Thyroxine is produced by the thyroid gland , which stimulates the basal metabolic rate. It controls the speed at which oxygen and food products react to release energy for the body to use. Thyroxine plays an important role in growth and development.
Thyroxine levels are controlled by negative feedback. Linking two moieties of DIT produces T4. Proteases digest iodinated thyroglobulin, releasing the hormones T4 and T3, the biologically-active agents central to metabolic regulation. T3 is identical to T4, but it has one less iodine atom per molecule. T4 is believed to be a pro-hormone and a reservoir for the more active and main thyroid hormone T3.
T4 is converted as required in the tissues by iodothyronine deiodinase. Thyroid hormone : Diagrammatic representation of thyroid hormone synthesis in a thyroid follicle. If there is a deficiency of dietary iodine, the thyroid will not be able to make thyroid hormone. A lack of thyroid hormone will lead to decreased negative feedback on the pituitary, which in turn, will lead to increased production of thyroid-stimulating hormone, which causes the thyroid to enlarge goiter.
The primary function of the thyroid is to produce the hormones triiodothyronine T3 , thyroxine T4 , and calcitonin. Triiodothyronine T3 and thyroxine T4 are enzymes produced by the thyroid gland. T4 is thought to be a pro-hormone to the more metabolically active T3. T4 is converted to T3 in tissues as required by deiodinase enzymes. Calcitonin is another hormone released by the thyroid gland that is responsible for modulating blood calcium levels in conjunction with parathyroid hormone, which is released from the parathyroid.
The main activity of the thyroid hormones T3 and T4 is to boost the basal metabolic rates of proteins, fats, and carbohydrates as well as vitamins. Thyroid system : An overview of the thyroid system. Thyroid hormones affect the dilation of blood vessels, which in turn affects the rate at which heat can escape the body. The more dilated blood vessels are, the faster heat can escape. A person who suffers from hyperthyroidism an over-active thyroid will experience a fever; conversely, a person who suffers from hypothyroidism a less active thyroid will experience a decrease in body temperature.
The cells of the developing brain are a major target for T3 and T4. See the article on hypothyroidism for more information. About Contact Events News. Search Search. You and Your Hormones. Students Teachers Patients Browse. Human body. Home Hormones Thyroxine. Thyroxine Thyroxine is the main hormone secreted into the bloodstream by the thyroid gland. It plays vital roles in digestion, heart and muscle function, brain development and maintenance of bones. The hypothalamus releases thyrotropin-releasing hormone TRH , which stimulates the pituitary gland to release thyroid-stimulating hormone TSH.
When the hypothalamus and pituitary are working normally, they sense when:. See a picture of thyroid hormone production. Author: Healthwise Staff. This information does not replace the advice of a doctor.
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