The synthesis of thyroid hormones depends on the availability of iodide, TSH stimulation, and tyrosine residues in thyroglobulin (TG). Thyroid hormones are extremely important and have various actions. They work on virtually every cell in the body to alter gene transcription. Like catecholamines, epinephrine, and norepinephrine, thyroid hormones are synthesized from the amino acid tyrosine.
The synthesis of thyroid hormones requires the iodination of tyrosine molecules and the combination of two iodized tyrosine residues. Insufficient or excessive production of these hormones has negative effects. Disorders associated with impaired thyroid hormone secretion are common.