The thyroid is a butterfly-shaped endocrine gland located in the anterior neck, spanning vertebrae C5 to T1, just below the laryngeal prominence (Adam's apple). It consists of two lobes (left and right) connected by an central isthmus that lies over the second and third tracheal rings. Weighing approximately
g, the gland regulates metabolism and calcium homeostasis via follicular cells and C-cells, respectively.
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Anatomical Structure and Location
- Lobes: The right and left lobes are generally symmetrical, often possessing a pyramidal lobe (a remnant of embryological development) extending upward.
- Isthmus: Connects the two lobes across the trachea.
- Location: Situated within the visceral compartment of the neck, deep to the strap muscles (sternothyroid and sternohyoid) and anterior to the trachea.
Connections: Anchored to the trachea by the lateral suspensory ligament (Berry ligament).
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Blood Supply and Innervation
- Arterial Supply: Highly vascular, receiving blood from the superior thyroid arteries (branches of the external carotid artery) and inferior thyroid arteries (branches of the thyrocervical trunk).
- Venous Drainage: Accomplished via superior, middle, and inferior thyroid veins.
Nerves: Closely related to the recurrent laryngeal nerves (which lie in the tracheoesophageal groove) and external branches of the superior laryngeal nerves.
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Histological and Developmental Features
Follicular Cells: Produce triiodothyronine (
) and thyroxine (
- C-cells (Parafollicular Cells): Produce calcitonin to reduce serum calcium.
- Development: Develops from the base of the tongue (foramen cecum) during the third week of gestation and descends to the neck