The Pharyngeal Apparatus Practice Test

DiGeorge syndrome reflects a problem with the development of the structures derived from the third and fourth pharyngeal pouches during early embryogenesis. The most striking features—thymic aplasia and hypoparathyroidism—arise because the thymus and the inferior parathyroids come from those pouches. A 22q11.2 deletion disrupts neural crest cell migration into these pharyngeal regions, leading to maldevelopment and the characteristic immunologic and calcium-regulation problems, often with heart defects as part of the broader outflow tract anomalies. The other arches contribute to different head and neck structures, so their maldevelopment wouldn’t explain the specific combination of thymic and parathyroid deficiencies seen in DiGeorge. Thus, the best association is the third and fourth pharyngeal pouches (often discussed as related arches in exam contexts).