Thyroid

Thyroid
The human thyroid (tan), as viewed from the front; and arteries (red) supplying the gland.
The thyroid gland is a butterfly-shaped gland located in the neck below the Adam's apple.
Details
Pronunciation	/ˈθaɪrɔɪd/
Precursor	Thyroid diverticulum (an extension of endoderm into 2nd pharyngeal arch)
System	Endocrine system
Artery	Superior, inferior thyroid arteries
Vein	Superior, middle, inferior thyroid veins
Identifiers
Latin	glandula thyreoidea
Greek	θυρεοειδής
MeSH	D013961
TA98	A11.3.00.001
TA2	3863
FMA	9603
Anatomical terminology [edit on Wikidata]

The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans, it is a butterfly-shaped gland located in the neck below the Adam's apple. It consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the isthmus (pl.: isthmi). Microscopically, the functional unit of the thyroid gland is the spherical thyroid follicle, lined with follicular cells (thyrocytes), and occasional parafollicular cells that surround a lumen containing colloid.

The thyroid gland secretes three hormones: the two thyroid hormones – triiodothyronine (T₃) and thyroxine (T₄) – and a peptide hormone, calcitonin. The thyroid hormones influence the metabolic rate and protein synthesis and growth and development in children. Calcitonin plays a role in calcium homeostasis.^[1]

Secretion of the two thyroid hormones is regulated by thyroid-stimulating hormone (TSH), which is secreted from the anterior pituitary gland. TSH is regulated by thyrotropin-releasing hormone (TRH), which is produced by the hypothalamus.^[2]

Thyroid disorders include hyperthyroidism, hypothyroidism, thyroid inflammation (thyroiditis), thyroid enlargement (goitre), thyroid nodules, and thyroid cancer. Hyperthyroidism is characterized by excessive secretion of thyroid hormones: the most common cause is the autoimmune disorder Graves' disease. Hypothyroidism is characterized by a deficient secretion of thyroid hormones: the most common cause is iodine deficiency. In iodine-deficient regions, hypothyroidism (due to iodine deficiency) is the leading cause of preventable intellectual disability in children.^[3] In iodine-sufficient regions, the most common cause of hypothyroidism is the autoimmune disorder Hashimoto's thyroiditis.