Thyroxine and triiodothyronine are synthesized on the basis of what? Thyroid hormones - thyroxine and triiodothyronine

Thyroid hormones are produced in the thyroid gland (SCH). Thyroxine and triiodothyronine are the two main hormones of this organ, which contain an iodine atom. These hormones are produced by cells of the follicular epithelium.

The role of thyroid hormones

Thyroxine and triiodothyronine are synthesized on the basis of tyrosine (alpha-amino acid) and are of great importance for the normal development of the whole organism.

• Support the work of the respiratory center.
• With their participation, the formation of heat by the body is monitored.
• They affect oxygen exchange and increase the need for tissues in oxygen.
• Affect the force of the heartbeats (ionotropic effect).
• Regulate the frequency of heart contractions (chronotropic effect).
• Due to thyroid hormones, the number of β-adrenergic receptors in skeletal and cardiac muscles, as well as located in adipose tissue and lymphocytes, increases.
• Activate the motility of the entire gastrointestinal tract.
• Under their influence, various structural proteins are synthesized and tissue differentiation occurs.
• Stimulate the development and growth of the whole body.
• Stimulate the work of the central nervous system and accelerate thought associations.
• Regulate glucose in the blood and increase the capture and utilization of its cells, thereby activating the process of glycolysis.
• Affect the breakdown of fatty tissue (lipolysis) and delay its formation and deposition.

Violation of the secretion of thyroid hormones in the human body can lead to a delay in mental and physical development.

Synthesis of hormones SHCHZ

The main protein is a thyroglobulin. It serves as a matrix for the formation of hormones produced by the gland. Thyroxine and triiodothyronine are synthesized on the basis of thyroglobulin protein. This protein contains more than 5 thousand amino acid residues and only 18 of them are iodinated. Thyroxine is synthesized with the participation of only 2 to 4 amino acid residues. In addition to thyroglobulin, cholesterol also participates in the production of thyroid hormones. Thus, thyroxine and triiodothyronine are synthesized on the basis of cholesterol, like steroid hormones. The thyroid hormone T4 is produced 10 times more than T3.

Triiodothyronine hormone (T3) is formed as a result of the combination of the molecules of di- and monoiodotyrosine, which are part of the thyroglobulin protein.

How do hormones SHCHZ come to the tissues?

Hormones SHCHZ bind to blood plasma proteins and in this form are delivered to tissues and organs. There are three main blood proteins that are able to bind the hormones T3 and T4:

1. TSH - thyroxine-binding globulin.
2. TSPA is a thyroxine-binding prealbumin.
3. Albumen.

The level of thyroxin and triiodothyronine is affected by the secretory activity of the thyroid gland and the binding capacity of blood serum.

The synthesis of T3 and T4 is controlled by the hormone pituitary TSH (thyreotropic hormone). In turn, the synthesis of TSH is carried out under the influence of the hormone hypothalamus TRH (thyrotropin-releasing hormone).

Triiodothyronine free (fT3)

The percentage of fT3 is only 0.25% of the total T3 in the blood. As we have already seen, T3 in the blood is much less than T4, but despite this, its free form is only half the size of the free form of T4.

It is the free form of hormones SHCHZ causes their biological activity. Triiodothyronine (a hormone) is much more active than a thyroxine. That is why its free level characterizes the general metabolic action of thyroid hormones.

Thyroxine: Functions

T4 is biologically inactive. But, if necessary, it can be transformed into a more active T3 under the influence of the enzyme selenium-dependent monodeiodinase.

The hormone thyroxine functions in the body performs as important as triiodothyronine. Namely, T4 is responsible for the production of vitamin A in the liver, stimulates protein metabolism, affects lipid (fat) metabolism, regulates the level of triglycerides and bad cholesterol in the blood, influences the correct formation of bone tissue, which is especially important in childhood.

How correctly to hand over the analysis on hormones SHCHZ?

In order to make a study of the level of hormones SHCHZ, it is enough to pass on the blood from the vein. This can be done in the treatment room.

For the study to be performed most reliably and its results were not affected by external factors, one month prior to blood donation for analysis, it is necessary to exclude the intake of all hormonal preparations. Of course, this should be agreed with the attending physician. 3-5 days before delivery, it is recommended to exclude drugs containing iodine.

Immediately before taking blood, the patient should not undergo any radiographic examination. On the eve of blood donation, high physical activity and stressful situations (sports competitions, passing exams, etc.) are not recommended. Before entering the room and taking the test, the patient is recommended to sit and rest for 15-30 minutes.

Normal values of hormones SHCHZ

We found out what role in the body is played by thyroxin and triiodothyronine, synthesized on the basis of which components, what substances are responsible for their binding in the blood serum, how correctly to pass an analysis for these hormones. Now consider their normal values and under what diseases they can increase or decrease. The norms of these hormones are given in the table below:

At what diseases does fT3 increase?

Triiodothyronine free can increase with the following diseases:

• Hyperthyroidism is primary or secondary.
• T3 toxicosis isolated.
• Thyroiditis.
• Hypothyroidism is T4-resistant.
• Choriocarcinoma.
• Syndrome of resistance to hormones SHCHZ.
• Decrease in the concentration of thyroxine-binding globulin.
• Chronic liver diseases.
• When hemodialysis.
• With nephrotic syndrome.
• After therapy with preparations of radioactive iodine.

In what cases is the decrease in fT3?

A decrease in fT3 in the blood can occur in the following situations:

• Hypothyroidism is primary, secondary or tertiary.
• Non-thyroid pathology of severe form, including mental and somatic diseases (stroke, heart attack, etc.).
• Long-term fasting or a diet with low intake of protein.
• During recovery from severe pathologies and surgeries.
• With primary uncompensated adrenal insufficiency.
• In women with regular heavy physical exertion.
• In the third trimester of pregnancy (the level of fT3 during pregnancy is steadily declining since the first trimester and by the end of the third it becomes most pronounced).
• When taking the following medicines: amiodarone, androgens, propranolol, salicylates, radiopaque iodine-containing drugs.

In addition, seasonal fluctuations of fT3 are possible. The maximum falls on the time interval from September to February, and at least for the summer months.

Symptoms of hypothyroidism

Hypothyroidism is an inadequate synthesis of the hormones SHCHZ. In this case, the following symptoms may occur:

• Lethargy, fast fatigue and drowsiness.
• The appearance of excess weight, which can not be regulated due to exercise and diets.
• Constant depression.
• There may be a decrease in body temperature to 35.6 degrees.
• Itching of the skin, their dryness and swelling.
• Hair loss and dandruff, which does not pass even after the use of therapeutic shampoos.
• Reduction of heart rate (bradycardia).
• Low blood pressure.
• Decreased memory and reaction.
• Regular constipation.
• Women can provoke a menstrual cycle and infertility.

Symptoms of hyperthyroidism

Hyperthyroidism is an excess of synthesis of the hormones SHCHZ. The following symptomatology is observed:

• Increased appetite and weight loss.
• General weakness, on the background of which an outburst of excitement can be observed.
• Laxity and dry skin.
• Heart palpitations and increased blood pressure.
• Raise the body temperature to 37.5 degrees.
• Violation of the menstrual cycle in women and infertility.
• In severe cases, a marked increase in thyroid gland and bladder eyes.

Prophylaxis of diseases SCHZ

The thyroid gland and its hormones perform the most important functions for the body, therefore it is necessary to monitor the condition of this organ. This is done on annual preventive examinations. If necessary, the doctor will give directions to ultrasound and analysis of hormones SHCHZ.

To prevent diseases of the thyroid gland and the lack of hormones of this body, it is necessary to include foods with a high iodine content in your diet. They include almost all seafood (tuna, flounder, salmon, shrimp, sea kale), fruits (persimmon, bananas, oranges), vegetables (onions, garlic, sorrel, eggplant). Observing simple recommendations, you can permanently maintain the health of the thyroid gland and the entire body as a whole.