Thyroid hormones

The thyroid gland has the task of producing hormones from various amino acids (protein building blocks) and the trace element iodine. These have a variety of effects on the body and are particularly necessary for a normal course of growth, development and metabolism. Thyroid hormones have an influence on almost all cells of the body and ensure, for example, an increase in heart strength, normal bone metabolism for a stable skeleton and sufficient heat production to maintain body temperature.

In children, thyroid hormones are particularly important because they are needed for the development of the nervous system and body growth. If a child is born without a thyroid gland and is not treated with thyroid hormones, serious and irreversible mental and physical disabilities and deafness will result. Of the two hormone forms produced by the thyroid gland, T3 (triiodothyronine) is the most effective.

It is produced from the other and mainly produced thyroid hormone T4 (tetraiodothyronine or also thyroxine) by the splitting off of an iodine atom. This conversion is done by enzymes that the body produces in the tissues where the thyroid hormones are needed.A high concentration of enzyme thus ensures a conversion of the less effective T4 into the more active form T3. Tetraiodothyronine (T4), which is usually referred to as thyroxine, is the most produced hormone form of the thyroid gland.

It is very stable and can therefore be easily transported in the blood. However, it is much less effective than T3 (tetraiodothyronine). It is converted into this by splitting off an iodine atom through special enzymes.

If thyroid hormones have to be replaced, for example, due to hypofunction, thyroxine or T4 preparations are usually given, as these do not break down as quickly in the blood and can be activated according to the needs of individual tissues. Thyroxine can also act directly on the cells, just like the other thyroid hormone (T3). However, the effect is significantly less.

Calcitonin is produced by cells in the thyroid gland (so-called C-cells), but it is not a thyroid hormone in the true sense of the word. It differs from the thyroid hormones in its function. In contrast to T3 and T4 with their manifold effects on all possible body functions, Calcitonin is only responsible for the calcium metabolism.

It is released at high calcium levels and ensures that these levels are lowered. The hormone achieves this, for example, by inhibiting the activity of the cells that release calcium through the breakdown of bone substance. In the kidneys, Calcitonin also ensures increased excretion of calcium.

In the intestine it inhibits the absorption of the trace element from food into the blood. Calcitonin has an antagonist with opposite functions that lead to an increase in the calcium level. It is the parathyroid hormone produced by the parathyroid glands.

Together with vitamin D, the two hormones regulate the calcium level. A constant calcium level is very important for many body functions such as muscle activity. Calcitonin plays a further role in very special cases in the diagnosis of thyroid diseases. In a certain form of thyroid cancer, the calcitonin level is extremely elevated and the hormone can serve as a tumor marker. If the thyroid gland of a patient with thyroid cancer has been removed by surgery and a follow-up examination reveals greatly increased Calcitonin levels, this is an indication of cancer cells still remaining in the body.