The parafollicular (C) cells of the thyroid originate from which structure?

• A. Ultimobranchial body from the fourth pouch
• B. Superior parathyroid from the fourth pouch
• C. Thymus from the third pouch
• D. Inferior parathyroid from the third pouch

Answer: (A)

Parafollicular (C) cells come from neural crest–derived cells that migrate into the ultimobranchial body, an outgrowth tied to the ventral part of the fourth pharyngeal pouch. This ultimobranchial body later fuses with the developing thyroid, and its cells differentiate into the C cells that sit between follicles and secrete calcitonin. In contrast, structures from the third pouch give thymus and inferior parathyroids, while the fourth pouch contributes the superior parathyroids and, via the ultimobranchial body, the C cells. So the origin of the parafollicular cells is the ultimobranchial body from the fourth pharyngeal pouch.