With its presence, TSH promotes the absorption of iodine and the release of the hormones triiodothyronine (T3) and thyroxine (T4) in the bloodstream.
Also called thyroid stimulating hormone, thyrotropic hormone, or thyrotropin, TSH is produced by the anterior pituitary (a small gland located at the base of the skull). In turn, the release of TSH from the pituitary is controlled by another hormone , produced and secreted by the hypothalamus, called TRH (or thyrotropin releasing hormone).
The secretion of thyrotropin is instead inhibited by circulating thyroid hormones: when the latter are present in the blood in adequate quantities, the pituitary gland slows down the production of TSH.
For this reason, the determination of the thyroid stimulating hormone is the first useful test to evaluate the functionality of the thyroid, not only when problems are suspected, but also for a routine check of the health of the gland itself.
In both cases, the hormones secreted by the thyroid act both directly at the level of the adenohypophysis and indirectly at the hypothalamic level. For this purpose, the regulatory mechanism is referred to as the hypothalamic-pituitary-thyroid axis, often illustrated for educational purposes as a clear example of negative feedback. .
A sharp drop in ambient temperature also causes the hypothalamus to increase the secretion of TRH, with increased plasma levels of TSH (thyroid hormones accelerate metabolism, hence the production of heat). If necessary, the hypothalamus can also slow down. the secretion of TSH through somatostatin.
Thyrotropic hormone acts in the thyroid gland, stimulating its growth and endocrine activity (biosynthesis and hormonal secretion). The hormones produced by this gland, both containing iodine, are called triiodothyronine (T3) and thyroxine (T4), which covers alone 90% of the secretion.
