Embryology USMLE Step 1 Practice Question
A 4-year-old boy presents with recurrent lower respiratory tract infections and a chronic productive cough with foul-smelling sputum. Vital signs show temperature 38.2°C, heart rate 102/min, respiratory rate 26/min, and oxygen saturation 94% on room air. High-resolution CT chest reveals situs inversus totalis, bronchiectasis, and centrally located liver. Nasal endoscopy demonstrates immotile cilia. Immunoglobulin levels are normal. Which embryologic process is disrupted in this condition?
Answer choices
- AEndoderm-derived respiratory diverticulum budding
- BNodal signaling and establishment of left-right asymmetryCorrect answer
- CNeural crest cell migration to cardiac outflow tract
- DLateral plate mesoderm folding and body cavity formation
- EMesenchymal condensation in limb bud development
- FDynein arm assembly and axonemal structure formation
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