Thyroxine is endogenous hormone produced in the thyroid gland. It is involved in many processes in the body.
What is thyroxine?
Schematic diagram showing the anatomy and structure of the endocrine (hormone) system. Click to enlarge. Thyroxine is stimulated by the hormone TSH (thyroid-stimulating hormone). TSH is not produced in the thyroid gland, but in the pituitary gland. Thyroxine occurs in the body in different forms, as T3 and T4. These different names are derived from the iodine atoms in the molecule – three or four in number. However, only T4 is formed directly in the thyroid gland; conversion to T3 occurs mainly through the liver, kidneys, and muscles. Thyroxine is released into the blood and is involved in carbohydrate-fat and protein metabolism. The cardiovascular system is also controlled by thyroxine. Other hormones are also dependent on thyroxine.
Production, formation, and manufacture
TSH controls the formation of thyroxine. When there is not enough thyroid hormone in the body, the pituitary gland releases TSH, sending a signal to the thyroid gland that thyroxine is needed. The thyroid gland then begins to produce or secrete thyroxine. The thyroid gland is able to store the thyroxine and, in an emergency, supply the body for about ten months without new production. There would still not be a shortage of thyroxine. As soon as there is enough thyroid hormone in the blood again, TSH is cut back and production is reduced. This is a delicate hormone cycle that can be disrupted by many factors. For the production of hormones, the thyroid gland needs iodine, which, however, is nowadays usually supplied in sufficient form through a wholesome diet and can be ingested. Thyroxine is needed for cardiovascular function. It controls the strength of the heart muscle and, as a result, the pulse rate. Heat regulation is dependent on thyroxine and is needed more in winter than in summer. Thyroxine is also crucially involved in sugar and fat metabolism. Together with other hormones, such as insulin, it ensures the breakdown of sugar and the storage or conversion of fat and carbohydrates. This has a decisive influence on whether the body stores these substances or can excrete them again. These processes take place primarily in the liver and to some extent in the intestines. A constant, normal body weight is thus very much linked to thyroid function. In the developmental phase, thyroxine is needed for the development of the brain and nerve functions. If major deficiencies occur during pregnancy, this can even lead to irreparable brain damage in the unborn child. Thyroxine can be taken in tablet form if the need arises. The drug ensures adequate levels of the hormone in the blood.
Diseases, ailments, and disorders
Infographic on the anatomy and location of the thyroid gland, and the symptoms of hyperthyroidism and hypothyroidism. Click image to enlarge. Deficiency or overproduction of thyroxine occurs when the thyroid gland is diseased. In very rare cases, a disease of the pituitary gland can also affect the production of the hormone. The thyroid gland is relatively often affected by hyper- or hypofunction. There may be enlargement, but also atrophy of the thyroid gland. A simple change in the thyroid tissue can have a lasting effect on hormone production (for example, so-called cold nodules). However, autoimmune diseases, such as Hashimoto’s thyroiditis, in which various proteins responsible for the production of thyroxine are attacked, are often behind a deficient production of thyroxine due to a triggered underactivity of the thyroid gland. Graves’ disease also belongs to the autoimmune diseases, but in this case there is an overactivity of the thyroid gland – thus an excess of thyroxine. Sometimes the hyper- or hypothyroidism is also due to malignant changes. A hormonal imbalance of thyroxine can basically be detected first by an increase or decrease of the normal values of TSH in the blood. Further examinations provide information about the exact cause. Thyroxine is administered in tablet form in the case of hypothyroidism.There are dose strengths from 25 to 200 micrograms, and the dose must be adjusted in many cases. In individual cases, the administration of simple iodine is conceivable. However, this is out of the question in autoimmune disease, because the iodine stimulates the thyroid gland again and the autoimmune process is stimulated first, so that the intake of normal iodine is to be reduced and the already converted thyroxine is used, which no longer has to be processed by the thyroid gland and relieves it as a result. In hyperthyroidism, an inhibitory drug is used for the thyroid gland so that the thyroxine levels in the blood normalize. After surgery or removal of the thyroid gland, as well as in cases of Hashimoto’s thyroiditis, lifelong drug treatment with thyroxine is usually required.
