Embryology USMLE Step 1 Practice Question
During anatomy laboratory, a first-year medical student is dissecting the atrial chambers of the heart. At the upper border of the fossa ovalis, she discovers a small opening through which the tip of her probe can be passed from the right into the left atrium. The laboratory instructor identifies this as a probe patency of the atrial septum. This probe patency resulted from which of the following developmental events?
Answer choices
- AFailure of the endocardial cushions to form
- BFailure of postnatal fusion of septum primum and septum secundumCorrect answer
- CExcessive resorption of the septum primum
- DFailure of the septum primum to fuse with the endocardial cushions
- EFailure of the right and left conotruncal ridges to fuse
- FFailure of the interventricular foramen to close during embryonic development
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