bulbus cordis
Summary
The bulbus cordis is an embryonic structure derived from the primitive heart tube that gives rise to portions of the ventricles and outflow tract of the heart. It contributes to the smooth parts (outflow tracts) of the right and left ventricles and, along with the truncus arteriosus, forms the aorticopulmonary septum via neural crest cell migration.
Detail
During week 4 of embryogenesis, the primitive heart tube folds and forms distinct segments, one of which is the bulbus cordis, located distal to the primitive ventricle. The bulbus cordis gives rise to the conus arteriosus (outflow tract of the right ventricle, i.e., the smooth part of the right ventricle) and the aortic vestibule (smooth part of the left ventricle outflow). It works together with the truncus arteriosus (the most distal part of the heart tube) which forms the ascending aorta and pulmonary trunk. Neural crest cells migrate into the truncus arteriosus and bulbus cordis to form the aorticopulmonary septum, which spirals to separate the outflow tract into the aorta and pulmonary artery. Failure of neural crest migration or improper septation can lead to congenital heart defects such as transposition of the great vessels, persistent truncus arteriosus, and tetralogy of Fallot. Understanding the bulbus cordis is essential for grasping the embryologic basis of conotruncal congenital heart defects, which are heavily tested on USMLE Step 1. The primitive ventricle forms the trabeculated part of the left ventricle, while the primitive atrium forms the trabeculated parts of both atria, distinguishing the smooth versus trabeculated portions of the heart chambers based on embryologic origin.
Sources
- BRS Embryology
- First Aid for the USMLE Step 1
- Langman's Medical Embryology
- Moore's The Developing Human
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