Thyroid
The thyroid is one of the largest endocrine glands in the body. This gland is found in the throat. The thyroid controls how quickly the body burns energy, makes proteins, and how sensitive the body should be to other hormones.
The principal hormones it makes are thyroxine (T4) an triiodothyronine (T3), which is more active. These hormones regulate the growth of many systems in the body. T3 and T4 are synthesised from iodine and tyrosine. The thyroid also makes calcitonin, which plays a role in calcium homeostasis.
Diseases
Hyper- and hypofunction (affects about 2% of the population)
- Hypothyroidism (underactivity) - Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.
- Hashimoto's thyroiditis / thyroiditis
- Ord's thyroiditis
- Postoperative hypothyroidism
- Postpartum thyroiditis
- Silent thyroiditis
- Acute thyroiditis
- Iatrogenic hypothyroidism
- Hyperthyroidism (overactivity)
- Thyroid storm
- Graves-Basedow disease
- Toxic thyroid nodule
- Toxic nodular struma (Plummer's disease)
- Hashitoxicosis
- Iatrogenic hyperthyroidism
- De Quervain thyroiditis (inflammation starting as hyperthyroidism, can end as hypothyroidism)
Anatomical problems
- Goitre
- Lingual thyroid
- Thyroglossal duct cyst
Tumors
- Thyroid adenoma
- Thyroid cancer
- Papillary
- Follicular
- Medullary
- Anaplastic
- Lymphomas and metastasis from elsewhere (rare)
Deficiencies
Additional images
Sagittal section of nose mouth, pharynx, and larynx.
Diagram showing common arrangement of thyroid veins.
Section of thyroid gland of sheep. X 160.
Thyoid histology
Thyroid Media
The thyroid gland surrounds the cricoid and tracheal cartilages and consists of two lobes. This image shows a variant thyroid with a pyramidal lobe emerging from the middle of the thyroid.
Clear pyramidal lobe (center) as viewed from the front
Floor of pharynx of embryo between 35 and 37 days after fertilization.
The thyroid hormones T3 and T4 have a number of metabolic, cardiovascular and developmental effects on the body. The production is stimulated by release of thyroid stimulating hormone (TSH), which in turn depends on release of thyrotropin releasing hormone (TRH).
Synthesis of the thyroid hormones, as seen on an individual thyroid follicular cell:*- Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis.*- Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I−) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms. *- This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner.*- In the colloid, iodide (I−) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase.*- Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues).*- In conjugation, adjacent tyrosyl residues are paired together.*- The entire complex re-enters the follicular cell by endocytosis.*- Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules, which enters the blood by largely unknown mechanisms.
The thyroid was named by Thomas Wharton after the ancient Greek shield of a similar pronunciation. Shown is an example of such a shield, as engraved on a coin dating from 431 to 424 BCE.
Related pages
Other websites
- American Thyroid Association (Thyroid Information and professional organization)
- New Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer[dead link] from the American Thyroid Association Taskforce.
- Thyroid Disease Manager (free online textbook)
- Thyroid Disease (Nuclear Medicine Information)
- The Thyroid Foundation of America (Education about Thyroid Disease)
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