Partitioning of outflow tract
- The outflow tract initially consists of bulbus cordis, truncus artirios, and the aortic sac with a common lumen which must be separated to connect future aorta to left ventricle and pulmonary artery to right ventricle.
- Conotruncal ridges (new cushion tissue)derived from neural crest cells and endocardial-derived cushion tissue grow inward along length of outflow tract in a spiral pattern in order to connect the definitive left ventricle to systemic circulation and definitive right ventricle to pulmonary circulation.
- Fusion of the conotruncal ridges begins in the distal truncus arteriosus then proceeds to the conus arteriosus forming the conotruncal septum that completely separates the right and left ventricular outflow tracts.
- When the formation of the outflow tracts is complete, conotruncal septum will have rotated a complete 180 degrees between the distal truncus arteriosus to the ventricles.
- This process of spiraling and complete septation is believed to be driven by forces generated in cardiac looping, myocardialization (replacement of cushion tissue with myocardial cells from outer myocardial wall), remodeling via apoptosis, and cardiac looping.
- The spiraling conotruncal ridges at the junction between the bulbus cordosis and truncus arteriosus act as primordia for the semilunar valves of both the aorta and pulmonary trunk.