The Pharyngeal Apparatus Practice Test

Which statement correctly describes the thyroid gland origin?

It originates as an invagination of endoderm at the foramen cecum of the tongue It originates from neural crest cells in the pharyngeal arches It originates from mesoderm in the thorax It originates from ectoderm at the stomodeum

Correct Answer:

It originates as an invagination of endoderm at the foramen cecum of the tongue

Explanation:

The thyroid gland begins as an endodermal outpouching from the floor of the primitive pharynx, right at the foramen cecum on the tongue. This endodermal invagination forms the thyroid primordium and then migrates down the neck, connected by the thyroglossal duct, to reach its final position. The key point is that the gland itself arises from endoderm; while parafollicular C cells later incorporate neural crest cells, the main origin of the thyroid tissue is endoderm. Options suggesting mesoderm in the thorax or ectoderm at the stomodeum don’t fit the established germ-layer origin of the thyroid.

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