The thyroid gland is an essential organ whose functions include growth development, increased muscle gain, decreased fat storage, hormone production, increased metabolism and increased catecholamine effect, to name a few. Understanding where this organ originated, how it developed and which cells and structures contributed to its maturation, will help those interested in having a solid anatomical foundation, for it is in the embryological development that the key to our bodies logical layout can be found.
The foramen cecum invaginates and shows the first signs of the formation of the thyroid gland. As it develops, it migrates inferiorly until it reaches it final destination, adjacent to the larynx. Sometimes a remnant of the migration know as the thyroglossal duct is present. This duct connects the mature thyroid gland to the foramen cecum. This structure is derived from the fourth pharyngeal arch and the third and fourth pharyngeal pouches.
Anatomy and Histology
The thyroid consists of two adjacent lobes that are connected via an isthmus. The isthmus can sometimes develop into a third lobe, known as the pyramidal lobe. The thyroid gland is innervated by the vagus nerve or the tenth cranial nerve.
The cellular consistency of the thyroid gland is made up of follicular and parafollicular cells.
These two cells have different embryological origins. The follicular cells come from the endoderm, while the parafollicular cells are derived from the ultimobranchial body.
Developmental abnormalities of the thyroid gland arise from the pharyngeal pouch abnormalities. An ectopic thyroid is one of the most common anomalies.
This occurs when thyroid tissue is found anywhere along the path of migration from the foramen cecum and not with the thyroid as a whole in its final destination. It can often be the only tissue with follicular and parafollicular cells and the thyroid as a whole can be completely absent. These remnants are still susceptible to thyroid diseases. The most common locations listed in order from the greatest include:
- a lingual thyroid
- a sublingual thyroid
- a thyroglossal duct remnant
- a thyroid in the anterior mediastinum
- a prelaryngeal thyroid
- an intralingual thyroid
- an intratracheal thyroid
Adult Thyroid Diseases
Adult diseases of the thyroid include:
- Hashimoto’s thyroiditis