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Skip Navigation. Top of the page. Thyroid Hormone Production and Function. Overview The thyroid gland uses iodine from food to make two thyroid hormones : triiodothyronine T3 and thyroxine T4. When the hypothalamus and pituitary are working normally, they sense when: Thyroid hormone levels are low, so they secrete more TRH and TSH.
This stimulates the thyroid to make more hormones. This reduces hormone production by the thyroid. How do thyroid hormones work? They: Control the rate at which your body burns calories your metabolism.
The thyroid gland is part of the hypothalamic-pituitary-thyroid axis, and control of thyroid hormone secretion is exerted by classical negative feedback, as depicted in the diagram.
Thyroid-releasing hormone TRH from the hypothalamus stimulates TSH from the pituitary, which stimulates thyroid hormone release. As blood concentrations of thyroid hormones increase, they inhibit both TSH and TRH, leading to "shutdown" of thyroid epithelial cells. Later, when blood levels of thyroid hormone have decayed, the negative feedback signal fades, and the system wakes up again.
They: Regulate the rate at which calories are burned, affecting weight loss or weight gain. Can slow down or speed up the heartbeat. Can raise or lower body temperature. Influence the rate at which food moves through the digestive tract. Control the way muscles contract. Control the rate at which dying cells are replaced.
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