atria.
• The septum primum forms, grows from the roof of the common atrium, and fuses with the septum intermedium, dividing the atrioventricular canal into right and left sides.
• The septum secondum arises, forming an oblique passage between the atria, and eventually closes the foramen ovale, leaving a depression called fossa ovalis.

Development of the Atria and Ventricles

• The sinus venosus develops 2 valves, right and left, which unite at the upper surface, forming the septum superium.
• The left horn atrophies, forming the coronary sinus and left atrium, while the right horn gets absorbed, forming the posterior smooth surface of the right atrium.
• Pulmonary veins are absorbed into the left atrium, making its smooth surface.

Development of the Truncus Arteriosus

• A spiral septum develops in the truncus arteriosus, dividing it into aorta and pulmonary trunk.
• The pulmonary artery joins the right ventricle, while the aorta joins the left ventricle.
• The pulmonary trunk moves right and anterior, then left and posterior to the aorta.

Formation of the Semilunar Valves

• Primordia of the semilunar valves become visible as 3 small tubercles, which hollow out at their upper surface, forming the semilunar valves "cusps".

Interventricular Septum Formation

• The muscular part of the interventricular septum forms from muscular outgrowth of the ventricles, while the membranous part forms from endocardial cushion.
• The spiral septum forms, dividing the truncus arteriosus into aorta and pulmonary trunk.

Congenital Anomalies

• Atrial Septal Defects (ASD): absence of septum primum and septum secundum, or excessive resorption of septum primum.
• Ventricular Septal Defect (VSD): absence of membranous part of IV septum.
• Fallot's Tetralogy: VSD, pulmonary stenosis, overriding of the aorta, and right ventricular hypertrophy.
• Transposition of Great Arteries (TGA): abnormal rotation or malformation of the aorticopulmonary septum, leading to right ventricle joining the aorta and left ventricle joining the pulmonary artery.
• Persistent Truncus Arteriosus: failure of development of the aorticopulmonary septum, often accompanied by VSD.

Learn about the formation of the heart in embryonic development, from the heart primordium to the formation of the endocardial tube and lumen.