Heart tube looping, cardiac septation steps, and the specific congenital heart defect tied to each disrupted step tested on USMLE Step 1.
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- From what type of mesoderm does the primitive heart tube develop?
- Splanchnic (lateral plate) mesoderm
- Around what day of gestation does the primitive heart begin to beat?
- Day 22
- In normal development, which direction does the primitive heart tube loop?
- To the right (rightward, D-looping)
- What congenital defect results when the heart tube loops to the left instead of the right?
- Dextrocardia
- Listed from the venous to the arterial end, the primitive heart tube's five segments are the sinus venosus, primitive atrium, primitive ventricle, bulbus cordis, and ____.
- truncus arteriosus
- What right atrial structure develops from the sinus venosus?
- The smooth-walled part (sinus venarum)
- What right atrial structure develops from the primitive (embryonic) atrium?
- The rough, trabeculated right auricle
- What is the first septum to form within the primitive atrium?
- The septum primum
- What is the transient opening between the septum primum and the endocardial cushions, before it fuses, called?
- The ostium primum (foramen primum)
- As the ostium primum closes, what new opening forms from perforations in the septum primum?
- The ostium secundum
- What second atrial septum forms to the right of the septum primum?
- The septum secundum
- What is the opening in the septum secundum called?
- The foramen ovale
- An ostium primum atrial septal defect results from failure of which structures to fuse?
- The septum primum and the endocardial cushions
- An ostium primum ASD is classically associated with which condition?
- Down syndrome, as part of an AV septal defect
- The most common type of atrial septal defect results from excessive resorption of which structure?
- The septum primum, causing an ostium secundum ASD