Thyroxine Synthesis
The synthesis of thyroxine takes place in the thyroid gland. The thyroid gland absorbs iodine from the blood and transfers it to the so-called “thyroglobulin”. Thyreroglobulin is a chain-like protein found in the thyroid gland, which is the basis for the synthesis of thyroid hormones. When iodine is transferred, molecules with either three or four iodine atoms are formed. In the last step, parts of the protein chain are separated and, depending on the number of iodine atoms, the final hormones T3 (triiodothyronine) and T4 (tetraiodothyronine / thyroxine) are formed.
Regulation mechanism
Hormones, as messenger substances of the body, are responsible for the regulation of various processes. In order to control their effect, however, they are themselves subject to a very complex and sensitive regulatory mechanism. The origin is located in a central region of the brain, the “hypothalamus“.
This is where the hormone “TRH” (thyrotropin releasing hormone) is regularly produced. TRH is released into the blood and migrates to the next station of the regulatory circuit, the pituitary gland, or “hypophysis”. There it causes the release of another hormone, the “TSH” (thyroid-stimulating hormone), which is now released back into the blood and reaches its final destination, the thyroid gland.
TSH signals the thyroid gland to release thyroxine (T4) and triiodothyronine (T3), which are distributed in the body with the blood and can now produce their actual effect. However, the regulatory mechanism is not only possible in one direction, but also in the other. T3 and T4 have an inhibitory effect on both TRH and TSH. This mechanism is called “feedback inhibition” in medicine. The thyroid hormones thus provide feedback on how many hormones have already been secreted and thus prevent overproduction.
Hormone class
Thyroid hormones like thyroxine (T4) and triiodothyronine (T3) belong to the so-called “lipophilic” hormones, which means that they are fat-soluble. They differ from the water-soluble (hydrophilic) hormones in that they are poorly soluble in the blood and must therefore be bound to so-called transport proteins. Their advantage, however, is that they have a longer lifespan on the one hand, and on the other hand they can cross the likewise lipophilic cell membrane very easily and can transmit their signals directly to the DNA contained in the cell nucleus.
