Thyroid hormones (from the thyroid glandula thyroidea , i.e. thyroid hormones) – T4 and T3 are intended in the body to control basal metabolism. If too much of them is synthesized and enters the bloodstream, then the metabolism increases, but if there are few of these hormones, the metabolism in the body slows down.  

T4 hormone (thyroxine, tetraiodothyronine ) is the main thyroid hormone, making up 90% of the hormones produced by the gland. The number “four” in its name appears due to the fact that the molecule of the hormone thyroxine includes four atoms of iodine. 

The T3 hormone (triiodothyronine) is the second thyroid hormone. Its activity is 10 times higher than that of thyroxine. 10% of the T3 hormone is secreted by the cells of the thyroid gland, and the remaining 90% are formed in all tissues of the human body from thyroxine by the “detachment” of one atom of iodine. After removing this “extra” atom, the T4 hormone turns 10 times more active T3. It is triiodothyronine that has all the main effects of thyroid hormones. 

The third, little-talked about hormone produced by the thyroid gland is calcitonin . It regulates the exchange of calcium and phosphorus. This hormone provides bone strength by saturating it with calcium and preventing bone breakdown. It is also a tumor marker for medullary thyroid cancer. 

Thyroid stimulating hormone (TSH) is a hormone from the pituitary gland, not the thyroid gland as many think. But he has a huge role in the work of the thyroid gland, as he controls its work. The regulation of synthesis with the participation of the pituitary gland and the hypothalamus ensures the flow of optimal amounts of thyroid hormones into the blood. The connection between the pituitary gland and the work of the thyroid gland is like a “swing” – if there is a lot of TSH, then the amount of thyroid hormones decreases and vice versa, if TSH is little, the amount of T4 and T3 increases. 

Of course, abnormally high or abnormally low levels of thyroid hormones lead to disease. But we will talk about these diseases in the following articles.