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Congenital Defects Tutorial
Normal Cardiac Development Fetal Circulation Congenital Heart Defects Cardiac Transplantation
Primary Heart Tube Systemic and Pulmonary Circulation Formation of Atrioventricular Valves Atrial Chambers Ventricular Septation Partitioning of Outflow Tract Conduction System Development of Blood Vessels Normal Anatomy and Relationships at Birth

Ventricular septation

  • Septation of the common ventricle involves contributions of septal structures that originate from both muscular and membranous tissues.
  • Between weeks 4 and 7, a midline protrusion referred to as the muscular interventricular septum grows upward between the expanding right and left ventricles.
  • Expansion ceases by 7 weeks prior to fusion with the atrioventricular septum, leaving an interventricular foramen that allows the left ventricle access to the ventricular outflow tract.
  • During the process of muscular interventricular septum expansion, the myocardium thickens begins to form infolding of tissue called trabeculations.
    • A prominent trabeculation called the moderator band forms on right wall of the muscular interventricular septum, connecting the septum with the anterior papillary muscle which attaches to the right atrioventricular valve.
  • The atrioventricular valves begin to form between weeks 5 and 7.
    • The leaflets of each valve arise from endocardial cushion tissues and form by a complex process not fully understood.
    • Remodeling of the ventricular myocardial walls frees the leaflets, leaving them connected to the walls via thin chordae tendinae and papillary muscles.
    • The left atioventricular valve has anterior and posterior leaflets and is referred to as the bicuspid or mitral valve while the right atrioventricular valve has three leaflets and thus is referred to as the tricuspid valve.
  • Complete septation of the right and left ventricles is normally completed by week 9 via fusion of the muscular interventricular septum with the conotruncal septum formed by fusion of conotruncal ridges (endocardial cushion tissue), and down-growth from the ventricular side of the atrioventricular septum.