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


2018-04-01 16:18:20




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Thyroid hormones are produced in the thyroid gland (now the thyroid gland). Thyroxine and triiodothyronine are the two main hormone that body, which consists of an atom of iodine. These hormones are secreted by the cells of the follicular epithelium.

Thyroxine and triiodothyronine are synthesized based on

The Role of thyroid hormones

Thyroxine and triiodothyronine are synthesized based on tyrosine (alpha-amino acid) and essential for the normal development of the organism.

  • Support the work of the respiratory center.
  • With their participation, the education of body heat.
  • Affect oxygen metabolism and increase the need tissues of oxygen.
  • Affect the force of cardiac contraction (ionotropic effect).
  • Regulate the heart rate (chronotropic effect).
  • Due to the thyroid hormone increases the number of b-adrenergic receptors in skeletal and cardiac muscle as well as adipose tissue and lymphocytes.
  • Activate the motility of the entire gastrointestinal tract.
  • Under their influence the synthesis of structural proteins and differentiation of tissues.
  • Encourage the development and growth of the whole organism.
  • Stimulate the CNS and accelerate the thinking of the Association.
  • Regulate glucose in the blood and increase the capture and utilization of her cells, thereby activating the process of glycolysis.
  • Affect the breakup of adipose tissue (lipolysis) and inhibits its formation and deposition.

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

Thyroxine: function

Synthesis of hormones now the thyroid gland

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


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Triiodothyronine hormone (T3) is formed by connecting molecules of di - and monoiodotyrosine, which are part of the protein thyroglobulin.

How do hormones now the thyroid gland to the tissues?

Now the thyroid gland Hormones bind to plasma proteins and in this form are delivered to tissues and organs. There are three main blood protein that can bind the hormone T3 and T4

  1. TSG - thyroxine binding globulin.
  2. TSPA - thyroxine binding prealbumin.
  3. Albumin.

free Triiodothyronine

The level of thyroxine and triiodothyronine affect the secretory activity now the thyroid gland and the binding capacity of blood serum.

Control of the synthesis of T3 and T4 is pituitary hormone TSH (thyroid stimulating hormone). In turn, the synthesis of TSH is 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 content of T3 in the blood. As we have seen, T3 in the blood is much smaller than T4, but in spite of this, the free form is just two times less than the free form of T4.

It is a free form of hormones now the thyroid gland determines their biological activity. Triiodothyronine (hormone) is much more active than thyroxine. That is why free level it describes the overall metabolic effect of thyroid hormones.

Thyroxine functions

T4 is biologically inactive. But if necessary it may be under the influence of the enzyme selenium-dependent monodeiodination be converted into the more active T3.

Triiodothyronine hormone

Hormone thyroxine function in the body performs such as important as triiodothyronine. Namely, T4 is responsible for the production in the liver of vitamin A, stimulates protein metabolic processes, affect lipid (fat) metabolism, regulates the level of triglycerides and bad cholesterol in the blood, affects the proper formation of bone tissue, especially in children.

How to get tested for hormones now the thyroid gland?

To produce a study of the level of hormones now the thyroid gland, it is enough to take on the analysis blood from a vein. This can be done in the treatment room.

The study was undertaken the most reliable and its results are not affected by external factors, one month before delivery of blood it is necessary to exclude reception of all hormones. Of course, this must be agreed with your doctor. 3-5 days before delivery it is recommended that medicines containing iodine.

Immediately before blood sampling, the patient should not undergo any x-ray examination. On the eve of blood donation is not recommended high physical activity and stressful situations (sporting events, exams, etc.). Before you go to the office and take the test, the patient is advised to sit and relax for 15-30 minutes.

Thyroxine and diyodtirosin

Normal values of hormonesNow the thyroid gland

We figured out what role to play in the body thyroxine and triiodothyronine, synthesized on the basis of what components, what substances are responsible for their binding in blood serum, how to get tested for these hormones. Now consider their normal value and under what conditions they can increase or decrease. The norms of these hormones are given in the table below:

HormoneMinimum and maximum valuesUnits izmereniya
At-TG (antibodies to thyroglobulin)0-18,0U/ml
TG (thyroglobulin)1,6-5,9Ng/ml
Antibodies to thyroid peroxidase<5,6U/ml

In what diseases increased fT3?

Free Triiodothyronine may increase in the following conditions:

  • Hyperthyroidism primary or secondary.
  • Isolated T3 toxicosis.
  • Others.
  • Hypothyroidism T4-resistant.
  • Choriocarcinoma.
  • The Syndrome of resistance to now the thyroid gland hormones.
  • Reduction of the concentration of thyroxine binding globulin.
  • Chronic liver disease.
  • During hemodialysis.
  • Nephrotic syndrome
  • After therapy, radioactive iodine preparations.

In some cases there is a decrease in fT3?

The Decrease in fT3 in the blood can occur in the following situations:

  • Hypothyroidism primary, secondary, or tertiary.
  • Netrevenue pathology is severe, including mental and physical illness (stroke, heart attack, etc.).
  • Prolonged fasting or a diet low eating protein.
  • The recovery period after serious illnesses and operations.
  • Non-compensated primary adrenal failure.
  • In women with regular heavy physical exertion.
  • In the third trimester of pregnancy (level of fT3 in pregnancy has been steadily declining since the first trimester and by the end of the third becomes most pronounced).
  • When taking the following drugs: amiodarone, androgens, propranolol, salicylates, radiopaque yodsoderzhaschie funds.

In addition, possible seasonal fluctuations fT3. The maximum is in the time period from September to February and a minimum in summer months.

Thyroxine is synthesized

Hypothyroidism Symptoms

Hypothyroidism is the insufficient synthesis of hormones now the thyroid gland. In this scenario, you may experience the following symptoms:

  • Lethargy, fatigue and drowsiness.
  • The Emergence of excess weight, which cannot be controlled by exercise and diet.
  • Constant depression.
  • You May experience a decrease in body temperature to 35.6 degrees.
  • Itching of the skin, their dryness and puffiness.
  • Hair Loss and dandruff that does not go away even after using treatment shampoos.
  • Reduced heart rate (bradycardia).
  • Low blood pressure.
  • Loss of memory and reaction.
  • Regular constipation.
  • In women can cause menstrual disorders and infertility.

Symptoms of hyperthyroidism

Hyperthyroidism is an excess of hormone synthesis now the thyroid gland. You experience the following symptoms:

  • Increased appetite and weight loss.
  • Weakness, which may be a flash excitation.
  • Sagging and dry skin.
  • Rapid heartbeat and increased blood pressure.
  • Increased body temperature to 37.5 degrees.
  • Disruption of the menstrual cycle in women and infertility.
  • In severe cases, a noticeable increase now the thyroid gland and exophthalmia.

Disease Prevention now the thyroid gland

The Thyroid gland and its hormones perform important functions for the body, it is therefore necessary to monitor the status of this body. This is done on an annual prophylactic examinations. If necessary, the doctor will give direction to the ultrasound and blood hormones now the thyroid gland.

Level thyroxine

To prevent diseases now the thyroid gland and hormonal deficiency of this body should include in your diet foods high in iodine content. These include virtually all seafood (tuna, flounder, salmon, shrimp, sea cabbage), fruit (persimmons, bananas, oranges), vegetables (onion, garlic, sorrel, eggplant). Following the simple guidelines, it is possible to preserve the health of the thyroid gland and the whole body.

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