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326 SEcTion iii EndocrinE ` endocrine—embryology EndocrinE ` endocrine—AnAtomy

` endocrine—embryology

Thyroid development Thyroid diverticulum arises from floor of primitive pharynx and descends into neck. Connected to
A tongue by thyroglossal duct, which normally disappears but may persist as cysts or the pyramidal
lobe of thyroid. Foramen cecum is normal remnant of thyroglossal duct.
Most common ectopic thyroid tissue site is the tongue (lingual thyroid). Removal may result in
hypothyroidism if it is the only thyroid tissue present.
Thyroglossal duct cyst A presents as an anterior midline neck mass that moves with swallowing
or protrusion of the tongue (vs persistent cervical sinus leading to pharyngeal cleft cyst in lateral
neck).
Thyroid follicular cells derived from endoderm.

Foramen cecum
Hyoid bone
Thyrohyoid membrane
Internal carotid artery
Thyroglossal duct
External carotid artery
Thyroid cartilage
Superior thyroid artery
Thyroid Inferior thyroid artery

Trachea
Left subclavian artery
Brachiocephalic artery

FAS1_2019_08-Endocrine.indd 326 11/7/19 4:30 PM