Total T4 (thyroxine)
The T4 affects almost every organ except the spleen and testicles. Thyroxine increases heart rate and blood pressure. The rate of protein creation, the rate of glucose and fat (cholesterol) "burning" are accelerated, the inner layer of the uterus (endometrium) in women thickens. The body temperature rises. The hormone is responsible for growth and development of the body - the central nervous system and bone structure. The biological activity is much lower than that of T3, but the elimination time and concentration are much higher.
T4 has a peculiarity: under the influence of certain enzymes, it is converted into a more active form of the hormone, T3.
The amount of T4 is directly related to iodine levels and TTH (see thyroid hormone).
The hormone affects behaviour: its increase leads to increased activity, short temper, violent mood swings and a tendency to have hysterical seizures. T4 deficiency in the body manifests itself as lethargy, tendency to tearfulness and depression, lethargy.
Total T4 includes two fractions: bound and free. It is reasonable to determine both total and free active T4, as there may be states in which free T4 is reduced or increased while the total T4 level is normal. Therefore, thyroid function is impaired.