An endocrine organ, so named because it resembles a shield. It is principally concerned with the production of the thyroid hormones, thyroxine (often denoted as T4) and triiodothyronine (T3). The gland also produces calcitonin (from interstitial C-cells between the thyroid globules) which has a limited role in calcium homeostasis.
Embryology of the thyroid
The thyroid gland develops on the developing tongue from endoderm at the foramen cecum. From this position at the base of the tongue, it descends to its normal location through the thyroglossal duct, which normally degenerates by the end of the fifth week, leaving only the foramen cecum as a small depression at the back of the tongue. The thyroid gland continues to descend until the seventh week. If the duct fails to completely degenerate, thyroglossal cysts remain. If it fails to degenerate at all, the result is a persistent thyroglossal duct. Rarely, ectopic thyroid tissue needs (ideally referenced) indication of frequency may be found at any point along the former course of the thyroglossal duct. Thyroglossal cysts and ectopic thyroid tissue are associated conditions. Studies have shown that the gland starts to function in the tenth to twelfth week.
The thyroid is situated anteriorly at the base of the neck, although it can extend retrosternally. It consists of two lobes connected by an isthmus. In a variable proportion of people (12%, 55%, 60-65%), there is a pyramidal lobe (sometimes known eponymously as Lalouette's pyramid), which is regarded as some by an embryonal remnant of thryoid within the thyroglossal duct. In keeping with this embryological origin, the pyramidal lobe extends superiorly, usually from around the isthmus towards the hyoid bone.
A grossly enlarged thyroid is known as a goitre.
- See Thyroid hormones
Thyroid function tests
Guidance is available:
- Association for Clinical Biochemistry, British Thyroid Association, British Thyroid Foundation. UK Guidelines for the Use of Thyroid Function Tests. 2006
- ↑ Geraci G, Pisello F, Li Volsi F, Modica G, Sciumè C. The importance of pyramidal lobe in thyroid surgery. Il Giornale di chirurgia. 2008 Nov-Dec; 29(11-12):479-82.
- ↑ Braun EM, Windisch G, Wolf G, Hausleitner L, Anderhuber F. The pyramidal lobe: clinical anatomy and its importance in thyroid surgery. Surgical and radiologic anatomy : SRA. 2007 Feb; 29(1):21-7.(Link to article – subscription may be required.)
- ↑ Blumberg NA. Observations on the pyramidal lobe of the thyroid gland. South African medical journal = Suid-Afrikaanse tydskrif vir geneeskunde. 1981 Jun 20; 59(26):949-50.
- ↑ Association for Clinical Biochemistry, British Thyroid Association, British Thyroid Foundation. UK Guidelines for the Use of Thyroid Function Tests. 2006. Last accessed 2011 (Dec 11)