Thyroid hormones: mechanism of action and physiological effects - Violations

Disorders associated with thyroid hormone

The word "hormone" comes from the Greek hormon - encourage or initiate. This substance was given this name because they play a key role in the response "fight or flight" in sexual desire, in the event of famine and other base motives. Hormones in the body act as ambassadors, heads of regulatory and metabolic processes.

Thyroid hormones, and thyroid hormones, produced in all chordates. The most important element of their structure is iodine - substances which are very much in the sea and on the ground a little. Lack of iodine can lead to hypothyroidism - insufficient production of thyroid hormones. This violation is particularly common in developing countries, where traditional food is not enough iodine, and local residents are not able to take food supplements Food additives - basic classification Containing iodine.

The thyroid gland produces thyroid hormones in response to thyroid-stimulating hormone, which is secreted by the pituitary gland.

There are two main forms of thyroid hormones. Thyroxine (T4) molecule in which four iodine atoms - is an inactive form that can be transformed into T3. Thyroxine is produced only by the thyroid gland. Triiodothyronine (T3) - a molecule with three atoms of iodine, eight times more effective thyroxine Thyroxine - the main thyroid hormone . T4 can be converted to T3 in the thyroid gland, brain, liver and blood flow, as well as in different tissues.

The role of thyroid hormones in the body

One of the most important functions of the thyroid hormone is to convert food into energy and heat. T3 directly stimulates the mitochondria. It stimulates the rapid synthesis of proteins and affects the transcription of mitochondrial genes. This results in cleavage of protein increases the amount of free fatty acids and increases the consumption of oxygen. Thyroid hormones also increase the heart rate, to meet the increased oxygen demand.

In addition, the thyroid hormones regulate the body temperature. Thyroid-stimulating hormone (TSH), which causes the production of these hormones stimulates brown fat tissue to produce heat in the absence of muscle activity (this function is used in infants, as well as in hibernating animals). Thyroid hormone levels vary depending on your calorie intake and ambient temperature. During periods of fasting the body naturally reduces the level of thyroid hormones - it is necessary to reduce calorie needs and prevent the accumulation of ketone bodies in the blood and kidneys. The accumulation of ketone bodies, which occurs, for example, diabetes can result in kidney damage and other parts of the body.

During and after illness injury thyroid hormone levels are also reduced, and restored when the patient recovers.

Thyroid hormones are sensitive to the levels of other hormones, in addition to TSH. Estrogen is partly reduces the effectiveness of thyroid hormones, so the female body to produce them more than men. Perhaps this is the reason that the size of the thyroid gland in women Thyroid cancer in women - the value for the reproductive system   more than men, and that women are more susceptible to various diseases associated with the thyroid gland.

Women who take drugs with thyroid hormone in the framework of hormone replacement therapy, it is necessary to increase the dose, if they plan to start taking hormonal contraceptives. This will prevent the reduction of thyroid hormone under the influence of estrogen Estrogen - the key to bone health . Growth hormone also partially blocks the activity of thyroid hormones, but it also adds to their function in the growth, development and metabolism.

Thyroid hormones play a crucial role in the development of all vertebrates. They bind to receptors of thyroid hormones, which in turn binds to DNA as a result of this is stimulated or inhibited gene transcription.

There are two main forms of thyroid hormone receptor: TRa and TRb. TRa - this nuclear receptor as a receptor and vitamin A and vitamin D, and steroid hormones. Receptors configuration changes when they are attached to T3, and thus they can be combined with specific regions of DNA. Nuclear receptors are often dimerized (associated with other nuclear receptors of the same type or another), but they remain inactive until contact with your triggers. For example, thyroid hormone receptors associated with retinoid X receptors, are not activated until contact with T3 or retinoids (derivatives of vitamin A).

Most of the chemicals that cause hypothyroidism, do not block the thyroid hormone receptor genes; They only reduce the effectiveness of, or interfere with the synthesis of these hormones.

Scientists still do not know all the genes that are regulated by thyroid hormone. It is assumed that under the control of different species of thyroid hormones may be different genes. This is evidenced, for example, that in most mammals hypothyroidism causes similar symptoms (fatigue, tiredness, and so on) and in dogs with this disorder associated additional symptom - cramping. Obviously, canine thyroid hormones affect certain genes, which in humans, they have no direct action.

Genetic disorders associated with thyroid hormone, TSH and thyroid hormone receptors

Resistance to thyroid hormones - is a genetic disorder caused by a mutation of the gene TRb. Patients with the disease has a high level of thyroid hormones and TSH. The consequences of this disorder are less serious than those of congenital hypothyroidism; the most common of them - a slight increase, slow bone development, hyperactivity, learning disabilities, hearing problems, and mixed symptoms characteristic of hypothyroidism and hyperthyroidism.

Pendred syndrome is caused by a genetic defect that limits the possibility of the inclusion of iodine in the thyroid hormones, which is why the structure of the hormones is disrupted. Often the consequences are Pendred syndrome, hypothyroidism and goiter. The body of the patient tries to compensate for the lack of full of hormones, spending more energy to produce thyroid hormones. In some cases, the syndrome causes complete deafness - usually it is present from birth. If a patient with hypothyroidism Pendred syndrome develops in older age, it can cause symptoms such as hearing loss and tinnitus, but it is, as opposed to total deafness, it is treatable.

TSH receptor gene mutation can cause hyperthyroidism or insensitivity to TSH. Typically, patients with the normal levels of thyroid hormones and increased TSH levels. Impact of TSH cells and brain cells is not completely understood, but it is known that changes in the level of TSH affects the brain and the immune system.

Thyroid hormones play an important role in brain development from mid-pregnancy to the end of the second year of life. Hypothyroidism is the mother or the fetus, caused by iodine deficiency during pregnancy, or other causes, may lead to cretinism. With timely treatment, which should start in the first months of life, a child's intelligence may be normal; otherwise the child will be seriously behind in mental development, and this state is not subject to a substantial correction. TRa gene mutations may also cause severe and incurable form of cretinism.