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Hypothyroidism (also called underactive thyroid, low thyroid or hypothyreosis) is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormones. [3] It can cause a number of symptoms, such as poor ability to tolerate cold , extreme fatigue, muscle aches , constipation , slow heart rate , depression , and ...
The major form of thyroid hormone in the blood is thyroxine (T 4), whose half-life of around one week [4] is longer than that of T 3. [5] In humans, the ratio of T 4 to T 3 released into the blood is approximately 14:1. [6] T 4 is converted to the active T 3 (three to four times more potent than T 4) within cells by deiodinases (5′-deiodinase).
Liothyronine is the most potent form of thyroid hormone. Liothyronine sodium, a salt of triiodothyronine (T 3 ), is chemically similar and pharmacologically equivalent to T 3 . As such, it acts on the body to increase the basal metabolic rate, affect protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline) by ...
They inhibit release of thyroid hormones by the thyroid gland.The most studied drug in this class is lithium, which inhibits thyroid hormone secretion by inhibiting iodotyrosine coupling, thyroidal iodide uptake, and alteration in structure of thyroglobulin, [10] a protein which acts as a substrate for the synthesis of thyroid hormones and storage of inactive forms of T3, T4 and iodine within ...
Fasting in healthy, euthyroid people causes reduced T3 and elevated rT3, although TSH is usually unchanged. [3] [5] [10] Even moderate weight loss can lower T3. [2] This may be primarily via reduced levels of leptin (the satisfaction hormone). Low leptin levels can downregulate hypothalamic TRH neurons and cause a reduction in TSH.
Ions such as thiocyanate [7] (from cigarette smoking for example [8]) and perchlorate decrease iodide uptake by competitive inhibition and, as a consequence of reduced thyroxine and triiodothyronine secretion by the gland, cause, at low doses, an increased release of thyrotropin (by reduced negative feedback), which then stimulates the gland.
Thyroxine has a half-life of approximately one week and hence maintains relatively stable blood levels. Its production and release are controlled through a complex feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. This regulatory system ensures that optimal hormone levels are maintained. [4]
Levothyroxine, also known as L-thyroxine, is a synthetic form of the thyroid hormone thyroxine (T 4). [5] [8] It is used to treat thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. [5] It may also be used to treat and prevent certain types of thyroid tumors. [5] It is not indicated for weight loss. [5]