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Topic 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, which stimulates the thyroid to make more hormones. Thyroid hormone levels are too high, so they secrete less TRH and TSH, which reduces hormone production by the thyroid.
If a person has too little thyroid stimulating hormone, it is most likely that their thyroid gland is making too much thyroid hormone, that is, they have an overactive thyroid or hyperthyroidism , which is suppressing the thyroid stimulating hormone. People with an overactive thyroid have the opposite symptoms to those with hypothyroidism, i.
They may also have a slightly enlarged thyroid gland. Treatment is medication in the form of tablets, which reduce the activity of the thyroid gland and return all thyroid hormone levels to normal. Rarely, problems in the pituitary gland can also result in a low thyroid stimulating hormone, and low free thyroid hormone levels. About Contact Events News.
Search Search. You and Your Hormones. Students Teachers Patients Browse. Human body. Students Teachers Patients Browse. Human body. Home Hormones Thyrotropin-releasing hormone. Thyrotropin-releasing hormone Thyrotropin-releasing hormone is produced by the hypothalamus. It plays an important role in the regulation of thyroid gland activity. Alternative names for thyrotropin-releasing hormone Thyrotrophin-releasing hormone; TRH What is thyrotropin-releasing hormone?
How is thyrotropin-releasing hormone controlled? What happens if I have too much thyrotropin-releasing hormone? There is no known case of too much thyrotropin-releasing hormone.
What happens if I have too little thyrotropin-releasing hormone? Thyroid hormones T4 and T3 are produced by the follicular cells of the thyroid gland and regulated by thyroid-stimulating hormone TSH.
The thyroid hormones thyroxine T4 and triiodothyronine T3 are produced from thyroid follicular cells within the thyroid gland, a process regulated by the thyroid-stimulating hormone secreted by the anterior pituitary gland. Thyroglobulin, the pre-cursor of T4 and T3, is produced by the thyroid follicular cells before being secreted and stored in the follicular lumen. Iodide is actively absorbed from the bloodstream by a process called iodide trapping. In this process, sodium is co-transported with iodide from the basolateral side of the membrane into the cell, and then concentrated in the thyroid follicles to about thirty times its concentration in the blood.
Through a reaction with the enzyme thyroperoxidase, iodine is bound to tyrosine residues in the thyroglobulin molecules to form monoiodotyrosine MIT and diiodotyrosine DIT. 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.
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