The thyroid gland (thyroid gland) consists of 2 lobes and a narrow isthmus connecting them. It has the appearance of a butterfly, located on the front of the neck under the larynx, covered by cartilage. The size of the gland is 3-4 cm, and it weighs only about 20 g.
A bit of anatomy
The thyroid determines the work of the entire endocrine system. But it is unique not only by this. The thyroid gland is the only organ that produces hormones and stores them in its reserve before they enter the bloodstream. The secret produced is secreted into the circulatory system only when necessary.
The parenchyma consists of follicular vesicles that have only 1 epithelial layer (thyrocytes). The unusual thing is that at rest, the epithelium is flat and does not produce a secret. With depletion of reserves, the layer takes a cubic form and synthesizes the necessary amount of hormones. They are stored in the form of thyroglobulin in the follicles until their release from the pituitary gland under the influence of TSH.
Inside the follicles contain a colloid. This is a viscous liquid in which thyroglobulin protein is stored. Thyroid hormone is called thyroxine, and thyroglobulin is its precursor.
Work rate
Providing the body with energy, the thyroid gland itself is controlled by another endocrine gland - the pituitary gland. He himself depends on the hypothalamus. The pituitary hormone that regulates the activity of the thyroid gland is called thyrotropin or TSH. Its function is to stimulate triiodothyronine (T3) and thyroxine (T4).
Thyroid hormones contain iodine atoms, that is, they are iodized. Deficiency of this substance always leads to malfunction of the gland. Accordingly, iodinated hormones are called iodothyronines or thyroids. The thyroid gland produces several of their types, each of which has its own functions: T4, T3, thyroglobulin, calcitonin. The numbers indicate the number of iodine atoms.
T4 - thyroxine - is biologically inactive, produced in the largest quantity - 92%. The active and main hormone is T3, which is produced from T4 by cleaving 1 iodine atom from it. The reaction occurs when the TPO enzyme, thyroperoxidase, interacts. T3 is 10 times more active than the hormone T4.
The functions of thyroid hormones
Thyroid hormones have the following functions:
- Thyroid accelerates metabolism;
- regulate the growth and development of the fetus;
- in women affect reproductive function;
- with its lack, infertility can develop;
- take part in the synthesis of vitamin A;
- regulate the work of enzymes;
- responsible for the condition of the skin and hair, skeletal system and physical development;
- activate the brain and vascular system.
Another thyroid hormone called calcitonin will be described below.
Work and hormone formation
Free hormones make up only 1%, but they determine all the work of the thyroid gland, and related ones do not function.
Some thyroid hormones are called the thyroid. These are derivatives of alpha amino acids (tyrosine). The main functions of the hormone are as follows:
- he is involved in tissue growth;
- increases oxygen uptake by tissues;
- contribute to the synthesis of red blood cells by affecting the bone marrow;
- participates in water metabolism;
- affects blood pressure, stabilizing it, if necessary, increases the strength of heart contractions (with an excess of T3, heart rate immediately increases by 20%);
- accelerates thought processes and motor-mental activity;
- responsible for metabolic processes;
- participates in thermoregulation;
- increases immunity and removes bad cholesterol;
- increases glucose levels and affects gluconeogenesis in the liver, and this inhibits glycogen synthesis.
Participation in metabolism is expressed in accelerating lipolysis, maintaining harmony and normal weight. Hormones act as anabolic steroids on protein synthesis and maintain a positive (normal) nitrogen metabolism. When there is an overabundance in their action, they resemble catabolics, and the nitrogen balance is disturbed.
T3 functions
Triiodothyronine free or T3 free - the so-called thyroid hormone. He is the most active of all. The two main thyroid hormones (T3 and T4) are inextricably linked, as one is formed from the other. Triiodothyronine remains the main one, although it is produced in small quantities. As mentioned earlier, the main hormone secreted by the thyroid gland is called thyroxine. He is the precursor of T3 and becomes the "engine" for the work of the whole organism:
- enhances the transport of amino acids;
- allows you to digest vitamins, proteins, carbohydrates;
- helps in the synthesis of vitamin A.
What is the name of the thyroid hormone in gynecology? Free FT3 and FT4 are often referred to as “female” because reproductive function in all its manifestations depends on them. When it enters the bloodstream, T3 binds to transporter proteins, which deliver it to the place of necessary presence.
Norm T3
All hormones are dependent on the time of year, day, age and gender. The highest T3 is observed in the fall-winter, and the lowest - in the summer. Its level depending on age:
- from 1 to 19 years - up to 3.23 nmol / l;
- from 20 years - up to 3.14 nmol / l;
- at the age of 50 years - up to 2.79 nmol / l.
Thyroxine
In a biological sense, it is inactive, but indispensable for humans. T4 is produced in the follicles. It is noteworthy that thyroxine (the so-called main thyroid hormone) is produced only with the participation of thyrotropin.
FT4 and T4 are one hormone that circulates in the blood in different ways. It should be noted that the amount of T3 always depends on T4.
Norm T4
Norm T4 St. (free) in women, it ranges from 71.23 to 142.25 nmol / L; in men - from 60.77 to 136.89 nmol / l. Such large intervals depend on age. The highest level of T4 is noted from 8 a.m. to 12 p.m. at this time it is best to take tests. From 23 hours its content drops, and the lowest level is observed at 3 o’clock in the morning. Fluctuations can be caused by various diseases. In what cases T4 St. and T3 can be increased? This happens when:
- myeloma;
- obesity;
- kidney disease;
- thyroid disorders after childbirth;
- thyroiditis;
- HIV
- diffuse goiter;
- porphyria;
- liver pathology;
- after hemodialysis.
It is also possible when taking analogues of thyroxine, methadone, prostaglandins, Cordarone, Tamoxifen, radiopaque iodine-containing substances, Insulin and Levodopa.
A decrease in hormone levels was noted with:
- low protein diet;
- hypothyroidism;
- sheehan syndrome;
- injuries
- endemic goiter;
- inflammation in the higher links of the endocrine system - the pituitary gland and hypothalamus;
- after illness;
- adrenal gland disorders.
Taking certain drugs also gives a decrease in thyroid hormones. Among them it is worth noting:
- Tamoxifen;
- "Merkazolil";
- beta blockers;
- statins
- steroids;
- anabolics;
- diuretics;
- "Propylthiouracil";
- muscle relaxants;
- radiopaque preparations.
What to do when increasing T3?
Firstly, do not forget about the possibility of errors in research. This becomes possible if the rules for the analysis are not followed. Secondly, you should immediately consult an endocrinologist.
Thyroid-stimulating hormone (TSH, TSH)
Thyrotropin is an adenohypophysis hormone. It plays a major role in the smooth operation of the thyroid gland. The relationship between thyroids and TSH is the opposite. The international TSH norm is considered to be a range from 0.4 to 4.0 μMU / ml.
Hormone thyrocalcitonin
Another hormone produced by the thyroid gland is called calcitonin or thyrocalcitonin. It is produced by parafollicular gland cells. It is important for calcium-phosphorus metabolism and is an antagonist of parathyroid hormone.
Calcitonin reduces the level of P and Ca in the blood, and also stimulates the development and functioning of osteoblasts (bone cells). This is a tumor marker for checking thyroid cancer. If its amount exceeds 100 pg / ml, then the likelihood of cancer.
Calcitonin is also an indicator of the effectiveness of cancer therapy. The analysis for this hormone is constantly given to those to whom the thyroid gland was removed in order to diagnose a tumor relapse in time.
Diseases in which calcitonin levels increase:
- pancreatitis
- liver cancer;
- the stomach;
- liver failure;
- thyroiditis;
- pernicious anemia.
Norm calcitonin
Its norm depends on the gender of the person. With the ELISA method, calcitonin in men should be 0.68-32.26 mg / ml. For women, the norm is: 0.07-12.97 pg / ml.
Indications for analyzes on thyroid hormones
Analyzes will be needed in the following cases:
- identification of signs of thyrotoxicosis (tachycardia, weight loss, tremor of the body and hands, tearfulness, nervousness, increased appetite, effervescence, extrasystole, etc.);
- signs of hypothyroidism (bradycardia, weight gain, slowing of thinking and speech, dry skin, decreased libido);
- visual and ultrasound enlargement of the gland;
- the presence of nodes in it;
- infertility;
- menstrual irregularities (amenorrhea);
- miscarriage;
- heart rhythm disturbances;
- lipid metabolism disorders with increased blood cholesterol;
- anemia;
- decreased sexual activity;
- galactorrhea;
- developmental delay of the child;
- to control treatment for pathologies of the gland;
- control after thyroid surgery;
- analysis for TSH is included in the neonatal screening, that is, is mandatory for all newborns in Russia;
- baldness (alopecia);
- obesity.
What thyroid hormones need to be taken
What are thyroid hormone tests called? Everything is very simple: this is hormonal research. The analysis is always carried out comprehensively. That is, T3, T4 and TTG are necessarily determined.
TTG is an indicator of normal thyroid function. He is "the head of the family", and his blood level is determined for any pathology of the gland. The definition of TSH is called a hormonal status study.
T3 St. - is responsible for the oxygen metabolism of cells and tissues. The determination of concentration is a complex study, so mistakes are often made here.
T4 St. - is responsible for protein synthesis and its stimulation. In a blood test, the doctor can also prescribe the definition of AT-TG - antibodies to thyroglobulin and AT-IPO - antibodies to typereoid peroxidase. These tests can detect autoimmune diseases and are important in differential diagnosis. The norm of AT-TG is from 0 to 4.11 IU / l.
AT-TPO is the most sensitive test for detecting autoimmune processes in the gland. It is a definition of antibodies to a cellular enzyme. The norm of AT-TPO is from 0 to 20 IU / l. Some laboratories consider 120 IU / L to be the norm, so the values of the norm should be on the forms.
Decryption of analyzes
Decryption should be carried out only by an endocrinologist, not even a laboratory assistant.
- With an increase in TSH, one can think of hypothyroidism in a patient, but T4 and T3 are of decisive importance.
- With increased TSH and decreased T4 - obvious manifest hypothyroidism. If T4 is normal against the background of elevated TSH, this is subclinical hypothyroidism.
- With normal TSH, but reduced T4 in 99% of cases, the result is a laboratory error. Necessarily need a new retake of biomaterial for analysis. Also, the TSH norm and reduced T3 will be an error.
- A decrease in TSH indicates an excess activity of the organ - hyperthyroidism. In this case, T3 and T4 (thyroid hormones) are increased. If they are within normal limits against a decrease in TSH, this is subclinical hyperthyroidism.
Hormone rate
Why can the performance of different laboratories vary? Because everywhere there are their own equipment features, different models of research apparatuses, the difference in their settings, and the reagents used.
The basis of the values are, of course, international standards, but each laboratory makes its own adjustments. The difference is small, but this can lead to false diagnoses. Therefore, reference values should be indicated on laboratory blanks.
Blood for thyroid hormones: what’s called
What thyroid hormones are called, and what functions they perform, we figured out. Now it is important to dwell on the rules for passing tests. They are not complicated, but their knowledge and implementation will help to get true results. Some are cumbersome in a series of prohibitions, which upon closer examination are somewhat exaggerated. It is not necessary to limit oneself in nutrition. The fact is that on thyroid hormones the food taken is not reflected - they are so stable that the analysis can be taken at any time of the day or even immediately after a meal. But this is only if there is no need to donate blood for other studies.
During the day, the level of TSH changes slightly. Often there are recommendations that when treating with hormonal agents, their intake should be stopped a month before the study. This is an unfounded statement. Such a measure would only do harm.
You can also find recommendations for stopping iodine-containing drugs a week before delivery. However, they also do not affect performance.
Women need to remember: the level of thyroid hormones does not depend on the cycle, so you can donate blood at any convenient day. Menstruation only affects sex hormones.
But here is the important thing! Before taking blood for analysis, you can not take an x-ray, ECG, ultrasound or physiotherapy. All these studies should be carried out 2-4 days before the procedure.