Triiodothyronine

Triiodothyronine, or T3, is an iodine-containing thyroid hormone that regulates gene expression and influences metabolism, growth, and development.

Thyroxine: Thyroxine, or T4, is an iodine-containing thyroid hormone that serves largely as a precursor to T3. T4 supplies much of the T3 made outside the thyroid gland.
Thyroid gland: An endocrine gland in the neck that produces thyroid hormones and calcitonin. It secretes T3 directly and produces most circulating T4.
Thyroid function tests: Blood tests that assess thyroid activity, commonly by measuring TSH and thyroid hormones. T3 measurements help evaluate suspected thyroid dysfunction in selected cases.
Basal metabolic rate: The rate of energy expenditure by the body at rest under standardized conditions. T3 raises metabolic activity in many tissues and can increase resting energy use.
Deiodinase: A family of enzymes that removes iodine atoms from thyroid hormones. Deiodinases convert T4 into active T3 or inactivate thyroid hormones.
Iodine: A chemical element required for thyroid hormone synthesis. T3 contains three iodine atoms, making iodine supply essential to its production.
Hyperthyroidism: A condition in which excessive thyroid hormone activity accelerates many bodily processes. Excess T3 can produce the metabolic and cardiovascular effects of thyroid overactivity.
Thermogenesis: The production of heat by living organisms. T3 promotes heat production by influencing cellular energy metabolism.
Thyroid hormone receptor: A nuclear receptor protein that binds thyroid hormones and regulates gene transcription. T3 binds these receptors to alter expression of target genes.
Thyroglobulin: A large protein in thyroid follicles that provides the scaffold for thyroid hormone synthesis and storage. The thyroid builds hormone precursors from iodine attached to thyroglobulin.

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