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 | |
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.
- ^ Guyton & Hall 2011, p. 907.
- ^ Boron WF, Boulpaep EL (2012). Medical Physiology (2nd ed.). Philadelphia: Saunders. p. 1052. ISBN 978-1-4377-1753-2.
- ^ Harrison's 2011, pp. 2913, 2918.