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How does the thyroid gland regulate the body's metabolism?

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Color-enhanced electron micrograph showing yellow mitochondria and blue endoplasmic reticulum within magenta-stained hepatocyte liver cells at high magnification. — Metabolism Electron micrograph of hepatocyte cells showing mitochondria (yellow). The primary function of mitochondria is to generate large quantities of energy in the form of ATP, which captures chemical energy from the metabolic breakdown of food molecules.

The thyroid gland regulates metabolism by producing and secreting thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3). These hormones are synthesized from iodine and tyrosine within the thyroid follicles. Thyroid-stimulating hormone (TSH) from the pituitary gland stimulates the thyroid to release these hormones.123

Once in the bloodstream, T3 is the more active form, entering cells and binding to nuclear receptors. This binding increases the transcription of DNA, leading to the synthesis of proteins that regulate nutrient utilization and oxygen consumption by mitochondria. Essentially, thyroid hormones increase the rate at which cells produce energy and dissipate heat, influencing carbohydrate and lipid metabolism, and stimulating the central nervous system. This overall effect is a significant increase in the body's metabolic rate.14