Thyroid hormones

Thyroid hormones are iodinated hormones produced by the thyroid gland, chiefly thyroxine (T4) and triiodothyronine (T3). They regulate metabolism, growth, and development.

Thyroid hormone synthesis: The production and release of T4 and T3 by thyroid follicular cells. This pathway joins iodine uptake to the gland’s release of its principal hormones.
Thyroxine: The four-iodine thyroid hormone T4, which circulates abundantly and can be converted into T3. T4 is the main hormone released by the thyroid and a major precursor of T3.
Thyroid function tests: Blood tests, especially TSH and free T4 measurements, used to assess thyroid function. These measurements infer whether hormone production and feedback are appropriately balanced.
Hypothyroidism: A state in which thyroid-hormone production or action is insufficient for the body’s needs. It shows the metabolic and developmental effects of too little thyroid-hormone activity.
Steroid hormone: A lipid-derived hormone that typically signals through intracellular receptors. Like thyroid hormones, steroid hormones can regulate transcription through intracellular receptors, but have different chemistry.
Thyroid peroxidase: An enzyme that oxidizes iodide and catalyzes iodination and coupling reactions in thyroid-hormone synthesis. It performs the chemical steps that attach iodine and assemble hormone precursors.
Triiodothyronine: The three-iodine thyroid hormone T3, the more potent ligand for thyroid hormone receptors. T3 supplies much of the receptor activity attributed to thyroid hormones.
Levothyroxine: A synthetic form of T4 used chiefly to replace deficient thyroid hormone. It restores hormone supply and relies partly on conversion to T3 in tissues.
Hyperthyroidism: A state in which the thyroid gland produces excessive thyroid hormone. It demonstrates the systemic effects of sustained excess hormone production.
Catecholamine: A class of tyrosine-derived signaling molecules that includes adrenaline, noradrenaline, and dopamine. Catecholamines share an amino-acid origin but usually act through faster cell-surface signaling.

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