Triiodothyronine or T3 is a metabolically active hormone produced by the thyroid and the T3 hormone function is associated with almost all processes in the human body. It is the most powerful hormone produced by the thyroid and its functions are associated with the body temperature, growth and heart rate. In comparison with the other thyroid hormone, T4 or thyroxine, T3 is produced in a smaller quantity and it contains fewer iodine atoms per molecule. The production of both T3 and T4 are activated by the thyroid stimulating hormone or the TSH. Actually, after the deiodination of T4 in the thyroid, thyroxine is converted to T3, hormone which will inhibit THS. Thyroid t3 hormones have a biological half-life up to 2 days and a half.
There are two types of T3 thyroid hormones. The first one, called type I is found in the liver and the second, type II, is found in the pituitary. Both thyroid hormones, T3 and T4, bind to thyroid receptors which are in fact nuclear receptors. Due to the fact that the hormones are not lipophilic, they cannot pass through the phospholipid layers. Thus, they pass into the cells with the help of specific transport proteins. The response elements in gene promoters which are connected to the thyroid’s receptors will enable them to either activate, either inhibit the transcription. The thyroid receptors are also the ones that modulate a tissue’s sensitivity to T3.
T3 hormone is responsible for increasing the consumption of both oxygen and energy in the body, due to the fact that it increases the minimal level of calories that a person needs in order to sustain life while resting. This hormone is also responsible for increasing the synthesis and degradation of the endogenous macromolecules and it affects most of the tissues of the body, excepting the spleen and testicles. By stimulating the production of RNA polymerase, T3 hormones increase the rate of protein degradation and synthesis. There are cases when the rate of protein synthesis is exceeded by the rate of protein degradation and as a result, the body is most likely to go into negative ion balance. T3 hormones increase as well the rate of glycogen degradation and the one of glucose synthesis. This type of thyroid hormone has a role in the breakdown of cholesterol, since it stimulates it. A very important function of T3 hormones is related to the cardiovascular system, they being able to increase the heart rate and its force of contraction. As a result, the systolic blood pressure is increased and the diastolic blood pressure is decreased. It is very important in the development of the embryo, influencing the growth of the central nervous system after birth and it has important effects in the growth of bones.
The T3 hormone function is what makes this type of hormone so important for a healthy body.