The thyroid gland is the largest organ of the endocrine system. It is located on the neck on both sides of the upper trachea and looks like a butterfly. Thyroid follicles normally synthesize the hormones triiodothyronine (T3) and tetraiodothyronine (T4 or thyroxine). Since the thyroid gland in Latin sounds like "thyroid gland", the hormones that it synthesizes are called thyroid hormones. They bind to protein to form thyroglobulin, and in this form can be stored in the follicles of the gland for several months. As needed, thyroglobulin breaks down, hormones are released. Then they enter the circulatory system and are distributed throughout the body by special carrier proteins, and then penetrate into the tissues of our body.
Water, mill and thyroid hormones
They say that the thyroid gland "pours water on the mill of our lives." This ismeans that normally thyroid hormones provide a person with activity, good mood, and children - growth and development. If the thyroid gland does not work well - “pouring little water”, then “the mill turns slowly”, that is, the person becomes inhibited, apathetic, and children do not grow, their mental development is delayed. How can this be scientifically explained?
The primary biochemical effect of thyroid hormones is the activation of protein synthesis. Thyroid hormones normally penetrate into cells, interact with cell DNA, changing the activity of certain parts of the genome. As a result, the synthesis of mainly enzyme proteins and receptor proteins is enhanced. Both those and others regulate metabolism in general.
The norm of indicators of the thyroid gland
Usually, blood is taken to study the level of thyroid hormones if a disease of this gland is suspected.
Normal levels of hormones and other indicators of the thyroid gland are shown in Table 1.
| Table 1. Norm of thyroid hormones in women | ||
| TTG | µIU/ml | 0, 4-4, 0 |
| T3 gen | nmol/L | 1, 2-2, 7 |
| T3 sv | pmol/L | 2, 3-6, 4 |
| T4 gen | nmol/L | 55-156 |
| T4 s | pmol/L | 10, 3-24, 6 |
| Thyroglobulin | ng/ml | ≦56 |
| Thyroxine binding globulin | nmol/L | 259-575, 6 |
| Antibodies to tereoglobulin | µIU/ml | ≦65 |
| Anti-thyroid peroxidase antibodies | ≦35 | |
| Antibodies to TSH receptor | IU/L | ≦1, 8 negative |
| ≧2, 0 positive | ||
Thyroglobulin, antibodies to thyroglobulin
The production of thyroid hormones occurs in the cells of the thyroid gland - thyrocytes. For the synthesis of hormones, the amino acid tyrosine and the trace element iodine are needed. Tyrosine is part of the thyroglobulin molecule. Two iodine atoms and a phenol group are attached to tyrosine. The resulting compound is called thyronin. One more iodine can join it with the formation of triiodothyronine, or the hormone T3, and one more iodine can be added to it with the formation of tetraiodothyronine (tetra means 4), or the hormone T4, also called thyroxine.
The resulting hormones are stored in the cells of the gland as part of thyroglobulin. As necessary, the complex of hormones and thyroglobulin is destroyed, hormones enter the bloodstream to perform their function. Together with them, a small amount of iodine and thyroglobulin enters the bloodstream. This is important to know for understanding the mechanism of development of autoimmune diseases. Previously, it was believed that thyroglobulin enters the bloodstream only with thyroid pathology, and therefore causes the formation of antibodies to itself. It has now been established that thyroglobulin is normal in the blood.
Anti-thyroid peroxidase antibodies
As already mentioned, thyroid hormones are synthesized from tyrosine and iodine. The source of iodine is food, especially seafood. Iodine supplied with food is inorganic, absorbed in the intestines, enters the bloodstream, from where it is captured by the thyroid gland. In order for such iodine to become active and be able to integrate into organic molecules, it must be oxidized. It is oxidized by hydrogen peroxide with the participation of the enzyme iodide peroxidase, which is also called thyroid peroxidase. Without this enzyme, hormones will not be synthesized, even if iodine enters the body in the right amount.
Free and bound T4 thyroxin-binding globulin
Normally, in women, thyroid hormones T4 in the blood are 99.95% bound. Hormones bind to special carrier proteins. This protects the hormone from destruction and creates its reserve. In 80% of cases, this protein is thyroxin-binding globulin. There is an insignificant amount of thyroxin in the free form in the blood plasma, but it is this free thyroxine that has activity.
Free and bound T3
In the blood, 99.5% of the hormone T3 is in a bound form, 90% of it joins the thyroxin-binding hormone. Of the total amount of T3 in the blood, only 15% is synthesized in the follicles of the thyroid gland, the rest of the hormone is obtained in the liver when one iodine is split off from T4. As can be seen from Table 1, in the bloodT3 is less than T4, but its physiological activity is 4 times higher. In addition, studies have shown that it is T3 that performs a hormonal function in cells (they react with nuclear receptors, thus affecting the DNA of the cell). This confirms the opinion that the true thyroid hormone is normally T3, and T4 is a prohormone.
TTG
Thyroid hormones perform an extremely important function in the body - they regulate the synthesis of proteins in all cells of the body, so their production is controlled at several levels:
- bark of the cerebral hemispheres;
- hypothalamus via efferent nerves;
- hypothalamus via pituitary gland;
- depending on the amount of iodine in the body.
Yet the main way to regulate the synthesis of hormones is the third of those listed. In the hypothalamus, a signal is formed that affects the pituitary gland and stimulates the production of thyroid-stimulating hormone (that is, directed to the thyroid gland) in it - TSH. It activates the synthesis of thyroglobulin in the thyroid gland, which is a precursor of thyroid hormones. When a sufficient amount of these hormones is produced, the formation of TSH is suppressed, thyroid hormones normally cease to be synthesized (feedback). With the help of such complex mechanisms, a fine regulation of the thyroid gland is carried out, adapting to the changing needs of the whole organism.
Change in the content of TSH in the blood - the first call of a malfunctionthyroid glands. If the TSH level in women is normal, then the thyroid hormones will probably be in order too.
Pregnancy and the thyroid gland
The main regulator of thyroid hormone production is TSH. During pregnancy, the placenta produces chorionic gonadotropin, which also activates the production of thyroid hormones. Therefore, in pregnant women, the rate of thyroid hormones in the blood increases. Chorionic gonadotropin begins to be synthesized 6 hours after fertilization, its presence in the blood inhibits the synthesis of TSH. Around the 4th month, the situation returns to normal. Therefore, serum TSH levels fluctuate during pregnancy.
Estrogens also influence the synthesis of thyroid hormones. During pregnancy, there are more of them, and the thyroid gland secretes hormones more actively. Then the mechanism of deactivation of hormones in the blood by thyroxin-binding globulin is activated, its synthesis in the liver increases, which will be reflected in the results of the analysis.
Another factor in the activation of the gland in the second half of pregnancy is a decrease in the content of iodine in the blood due to its diversion to the fetoplacental complex. Iodine, in addition, in pregnant women is intensively excreted in the urine.
All of these factors lead to hyperfunction of the gland. In the blood, an increased level of total T3 and total T4, free T3 and T 4 will be fine.
| Table 2. Norm of thyroid hormones in pregnant women | ||
| TTG | µIU/ml | 0, 2-3, 5 |
| T4 gen | nmol/L |
I trimester 100-209 |
|
II, III trimester 117-236 |
||
| T4 s | pmol/L |
I trimester 10, 3-24, 6 |
|
II, III trimester 8, 2-24, 7 |
||
Interpretation of thyroid test results
To assess the work of the thyroid gland, laboratory (determination of the content of hormones in the blood) and instrumental (ultrasound) studies are used.
The state of the body, in which no signs of abnormalities in the thyroid gland are found, is called euthyroidism. A condition in which there are signs of excessive work of the gland (hyperfunction) is called hyperthyroidism; insufficient work of the gland (hypofunction) - hypothyroidism.
The norm in the analysis of thyroid hormones in women is much less common than in men, since it is women who are prone to various pathologies of the thyroid gland.
| Table 3. Typical changes in blood parameters in thyroid pathologies | |||||
| T3 st | T4 s | TTG | AT-TG | at-TPO | |
| Primary hypothyroidism. | Low or normal | Low or normal | High | ||
| Hypothyroidism secondary. | Low | Low | Low | ||
| Primary hyperthyroidism. | High | High | Low | ||
| Autoimmune thyroiditis. The thyroid gland is inflamed. | Possibly both an increase and a decrease in hormone levels | High | High | ||
Table 4 shows diseases and various conditions of the body, which are characterized by changes in the performance of the thyroid gland.
| Table 4. Diagnosis of various conditions based on blood tests | ||
| Increase | Decrease | |
|
T4 gen |
Thyrotoxic goiter; pregnancy, postpartum thyroid dysfunction; hormone-producing tumors of the thyroid gland, inflammation of the gland; pathology of the liver and kidneys, obesity; medication - thyroid hormones, iodine-containing, estrogen, insulin, oral contraceptives; HIV infection, AIDS. |
Hypothyroidism; medication - antithyroid drugs, iodides, glucocorticoids, non-steroidal anti-inflammatory drugs, anticancer, antituberculosis, hypolipidemic, anticonvulsant, antifungal drugs, lithium s alts, furosemide; significant iodine deficiency in the body. |
|
T4 sv |
Toxic goiter; thyroiditis; postpartum gland dysfunction, nephroticsyndrome, obesity; medication - oral contraceptives, estrogens, thyroid drugs, TSH; prolonged tourniquet for blood sampling. |
Primary hypothyroidism, which manifests itself as: autoimmune thyroiditis, endemic goiter, tumors in the thyroid gland, removal of part or all of the gland; secondary hypothyroidism; tertiary hypothyroidism due to brain injury or inflammation in the hypothalamus; lack of protein and iodine intake; medication - anabolic steroids, anticonvulsants, lithium preparations, oral contraceptives, overdose of thyreostatics; lead exposure, surgery, dramatic weight loss in obese women. |
| T3 gen and sv |
Thyrotoxic goiter; inflammation of the gland, some tumors of the gland, isolated T3-toxicosis, impaired TSH synthesis, resistance to thyroid hormones; postpartum gland dysfunction, kidney and liver pathology, hemodialysis, weight gain; taking drugs - estrogens, levothyroxine, oral contraceptives. |
Hypothyroidism; severe illness, mental illness; insufficient protein intake; taking drugs - antithyroid drugs, glucocorticoids, beta-blockers, nonsteroidal anti-inflammatory drugs, lipid-lowering drugs, oral contraceptives, radiopaque agents. |
| TTG |
Hypothyroidism; pregnancy; hypphoid tumors; immunity to thyroid hormones, juvenile hypothyroidism, decompensated adrenal insufficiency, severe general and mental illness, removal of the gallbladder, significant physical exertion, hemodialysis, lead poisoning; taking drugs - anticonvulsants, neuroleptics, beta-blockers, iodides, morphine, prednisolone, radiopaque agents. |
Toxic goiter, thyrotoxicosis; insufficient blood supply to the pituitary gland; trauma, starvation, stress, depression, severe mental illness; taking drugs - T3 and T4, somatostatin, corticosteroids, anabolic steroids, cytostatics, beta-agonists, treatment of hyperprolactinemia. |
With the help of this data, you can decipher your own test results, but it is better to contact a specialist.
