Question
The thyroid gland originates from:
| A. |
A. Second pharyngeal pouch
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| B. |
B. Third pharyngeal pouch
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| C. |
C. Floor of the primitive pharynx
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| D. |
D. Fourth pharyngeal pouch
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Show Answer
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Correct Answer » C
Explanation
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Development of the Thyroid Gland
- Origin: Endoderm of the floor of the primitive pharynx.
- Initial site: Near the foramen cecum of the tongue.
- Descent: Thyroid descends in the midline in front of the pharynx and larynx.
- Connection during descent: Thyroglossal duct.
- Normal remnant: Foramen cecum.
- Thyroid follicular cells: Endodermal origin.
- Parafollicular/C cells: Derived from neural crest cells associated with the ultimobranchial body.
- Clinical correlation:
- Persistent thyroglossal duct → thyroglossal cyst.
- Ectopic thyroid tissue can occur anywhere along the path of descent.
- Lingual thyroid is the commonest form of ectopic thyroid tissue.
- Parathyroid derivatives:
- Third pouch → inferior parathyroids + thymus
- Fourth pouch → superior parathyroids
