Thyroid hormones
Thyroid hormones are produced by thyroid glands. T3 and T4 are thyroid hormones that are made up of iodine and tyrosine.[1] Less intake of iodine results in less production of T3 and T4 which may lead to a medical condition called hypothyroidism. Greater production of thyroid hormones leads to hyperthyroidism.[2]
Function
Thyroid hormones control the metabolism of the body. They act to increase the production of proteins, basal metabolic rate and growth hormone.
Thyroid Hormones Media
Synthesis of the thyroid hormones, as seen on an individual thyroid follicular cell:[page needed]*- 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.*- Thyroglobulin re-enters the follicular cell by endocytosis.*- Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules*- Efflux of thyroxine and triiodothyronine from follicular cells, which appears to be largely through monocarboxylate transporter (MCT) 8 and 10, and entry into the blood.
