What is the embryological origin of the thyroid gland?

The thyroid gland originates from a midline endodermal diverticulum called the thyroglossal duct, which forms from the floor of the primitive pharynx. Its adult remnant is the foramen cecum on the tongue.

How does the thyroglossal duct develop into the thyroid gland?

During the 3rd week of development, the thyroglossal duct grows downward from the pharynx, travels anterior to the hyoid bone, and curls around it. By the 7th week, it bifurcates to form the two lobes and isthmus, then regresses, leaving only the foramen cecum.

What are parafollicular (C) cells, and where do they come from?

Parafollicular (C) cells are thyroid cells that produce calcitonin. They are derived from neural crest cells that migrate into the caudal pharyngeal complex, specifically the ultimobranchial body formed by the 4th and 5th pharyngeal pouches.

What are some common clinical anomalies related to thyroid development?

Common anomalies include thyroglossal cysts/fistulas (midline neck cysts from duct remnants), ectopic thyroid tissue (found in places like the tongue or chest), and anomalous lobes (such as a pyramidal lobe or absent isthmus).

What is a thyroglossal cyst, and why does it occur?

A thyroglossal cyst is a midline neck cyst that forms from remnants of the thyroglossal duct that fail to regress completely. It often appears by age 5 and can rupture to form a fistula.

When does the thyroid gland start producing hormones during development?

By the 12th week of development, follicular cells begin producing colloid (source of T3 and T4), and parafollicular cells start secreting calcitonin.

What is the pyramidal lobe of the thyroid?

The pyramidal lobe is an anomalous lobe of the thyroid that may persist in about half the population. It often lies on the left side and can be connected to the hyoid bone by fibromuscular tissue called the levator glandulae thyroideae.

Thyroid Development – Thyroglossal Duct

❓ Frequently Asked Questions