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Triiodothyronine (T3) is a thyroid hormone that affects almost every physiological process in the body, including metabolism, growth, and heart rate. It is produced from thyroxine (T4) by deiodinase enzymes, and its level is regulated by thyroid-stimulating hormone (TSH) in a feedback loop.
Hypothyroidism is a condition where the thyroid gland does not produce enough thyroid hormones, which can affect various body functions and cause symptoms such as fatigue, weight gain, and depression. Learn about the common causes, such as iodine deficiency and Hashimoto's thyroiditis, how to diagnose it with blood tests, and how to treat it with levothyroxine.
Learn about the thyroid hormones T3 and T4, their roles in regulating metabolism, growth, and development, and how they are used to treat hypothyroidism. Find out how thyroid hormones are produced, transported, and degraded in the body, and what factors affect their synthesis and action.
TFTs are blood tests used to check the function of the thyroid. They include thyroid hormones such as TSH, T4, T3, and free T4 and T3, and may be affected by various factors such as pregnancy, medications, and circadian rhythm.
A medical condition present at birth marked by impaired physical and mental development, due to insufficient thyroid hormone caused by insufficient dietary iodine. Also known as endemic cretinism, it is one cause of congenital hypothyroidism, and can be prevented by iodine supplementation and newborn screening.
The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland. [2]
Euthyroid sick syndrome is a condition where thyroid hormone levels are abnormal, but the thyroid gland is not dysfunctional. It can occur in various acute and chronic illnesses, and is associated with altered deiodinase activity, hypothalamic-pituitary-thyroid axis, cytokines, and thyroid hormone receptors.
The Wolff–Chaikoff effect is known as an autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. [6] This becomes evident secondary to elevated levels of circulating iodide.