Embryology Questions Medical School (1000+ Tested)

| Mechanism | Defect | Clinical pearl | |-----------|--------|----------------| | Failure of endocardial cushion fusion (neural crest cells) | (ostium primum ASD + VSD + cleft mitral valve) | Associated with Down syndrome (40% of Down patients have AV canal). | | Abnormal conotruncal septation (neural crest migration failure) | Transposition of great arteries (TGA), Tetralogy of Fallot (TOF), Truncus arteriosus | TOF = VSD, overriding aorta, RVH, pulmonary stenosis. Boot-shaped heart. TGA = cyanosis day 1, needs prostaglandins to keep PDA open. | | Failure of spiral septum rotation | Dextro-TGA (aorta from RV, pulmonary from LV) | Incompatible with life unless mixing (ASD/VSD/PDA). | | Abnormal ductus arteriosus closure | Patent ductus arteriosus (PDA) | Machine-like murmur. Associated with rubella (also cataracts, deafness, PDA). |

Dextrocardia (heart on right) with situs inversus is not a heart defect per se – it’s a laterality defect from ciliary dysfunction (Kartagener). Dextrocardia with situs solitus is a severe heart malformation. 4. Foregut & Midgut Rotation – The “Malrotation & Volvulus” Danger The embryology: Midgut herniates at week 6, rotates 270° counterclockwise, returns at week 10. Embryology Questions Medical School

Kartagener syndrome (immotile cilia) causes situs inversus, but that's not an NTD. 2. Pharyngeal Arches – The “Cranial Nerve & Artery” Matrix The embryology: Six arches (though 5th regresses). Each arch has its own: Cartilage (bone), Nerve, Artery, Muscle. | Mechanism | Defect | Clinical pearl |