Which embryonic structure forms the ventricular outflow tracts and the right ventricle?

• A. Truncus arteriosus
• B. Sinus venosus
• C. Endocardial cushion
• D. Bulbus cordis

Answer: (D)

The ventricular outflow tracts, especially the smooth outflow path of the right ventricle (the conus arteriosus), come from the bulbus cordis. This embryonic structure forms the outflow portion of the ventricles and, as development proceeds, contributes to the proximal parts of the great arteries after the aorticopulmonary septum splits the outflow tract into the aorta and pulmonary trunk. The right ventricle’s inflow is from the primitive ventricle, but its outflow tract specifically derives from the bulbus cordis. The other structures play different roles: the sinus venosus contributes to inflow at the venous end, the endocardial cushions help form the AV septa and valves, and the truncus arteriosus becomes the initial outflow trunk that is later divided into the aorta and pulmonary trunk.