The thyroid gland and its functions, normal hormone levels. Thyroid gland - thyroid functions, diseases and treatment. Features of the structure and functions of the thyroid gland in women

Introduction

Thyroid gland, gland internal secretion, similar in shape to a butterfly, is a unique organ.

Ancient physician-philosophers associated it with fire, thereby emphasizing its importance for the body. Very small in size, no more than 18 ml in women and 25 ml in men, it is involved in almost all life processes. Without it, the functioning of the human body is impossible. Growth and development, metabolic processes, breathing, digestion... Violation of the thyroid gland creates many problems in the functioning of all body systems.

In recent years, the number of people with identified disorders of the thyroid gland has increased sharply: diffuse and nodular goiter, Graves' disease, autoimmune thyroiditis, cancer. There are enough reasons for the disappointing statistics: deteriorating environmental conditions, decreased immune defense of the human body, iodine deficiency, lack of planned medical prevention, unbalanced nutrition, stress as a provoking factor. Currently, thyroid diseases are leaders in the list of diseases endocrine system.

Quite a lot has been written about the treatment and prevention of thyroid diseases; on the Internet you can find tips and recommendations for combating the disease. However, it should be remembered that treatment, selection and prescription of medications should be carried out by a specialist - an endocrinologist. And before you start using any treatment method, you need to consult a doctor.

In this book we will talk about the structural features of the thyroid gland, its functions, diseases of this vital organ, as well as give useful tips and talk about methods for examining and treating thyroid diseases.

Chapter 1 Thyroid gland

The “butterfly” flies to iodine, without it it cannot fly!

The thyroid gland and its functions

The thyroid gland is a gland of the endocrine system that stores iodine and produces iodine-containing hormones: thyroxine And triiodothyronine, which are involved in the regulation of metabolism and growth of individual cells, as well as the body as a whole.

The gland, along with other organs of the endocrine system, performs its main function: maintaining the constancy of the internal environment of the body, necessary for its normal functioning.

The thyroid gland is located under the thyroid cartilage and is shaped like a butterfly (see Fig. 1).

Rice. 1. The shape of the thyroid gland can be compared to the letter “H” or to a butterfly.

Interesting fact:

A brief morphological description of the thyroid gland back in the 2nd century. BC e. given by Galen. He considered it part of the vocal apparatus.

Vesalius continued his study of the thyroid gland.

And the name of this organ was given by Barton in 1656. He proceeded from its shape and purpose: it, like a shield, protects the organs located on the neck.

King formulated the concept of the internal secretion function performed by the thyroid gland.

Carling later described cretinism in people without a thyroid gland.

The gland consists of two lobes and an isthmus. The isthmus is a part of the thyroid tissue that connects the right and left lobes. It is located at the level of the second or third ring of the trachea.

The lateral lobes cover the trachea and are attached to it connective tissue.

An additional, pyramidal lobe may extend from the isthmus or one of the lobes. It is a long process that reaches the upper part of the thyroid cartilage or hyoid bone.

The additional share is not considered a deviation; rather, it is an individual feature of the body (see Fig. 2).

The thyroid gland is located in the middle third of the neck. Run your hand over your neck and you'll find dense cartilage that moves when you swallow. This is the thyroid cartilage. In men it is larger than in women and is called the Adam's apple.

Rice. 2. The lower parts of the thyroid gland are short and wide, and the upper parts are tall, narrow and slightly divergent

The thyroid cartilage somewhat covers the thyroid gland, its upper pole reaches it. It got its name from its functions: it serves as a shield and covers important organs lying on the neck.

Main characteristics of the gland: weight, height and width of lobes, volume.

The thyroid gland of an adult weighs on average 20–40 g, and in a newborn it weighs only 2–3 g.

Normally, the height and width of the thyroid lobes are 3–4 and 1–2 cm, respectively, and the width is 7–11 cm.

In order to understand whether the thyroid gland is enlarged, the doctor palpates (feels) it and compares the size of each of its parts with the size of the terminal nail phalanx of the thumb on the patient’s hand. Normally, their sizes should be the same.

Look at your fingers and you will understand what size your thyroid gland should be (see Fig. 3).

Rice. 3. Nail phalanx of the thumb

The World Health Organization (WHO) distinguishes three grades of thyroid size, which the doctor evaluates during examination and palpation (Table 1).

Table 1

Grades of thyroid size

If a goiter is detected, you should understand what the volume of the thyroid gland is. This is important for further treatment planning and monitoring.

Volume is the main indicator of the size of the thyroid gland.

Normally, it is up to 18 ml in women and up to 25 ml in men.

The volume of the thyroid gland is calculated using a special formula during ultrasound examination (ultrasound).

The thyroid gland “consists” of follicles. Follicles are communities of thyrocytes (thyroid cells), these are closed hollow formations of various shapes. Their walls are formed by cells that produce colloid, a thick, mucous, yellowish liquid.

The smallest follicles have a diameter from 0.03 to 0.1 mm, and their average size is 0.15 mm. The largest follicles can be seen with the naked eye on a cross section of the thyroid gland.

Thyroid hormones

The thyroid gland is an endocrine gland. Its main function is the production of hormones, which contain iodine, without which the normal functioning of the body is impossible (Fig. 4).

Thyroid hormones control metabolism, maturation processes of tissues and organs, and activate mental activity. They are necessary for active growth, the formation of skeletal bones, and in women - for the development of mammary glands.

The term “hormone” translated from Greek means “excite”, “encourage”. It was introduced into medical practice by Bayliss and Starling. Thyroxine was discovered by the American E. Kendall in 1914, and in 1927 C. Garrington first synthesized it. When the production of thyroid hormones decreases in childhood growth of the body stops. In this case, you should immediately consult a doctor!

As already mentioned, the thyroid gland produces thyroid hormones: thyroxine and triiodothyronine.

Thyroxine is also called T4 because it contains four iodine atoms. In the blood and tissues of the human body, the T4 hormone is converted into the T3 hormone - triiodothyronine, which carries three iodine atoms.

Initially, the thyroid gland produces 70% T4 and 30% T3, but the bulk of T3 is formed during the breakdown of T4 in the body.

The biological effect of hormones is realized as follows: the hormone attaches to the receptor and, connecting with it, triggers a series of reactions already in the organ cell.

Since thyroid hormones are responsible for the development of the body, proper metabolism and energy, receptors are everywhere: in the brain and in all tissues of the human body.

The functions of thyroid hormones are as follows:

Increase the intensity of oxidative reactions in cells;

Rice. 4. The main function of the thyroid gland is the production of hormones, without which normal functioning of the body is impossible.

They influence the processes occurring in mitochondria and the cell membrane;

Supports hormonal excitability of the main nerve centers;

Participate in the normal functioning of the heart muscle;

Ensure functioning immune system: stimulate the formation of T-lymphocytes responsible for fighting infection.

The thyroid gland is actively supplied with blood; it has a lot of blood vessels.

Active blood supply is provided by four main arteries. The two superior thyroid arteries arise from

external carotid, and the two lower ones - from the thyroid-cervical subclavian arteries.

The outflow of blood from the gland occurs through paired veins. It is 4–6 ml/min/g and is slightly higher than the blood flow in the kidneys and brain.

Previously, the active blood supply to the thyroid gland created difficulties when performing surgery on this organ. Surgeon Theodor Kocher developed safe approaches to thyroid surgery, for which he received Nobel Prize. And it was knowledge of the peculiarities of the blood supply to the thyroid gland that helped him develop certain surgical tactics. - o

ENDOCRINE SYSTEM

The thyroid gland (TG) is a small organ weighing 15-20 g, located on the front surface of the neck. Together with other glands, it is part of endocrine system- a system of organs that produce biologically active substances - hormones. Throughout life, hormones play a critical role in almost every process that occurs in our body. All glands of the endocrine system closely interact with each other, which explains the fact that even with a slight shift in the function of one organ, changes occur throughout the body.

Hormones, released into the bloodstream by endocrine glands, act on tissues and organs of the body, which are often located at a considerable distance from the place of their formation. The main function of hormones and the entire endocrine system is to maintain homeostasis- normal values ​​of various substances in the blood and, thus, all processes occurring in the body.

Endocrine glands are located in various parts of the body. Thus, the pituitary gland is part of the brain, the thyroid and parathyroid glands are located in the neck, the thymus is in the upper chest, the adrenal glands and pancreas are in the retroperitoneum, and the gonads are in the pelvic cavity. These glands produce and release more than 50 hormones into the blood. The “conductor” for the entire endocrine system is hypothalamic-pituitary system.

Known big number diseases of the endocrine glands. However, almost all of them can be grouped into three large groups. So (1), gland activity may decrease, which is accompanied by a decrease in hormone levels in the blood. In the case of thyroid diseases, we are talking about hypothyroidism (“hypo” means a decrease, a small amount), that is, a decrease in the level of thyroid hormones. On the other hand (2), Gland activity and hormone levels may increase. In diseases of the thyroid gland we are talking about thyrotoxicosis- persistent pathological increase in thyroid function. And finally, many endocrine diseases and most thyroid diseases (3) occur without changes in the function of the endocrine glands.

Most hormones have receptors on the cells of their “target organs”. In this case, the specificity of the action of hormones is explained by their high affinity for the receptor. Most hormones fit into their receptors like a “key to a lock.”

The activity of the endocrine glands is regulated depending on the needs of the body. This is also carried out using receptors found on many cells. They detect small changes in the levels of various substances in the blood and transmit a signal to the endocrine glands. Those, in turn, change their activity so that the level of the original substance returns to normal. Upon reaching this normal value, activity endocrine gland also returns to its previous level. According to this principle, the body regulates the levels of various substances throughout life.

THYROID

The thyroid gland is shaped like a butterfly and is located on the neck in front of the trachea and below the larynx. It consists of two lobes connected by an isthmus. Often young and skinny people The thyroid gland can be seen. The thyroid gland can be palpated in most people, with the exception of people with developed neck muscles and tissue.

Thyroid tissue consists of two types of cells that produce hormones. Most of them are cells that secrete thyroid hormones into the blood - thyroid hormones - thyroxine(T 4) and triiodothyronine(T 3). The latter got their names from the number of iodine atoms in their molecules.

Thyroid function is under the control of the hypothalamic-pituitary system. The hypothalamus synthesizes a substance that regulates the activity of the thyroid gland - thyrotropin-releasing hormone(TRG). This hormone, entering the pituitary gland, leads to the production of thyroid-stimulating hormone(TSH), which stimulates the activity of the thyroid gland and the formation of T 4 and T 3. Of these, the main hormone is T4. Reaching its “target organs”, it turns into T3, which directly affects the cell.

In the blood, most of the thyroid hormones are bound to the carrier protein and are inactive, while only a small free fraction of hormones is active and performs its functions. Some medications, including contraception, can affect the level of carrier protein in the blood, etc. on the level of hormones associated with it. In the past when determining general levels hormones, this distorted the results of hormonal studies. Currently, as a rule, only the amount of free hormones in the blood is determined.

Another type of cell found in the thyroid gland produces and releases another hormone into the blood - calcitonin. It is involved in regulating calcium levels in the body, which is the main material for building bones, as well as necessary substance to conduct impulses in nerve and muscle tissue.

ROLE OF THE THYROID GLAND IN THE BODY

Despite small size The thyroid gland and the hormones produced in it are involved in almost all processes of the body. Its main function is to maintain normal metabolism(metabolism) in the cells of the body. Thyroid hormones stimulate metabolism in almost all cells and regulate almost every process in the body - breathing, eating, sleep, movement, as well as processes in internal organs - from the heartbeat to the functioning of the reproductive system.

Thyroid hormones are necessary for normal mental and physical development. Along with growth hormone produced in the pituitary gland, they are responsible for normal development skeleton bones. A lack of thyroid hormones in childhood leads to cessation of growth, and their deficiency during pregnancy leads to underdevelopment of the brain of the unborn child.

In healthy people, the thyroid gland also takes part in body weight control. At increased consumption food, its activity increases, the formation of T 3 increases, which leads to an increase in the metabolic rate in the body. On the contrary, with malnutrition, thyroid activity decreases, leading to a slowdown in metabolism.

Thyroid hormones take part in regulation of water-salt balance, in the education of some vitamins(for example, the formation of vitamin A in the liver), as well as in the function of other hormones in the body. For example, without thyroid hormones the effect of growth hormone on the brain is impossible.

The role of the thyroid gland in the normal development of the mammary glands in women has been proven. The thyroid gland plays an important role in the functioning of the body's immune system. Its hormones stimulate immune system cells called T cells, which the body uses to fight infection. It is assumed that changes in thyroid function play an important role in the aging of the body.

ENLARGATION OF THE THYROID GLAND

Quite often, patients with thyroid diseases have a goiter - an enlargement of the organ above acceptable values ​​(the normal volume in men is 9-25 ml, in women - 9-18 ml; can be determined using ultrasound). Normally, the thyroid gland enlarges slightly adolescence, during pregnancy, as well as after menopause. Depending on whether the entire organ or a separate part of it is enlarged, they are distinguished accordingly diffuse or nodal goiter. Below are some diseases accompanied by the development of goiter:

• endemic (diffuse euthyroid) goiter - a disease caused by a lack of iodine in the environment
• diffuse toxic goiter (Graves-Bazedow disease) - a disease accompanied by increased thyroid activity
• thyroiditis (goiter) Hashimoto's - autoimmune disease, often leading to insufficient thyroid function
• goiter while taking thyreostatic drugs (thiamazole, etc.), some food supplements and vitamins
• thyroid adenoma - benign tumor thyroid gland
• thyroid cancer - malignant tumor of the thyroid gland

The functions of the thyroid gland in the human body are very diverse.

Most people try to diagnose themselves, but first of all it doesn’t hurt to figure out what functions the thyroid gland performs.

Thyroid diseases, unfortunately, are quite common and most often occur during childbearing years.

In reality, few people realize that they have such pathologies. And some do not even know about such an organ, or know little about it.

Location of the thyroid gland

To continue examining the functions of the thyroid gland, you first need to know where it is located.

The shape of the thyroid gland is similar to a butterfly, and is located on the surface in front of the neck. This organ is well supplied with blood, and hormones are released into the blood.

The gland mainly consists of hormones, which are where hormones are synthesized.

The supply of some of the hormones occurs in the form of a colloid, and it, in fact, is located in the follicles. As needed, hormones are sent from the colloid into the blood.

What is necessary for normal operation

For proper operation An organ, first of all, needs iodine; if there is not enough of it, iodine deficiency disease may appear, for example.

But it happens that problems with the thyroid gland do not appear at all due to iodine deficiency.

Selenium and zinc are no less important for the thyroid gland. Due to their lack or excess.

The thyroid gland and its functions

What function do thyroid hormones perform? Thyroid hormones function as regulators of the metabolic process.

The entire metabolism in the body depends on hormones, and main function- This is the main exchange.

Let’s try to give a clear definition of “basal metabolism” - this is the minimum energy that the human body needs for proper functioning at rest.

Simply put, this is the number of calories spent on the work of the most important organs.

If speak about motor activity, or brain activity, then these processes require additional energy provided by other processes.

Thyroid hormones carry out the main metabolism, but if they are too much, the body’s functioning may malfunction, and protein and fat metabolism will suffer.

This is a very variable value that changes regularly depending on nutrition and stress on the body. The metabolic rate can be increased slightly, but it will still decrease with age.

The role of the thyroid gland in a woman’s body

If we talk about the energy consumption of human organs, the most expensive are the brain, all intra-abdominal organs, and especially muscles.

And the bones and adipose tissue have rather slow metabolic processes.

So, in women these processes do not go through these processes so intensely, but it contributes to following features: women have less in their bodies muscle mass, and a little more fat.

As a result, women need to spend fewer calories on basal metabolism.

The function of the thyroid gland in a woman’s body is, first of all, a normal hormonal balance.

Conclusion: The thyroid gland occupies a leading place at all stages of the body’s growth, right from the embryonic period. A person’s development greatly depends on the functionality and condition of the thyroid gland.

Thyroid in men

The role of the thyroid gland in a man’s body is also the normalization of hormones. If there are problems with thyroid hormones, the level of thyroid hormones increases, which causes weakness, irritability, and sometimes weight loss.

If you have problems with the thyroid gland, the level of hormones may drop significantly, and metabolic processes will also regularly decrease. Because of this, the skin begins to dry out.

Insufficient thyroid function

Proper functioning of the thyroid gland is the key to the health of the whole body.

When the functioning of the thyroid gland deteriorates, the basal metabolism decreases, energy is not consumed, the organs experience a lack of energy, and because of this you feel unwell:

1. Depression and lethargy.
2. Weakened muscles.
3. Decreased intestinal tone, possible constipation.
4. Memory impairment.
5. Low blood pressure and slow heartbeat.
6. Swelling.
7. Weight gain.

Increased thyroid function

Studies have confirmed that patients with diabetes have thyroid pathologies 20% more often.

Besides this, there is also inverse relationship. If you have problems with the thyroid gland before the onset of diabetes, they negatively affect the further course of diabetes.

Treatment

Whether you have problems with the thyroid gland or not, you will not understand without contacting an endocrinologist.

The thyroid gland performs special functions in the body, and incorrectly prescribed treatment often leads to unpleasant consequences.

A correct diagnosis will help

Thyroid cyst

Often, you can also get rid of a cyst folk method, namely by taking tincture of bait and various compresses.

Don't forget about this important body like the thyroid gland. Her work is significantly important for people. Have you been diagnosed?

It consists of two lobes and an isthmus and is located in front of the larynx. The mass of the thyroid gland is 30 g.

The main structural and functional unit of the gland is follicles - rounded cavities, the wall of which is formed by one row of cells cuboidal epithelium. Follicles are filled with colloid and contain hormones thyroxine And triiodothyronine, which are bound to the protein thyroglobulin. In the interfollicular space there are C-cells that produce the hormone thyrocalcitonin. The gland is richly supplied with blood and lymphatic vessels. The amount of water flowing through the thyroid gland in 1 minute is 3-7 times higher than the mass of the gland itself.

Biosynthesis of thyroxine and triiodothyronine is carried out due to iodization of the amino acid tyrosine, therefore, active absorption of iodine occurs in the thyroid gland. The iodine content in the follicles is 30 times higher than its concentration in the blood, and with hyperfunction of the thyroid gland this ratio becomes even greater. Iodine absorption occurs through active transport. After combining tyrosine, which is part of thyroglobulin, with atomic iodine, monoiodotyrosine and diiodotyrosine are formed. By combining two molecules of diiodotyrosine, tetraiodothyronine, or thyroxine, is formed; condensation of mono- and diiodotyrosine leads to the formation of triiodothyronine. Subsequently, as a result of the action of proteases that break down thyroglobulin, active hormones are released into the blood.

The activity of thyroxine is several times less than that of triiodothyronine, but the content of thyroxine in the blood is approximately 20 times greater than triiodothyronine. Thyroxine, when deiodinated, can be converted into triiodothyronine. Based on these facts, it is assumed that the main thyroid hormone is triiodothyronine, and thyroxine functions as its precursor.

The synthesis of hormones is inextricably linked with the intake of iodine into the body. If there is a deficiency of iodine in the water and soil in the region of residence, there is also little iodine in food products of plant and animal origin. In this case, in order to ensure sufficient synthesis of the hormone, the thyroid gland of children and adults increases in size, sometimes very significantly, i.e. goiter occurs. The increase can be not only compensatory, but also pathological, it is called endemic goiter. The lack of iodine in the diet is best compensated for seaweed and other seafood, iodized salt, dining room mineral water, containing iodine, baked goods with iodine additives. However, excessive intake of iodine into the body puts a strain on the thyroid gland and can lead to serious consequences.

Thyroid hormones

Effects of thyroxine and triiodothyronine

Basic:

• activate the genetic apparatus of the cell, stimulate metabolism, oxygen consumption and the intensity of oxidative processes

Metabolic:

• protein metabolism: stimulate protein synthesis, but when the level of hormones exceeds the norm, catabolism predominates;
• fat metabolism: stimulate lipolysis;
• carbohydrate metabolism: during overproduction, glycogenolysis is stimulated, blood glucose levels increase, its entry into cells is activated, liver insulinase is activated

Functional:

• ensure the development and differentiation of tissues, especially nervous;
• enhance the effects of the sympathetic nervous system by increasing the number of adrenergic receptors and inhibiting monoamine oxidase;
• prosympathetic effects are manifested in an increase in heart rate, systolic volume, blood pressure, respiratory rate, intestinal motility, central nervous system excitability, and increased body temperature

Manifestations of changes in the production of thyroxine and triiodothyronine

Comparative characteristics of insufficient production of somatotropin and thyroxine

The effect of thyroid hormones on body functions

The characteristic effect of thyroid hormones (thyroxine and triiodothyronine) is to increase energy metabolism. Introduction is always accompanied by an increase in oxygen consumption, and removal of the thyroid gland is always accompanied by a decrease. When the hormone is administered, metabolism increases, the amount of energy released increases, and body temperature rises.

Thyroxine increases consumption. Weight loss and intensive tissue consumption of glucose from the blood occur. The loss of glucose from the blood is compensated by its replenishment due to the increased breakdown of glycogen in the liver and muscles. Lipid reserves in the liver are reduced, and the amount of cholesterol in the blood decreases. The excretion of water, calcium and phosphorus from the body increases.

Thyroid hormones cause increased excitability, irritability, insomnia, and emotional imbalance.

Thyroxine increases minute blood volume and heart rate. Thyroid hormone is necessary for ovulation, it helps maintain pregnancy, and regulates the function of the mammary glands.

The growth and development of the body is also regulated by the thyroid gland: a decrease in its function causes growth to stop. Thyroid hormone stimulates hematopoiesis, increases gastric and intestinal secretions and milk secretion.

In addition to iodine-containing hormones, the thyroid gland produces thyrocalcitonin, reducing calcium levels in the blood. Thyrocalcitonin is an antagonist of parathyroid hormone of the parathyroid glands. Thyroid calcitonin acts on bone tissue, enhances the activity of osteoblasts and the mineralization process. In the kidneys and intestines, the hormone inhibits the reabsorption of calcium and stimulates the reabsorption of phosphates. The implementation of these effects leads to hypocalcemia.

Hyper- and hypofunction of the gland

Hyperfunction (hyperthyroidism) causes a disease called Graves' disease. The main symptoms of the disease: goiter, bulging eyes, increased metabolism, heart rate, increased sweating, physical activity (fussiness), irritability (moody, rapid mood swings, emotional instability), fast fatiguability. A goiter is formed due to diffuse enlargement of the thyroid gland. Treatment methods are now so effective that severe cases diseases are quite rare.

Hypofunction (hypothyroidism) thyroid gland, which occurs in early age, up to 3-4 years, causes the development of symptoms cretinism. Children suffering from cretinism are delayed in physical and mental development. Symptoms of the disease: dwarf stature and abnormal body proportions, a wide, deeply sunken bridge of the nose, widely spaced eyes, an open mouth and a constantly protruding tongue, as it does not fit in the mouth, short and curved limbs, a dull facial expression. The life expectancy of such people usually does not exceed 30-40 years. In the first 2-3 months of life, subsequent normal mental development. If treatment begins in one year old, then 40% of children exposed to this disease remain at a very low level of mental development.

Hypofunction of the thyroid gland in adults leads to a disease called myxedema, or mucous swelling. With this disease, the intensity decreases metabolic processes(by 15-40%), body temperature, pulse becomes less frequent, blood pressure decreases, swelling appears, hair falls out, nails break, the face becomes pale, lifeless, and mask-like. Patients are characterized by slowness, drowsiness, and poor memory. Myxedema is a slowly progressive disease that, if left untreated, leads to complete disability.

Regulation of thyroid function

A specific regulator of the thyroid gland is iodine, the thyroid hormone itself and TSH (Thyroid Stimulating Hormone). Iodine in small doses increases TSH secretion, and in large doses inhibits it. The thyroid gland is under the control of the central nervous system. Foods such as cabbage, rutabaga, and turnips suppress thyroid function. The production of thyroxine and triiodothyronine increases sharply under conditions of prolonged emotional arousal. It is also noted that the secretion of these hormones accelerates with a decrease in body temperature.

Manifestations of endocrine thyroid function disorders

With an increase in the functional activity of the thyroid gland and excess production of thyroid hormones, a condition occurs hyperthyroidism (hyperthyroidism), characterized by an increase in the level of thyroid hormones in the blood. The manifestations of this condition are explained by the effects of thyrsoid hormones in elevated concentrations. Thus, due to an increase in basal metabolism (hypermetabolism), patients experience a slight increase in body temperature (hyperthermia). Body weight decreases despite preserved or increased appetite. This condition is manifested by an increase in oxygen demand, tachycardia, increased myocardial contractility, increased systolic blood pressure, and increased ventilation. The activity of the ATP increases, the number of β-adrenoreceptors increases, sweating and heat intolerance develop. Increased excitability and emotional lability, tremor of the limbs and other changes in the body may appear.

Increased formation and secretion of thyroid hormones can be caused by a number of factors, the correct identification of which determines the choice of method for correcting thyroid function. Among them are factors that cause hyperfunction of the follicular cells of the thyroid gland (tumors of the gland, mutation of G-proteins) and an increase in the formation and secretion of thyroid hormones. Hyperfunction of thyrocytes is observed with excessive stimulation of thyrotropin receptors by an increased content of TSH, for example, with pituitary tumors, or reduced sensitivity of thyrotropin hormone receptors in the thyrotrophs of the adenohypophysis. A common cause of hyperfunction of thyrocytes and an increase in the size of the gland is stimulation of TSH receptors by antibodies produced to them in an autoimmune disease called Graves-Bazedow disease (Fig. 1). A temporary increase in the level of thyrsoid hormones in the blood can develop when thyrocytes are destroyed due to inflammatory processes in the gland (toxic Hashimoto's thyroiditis), taking excessive amounts of thyroid hormones and iodine preparations.

Increased thyroid hormone levels may occur thyrotoxicosis; in this case they talk about hyperthyroidism with thyrotoxicosis. But thyrotoxicosis can develop when an excess amount of thyroid hormones is introduced into the body in the absence of hyperthyroidism. The development of thyrotoxicosis due to increased sensitivity of cell receptors to thyroid hormones has been described. There are also known opposite cases, when the sensitivity of cells to thyroid hormones is reduced and a state of resistance to thyroid hormones develops.

Reduced formation and secretion of thyroid hormones can be caused by many reasons, some of which are a consequence of disruption of the mechanisms regulating the function of the thyroid gland. So, hypothyroidism (hypothyroidism) can develop with a decrease in the formation of TRH in the hypothalamus (tumors, cysts, radiation, encephalitis in the hypothalamus, etc.). This hypothyroidism is called tertiary. Secondary hypothyroidism develops due to insufficient production of TSH by the pituitary gland (tumors, cysts, radiation, surgical removal of part of the pituitary gland, encephalitis, etc.). Primary hypothyroidism can develop as a result of autoimmune inflammation of the gland, with a deficiency of iodine, selenium, excessive intake of goitrogens - goitrogens (some varieties of cabbage), after irradiation of the gland, long-term use a number of medications (iodine, lithium, antithyroid drugs), etc.

Rice. 1. Diffuse enlargement of the thyroid gland in a 12-year-old girl with autoimmune thyroiditis(T. Foley, 2002)

Insufficient production of thyroid hormones leads to a decrease in metabolic rate, oxygen consumption, ventilation, myocardial contractility and minute blood volume. Severe hypothyroidism may develop a condition called myxedema — mucous swelling. It develops due to the accumulation (possibly under the influence of elevated TSH levels) of mucopolysaccharides and water in the basal layers of the skin, which leads to facial puffiness and pasty skin consistency, as well as increased body weight, despite decreased appetite. Patients with myxedema may develop mental and motor retardation, drowsiness, chilliness, decreased intelligence, decreased tone of the sympathetic section of the ANS and other changes.

In implementation complex processes The formation of thyroid hormones involves ion pumps that ensure the supply of iodine and a number of protein enzymes, among which thyroid peroxidase plays a key role. In some cases, a person may have a genetic defect leading to a disruption of their structure and function, which is accompanied by a disruption in the synthesis of thyroid hormones. Genetic defects in the structure of thyroglobulin may be observed. Autoantibodies are often produced against thyroid peroxidase and thyroglobulin, which is also accompanied by a disruption in the synthesis of thyroid hormones. The activity of the processes of iodine uptake and its inclusion in thyroglobulin can be influenced by a number of pharmacological agents, regulating the synthesis of hormones. Their synthesis can be influenced by taking iodine preparations.

The development of hypothyroidism in the fetus and newborns can lead to cretinism - physical (short stature, imbalance of body proportions), sexual and mental underdevelopment. These changes can be prevented by adequate thyroid hormone replacement therapy in the first months after birth.

Structure of the thyroid gland

It is the largest in terms of mass and size endocrine organ. It usually consists of two lobes connected by an isthmus and is located on the anterior surface of the neck, being fixed to the anterior and lateral surfaces of the trachea and larynx by connective tissue. Average weight The normal thyroid gland in adults ranges from 15-30 g, but its size, shape and topography of location vary widely.

The functionally active thyroid gland is the first of the endocrine glands to appear during embryogenesis. The thyroid gland in the human fetus is formed on the 16-17th day of intrauterine development in the form of an accumulation of endodermal cells at the root of the tongue.

On early stages development (6-8 weeks), the gland primordium is a layer of intensively proliferating epithelial cells. During this period there is fast growth gland, but hormones are not yet formed in it. The first signs of their secretion are detected at 10-11 weeks (in fetuses about 7 cm in size), when the gland cells are already able to absorb iodine, form a colloid and synthesize thyroxine.

Single follicles appear under the capsule, in which follicular cells form.

Parafollicular (parafollicular) or C-cells grow into the thyroid rudiment from the 5th pair of gill pouches. By the 12-14th weeks of fetal development, the entire right lobe of the thyroid gland acquires a follicular structure, and the left one two weeks later. By 16-17 weeks, the fetal thyroid gland is already fully differentiated. The thyroid glands of fetuses 21-32 weeks of age are characterized by high functional activity, which continues to increase until 33-35 weeks.

In the parenchyma of the gland there are three types of cells: A, B and C. The bulk of parenchyma cells are thyrocytes (follicular, or A-cells). They line the wall of the follicles, in the cavities of which the colloid is located. Each follicle is surrounded by a dense network of capillaries, into the lumen of which thyroxine and triiodothyronine secreted by the thyroid gland are absorbed.

In the unchanged thyroid gland, the follicles are evenly distributed throughout the parenchyma. When the functional activity of the gland is low, thyrocytes are usually flat; when the functional activity is high, they are cylindrical (the height of the cells is proportional to the degree of activity of the processes occurring in them). The colloid that fills the lumens of the follicles is a homogeneous viscous liquid. The bulk of the colloid is thyroglobulin, secreted by thyrocytes into the lumen of the follicle.

B cells (Ashkenazi-Hurthle cells) are larger than thyrocytes, have eosinophilic cytoplasm and a round, centrally located nucleus. Biogenic amines, including serotonin, were found in the cytoplasm of these cells. B cells first appear at the age of 14-16 years. IN large quantities they occur in people aged 50-60 years.

Parafollicular, or C-cells (in Russian transcription K-cells), differ from thyrocytes in the lack of the ability to absorb iodine. They provide the synthesis of calcitonin, a hormone involved in the regulation of calcium metabolism in the body. C-cells are larger than thyrocytes and are usually located singly within follicles. Their morphology is characteristic of cells that synthesize protein for export (a rough endoplasmic reticulum, Golgi complex, secretory granules, and mitochondria are present). On histological preparations, the cytoplasm of C-cells appears lighter than the cytoplasm of thyrocytes, hence their name - light cells.

If at the tissue level the main structural and functional unit of the thyroid gland is follicles surrounded by basement membranes, then one of the putative organ units of the thyroid gland may be microlobules, which include follicles, C-cells, hemocapillaries, and tissue basophils. The microlobule consists of 4-6 follicles surrounded by a membrane of fibroblasts.

By the time of birth, the thyroid gland is functionally active and structurally fully differentiated. In newborns, the follicles are small (60-70 microns in diameter); as the child’s body develops, their size increases and reaches 250 microns in adults. In the first two weeks after birth, the follicles develop intensively; by 6 months they are well developed throughout the gland, and by one year they reach a diameter of 100 microns. During puberty, there is an increase in the growth of the parenchyma and stroma of the gland, an increase in its functional activity, manifested by an increase in the height of thyrocytes and an increase in enzyme activity in them.

In an adult, the thyroid gland is adjacent to the larynx and the upper part of the trachea in such a way that the isthmus is located at the level of the II-IV tracheal semirings.

The weight and size of the thyroid gland changes throughout life. U healthy newborn the mass of the gland varies from 1.5 to 2 g. By the end of the first year of life, the mass doubles and slowly increases by the period of puberty up to 10-14 g. The increase in mass is especially noticeable at the age of 5-7 years. The weight of the thyroid gland at the age of 20-60 years ranges from 17 to 40 g.

The thyroid gland has an exceptionally abundant blood supply compared to other organs. The volumetric flow rate of blood in the thyroid gland is about 5 ml/g per minute.

The thyroid gland is supplied with blood by paired superior and inferior thyroid arteries. Sometimes the unpaired, most inferior artery(a. thyroideaima).

Outflow venous blood from the thyroid gland is carried out through veins that form plexuses around the lateral lobes and the isthmus. The thyroid gland has an extensive network of lymphatic vessels, through which the lymph flows into the deep cervical lymph nodes, then into the supraclavicular and lateral cervical deep lymph nodes. Endurant lymphatic vessels lateral cervical deep lymph nodes form on each side of the neck a jugular trunk, which flows into the left thoracic duct, and on the right - into the right lymphatic duct.

The thyroid gland is innervated by postganglionic fibers of the sympathetic nervous system from the upper, middle (mainly) and lower cervical nodes sympathetic trunk. The thyroid nerves form plexuses around the vessels approaching the gland. These nerves are believed to perform a vasomotor function. Also involved in the innervation of the thyroid gland nervus vagus, carrying parasympathetic fibers to the gland as part of the superior and inferior laryngeal nerves. The synthesis of iodine-containing thyroid hormones T 3 and T 4 is carried out by follicular A-cells - thyrocytes. Hormones T 3 and T 4 are iodinated.

Hormones T 4 and T 3 are iodinated derivatives of the amino acid L-tyrosine. Iodine, which is part of their structure, makes up 59-65% of the mass of the hormone molecule. The iodine requirement for normal synthesis of thyroid hormones is presented in table. 1. The sequence of synthesis processes is simplified as follows. Iodine in the form of iodide is captured from the blood using an ion pump, accumulates in thyrocytes, is oxidized and incorporated into the phenolic ring of tyrosine in thyroglobulin (iodine organization). Iodination of thyroglobulin with the formation of mono- and diiodotyrosines occurs at the boundary between thyrocyte and colloid. Next, the connection (condensation) of two diiodotyrosine molecules is carried out to form T 4 or diiodotyrosine and monoiodotyrosine to form T 3 . Some of the thyroxine undergoes deiodination in the thyroid gland to form triiodothyronine.

Table 1. Iodine consumption standards (WHO, 2005. according to I. Dedov et al. 2007)

Iodinated thyroglobulin, together with T4 and T3 attached to it, accumulates and is stored in the follicles in the form of a colloid, acting as depot thyroid hormones. The release of hormones occurs as a result of pinocytosis of the follicular colloid and subsequent hydrolysis of thyroglobulin in phagolysosomes. The released T 4 and T 3 are secreted into the blood.

The basal daily secretion by the thyroid gland is about 80 μg T 4 and 4 μg T 3. At the same time, thyrocytes of the thyroid follicles are the only source formation of endogenous T4. Unlike T4, T3 is formed in small quantities in thyrocytes, and the main formation of this active form of the hormone occurs in the cells of all tissues of the body through deiodination of about 80% of T4.

Thus, in addition to the glandular depot of thyroid hormones, the body has a second, extraglandular depot of thyroid hormones, represented by hormones associated with transport proteins in the blood. The role of these depots is to prevent rapid decline the level of thyroid hormones in the body, which could occur with a short-term decrease in their synthesis, for example, with a short-term decrease in iodine intake. The bound form of hormones in the blood prevents their rapid removal from the body through the kidneys and protects cells from the uncontrolled entry of hormones into them. They enter the cells free hormones in quantities commensurate with their functional needs.

Thyroxine entering the cells undergoes deiodination under the action of deiodinase enzymes, and when one iodine atom is removed, a more active hormone is formed - triiodothyronine. In this case, depending on the deiodination pathways, both active T3 and inactive reverse T3 (3,3",5"-triiodo-L-thyronine - pT3) can be formed from T4. These hormones, through sequential deiodination, are converted into metabolites T2, then T1 and T0, which are conjugated with glucuronic acid or sulfate in the liver and excreted in the bile and through the kidneys from the body. Not only T3, but also other metabolites of thyroxine can also exhibit biological activity.

The mechanism of action of thyrsoid hormones is primarily due to their interaction with nuclear receptors, which are non-histone proteins located directly in the cell nucleus. There are three main subtypes of thyroid hormone receptors: TPβ-2, TPβ-1, and TRA-1. As a result of interaction with T 3, the receptor is activated, the hormone-receptor complex interacts with the hormone-sensitive region of DNA and regulates the transcriptional activity of genes.

A number of non-genomic effects of thyrsoid hormones in mitochondria and the plasma membrane of cells have been identified. In particular, thyroid hormones can change the permeability of mitochondrial membranes for hydrogen protons and, by uncoupling the processes of respiration and phosphorylation, reduce ATP synthesis and increase heat production in the body. They change the permeability of plasma membranes to Ca 2+ ions and influence many intracellular processes carried out with the participation of calcium.

Main effects and role of thyroid hormones

The normal functioning of all organs and tissues of the body without exception is possible with normal levels of thyroid hormones, as they affect the growth and maturation of tissues, energy exchange and the exchange of proteins, lipids, carbohydrates, nucleic acids, vitamins and other substances. There are metabolic and other physiological effects thyroid hormones.

Metabolic effects:

• activation of oxidative processes and an increase in basal metabolism, increased absorption of oxygen by tissues, increased heat generation and body temperature;
• stimulation of protein synthesis (anabolic effect) in physiological concentrations;
• increased oxidation fatty acids and a decrease in their level in the blood;
• hyperglycemia due to activation of glycogenolysis in the liver.

Physiological effects:

• security normal processes growth, development, differentiation of cells, tissues and organs, including the central nervous system (myelination nerve fibers, differentiation of neurons), as well as processes physiological regeneration fabrics;
• enhancing the effects of the SNS through increasing the sensitivity of adrenergic receptors to the action of Adr and NA;
• increased excitability of the central nervous system and activation of mental processes;
• participation in ensuring reproductive function (promote the synthesis of GH, FSH, LH and the implementation of the effects of insulin-like growth factor - IGF);
• participation in the formation of adaptive reactions of the body to adverse effects, in particular cold;
• participation in development muscular system, increasing the strength and speed of muscle contractions.

Regulation of the formation, secretion and transformations of thyroid hormones is carried out by complex hormonal, nervous and other mechanisms. Their knowledge allows us to diagnose the causes of decreased or increased secretion of thyroid hormones.

A key role in the regulation of the secretion of thyroid hormones is played by hormones of the hypothalamic-pituitary-thyroid axis (Fig. 2). Basal secretion of thyroid hormones and its changes under various influences are regulated by the level of TRH of the hypothalamus and TSH of the pituitary gland. TRH stimulates the production of TSH, which has a stimulating effect on almost all processes in the thyroid gland and the secretion of T4 and T3. Under normal physiological conditions, the formation of TRH and TSH is controlled by the level of free T4 and T. in the blood based on the mechanisms of negative feedback. In this case, the secretion of TRH and TSH is inhibited by a high level of thyroid hormones in the blood, and when their concentration is low, it increases.

Rice. 2. Schematic illustration regulation of the formation and secretion of hormones in the hypothalamus-pituitary-thyroid axis

The state of sensitivity of receptors to the action of hormones at various levels of the axis is important in the mechanisms of regulation of hormones of the hypothalamic-pituitary-thyroid axis. Changes in the structure of these receptors or their stimulation by autoantibodies may cause disruption of the formation of thyroid hormones.

The formation of hormones in the gland itself depends on the receipt of a sufficient amount of iodide from the blood - 1-2 mcg per 1 kg of body weight (see Fig. 2).

When there is insufficient intake of iodine into the body, adaptation processes develop in it, which are aimed at the most gentle and efficient use the iodine it contains. They consist of increased blood flow through the gland, more efficient uptake of iodine by the thyroid gland from the blood, changes in the processes of hormone synthesis and Tu secretion. Adaptive reactions are triggered and regulated by thyrotropin, the level of which increases with iodine deficiency. If the daily intake of iodine in the body is less than 20 mcg for a long time, then prolonged stimulation of thyroid cells leads to the proliferation of its tissue and the development of goiter.

The self-regulatory mechanisms of the gland under conditions of iodine deficiency ensure its greater uptake by thyrocytes at a lower level of iodine in the blood and more efficient reutilization. If about 50 mcg of iodine is delivered to the body per day, then due to an increase in the rate of its absorption by thyrocytes from the blood (iodine of food origin and reutilized iodine from metabolic products), about 100 mcg of iodine per day enters the thyroid gland.

Coming from gastrointestinal tract 50 mcg of iodine per day is the threshold at which the long-term ability of the thyroid gland to accumulate it (including reutilized iodine) in quantities when the content of inorganic iodine in the gland remains at the lower limit of normal (about 10 mg). Below this threshold intake of iodine into the body per day, the effectiveness increased speed iodine uptake by the thyroid gland is insufficient, iodine absorption and its content in the gland decrease. In these cases, the development of thyroid dysfunction becomes more likely.

Simultaneously with the activation of the adaptive mechanisms of the thyroid gland in case of iodine deficiency, a decrease in its excretion from the body in the urine is observed. As a result, adaptive excretory mechanisms ensure the removal of iodine from the body per day in quantities equivalent to its lower daily intake from the gastrointestinal tract.

Intake of subthreshold iodine concentrations into the body (less than 50 mcg per day) leads to an increase in the secretion of TSH and its stimulating effect on the thyroid gland. This is accompanied by an acceleration of iodination of tyrosyl residues of thyroglobulin, an increase in the content of monoiodotyrosines (MIT) and a decrease in diiodotyrosines (DIT). The MIT/DIT ratio increases, and, as a result, T4 synthesis decreases and T3 synthesis increases. The T 3 /T 4 ratio increases in iron and blood.

With severe iodine deficiency, there is a decrease in serum T4 levels, an increase in TSH levels and normal or increased content T 3. The mechanisms of these changes are not clearly understood, but most likely they are the result of an increase in the rate of formation and secretion of T 3 , an increase in the T 3 T 4 ratio, and an increase in the conversion of T 4 to T 3 in peripheral tissues.

An increase in the formation of T3 under conditions of iodine deficiency is justified from the point of view of achieving the greatest final metabolic effects of TG with the lowest “iodine” capacity. It is known that the effect on metabolism of T 3 is approximately 3-8 times stronger than T 4, but since T 3 contains only 3 iodine atoms in its structure (and not 4 like T 4), then for the synthesis of one T 3 molecule only 75% of iodine costs are needed, compared to the synthesis of T4.

With a very significant iodine deficiency and decreased thyroid function against the background high level TSH, T 4 and T 3 levels decrease. More thyroglobulin appears in the blood serum, the level of which correlates with the level of TSH.

Iodine deficiency in children has a stronger effect on metabolic processes in the thyrocytes of the thyroid gland than in adults. In iodine-deficient areas of residence, thyroid dysfunction in newborns and children is much more common and more pronounced than in adults.

When a small excess of iodine enters the human body, the degree of iodide organization, TG synthesis and their secretion increase. There is an increase in the level of TSH, a slight decrease in the level of free T4 in the serum with a simultaneous increase in the content of thyroglobulin in it. Longer-term excess iodine intake may block TG synthesis by inhibiting the activity of enzymes involved in biosynthetic processes. By the end of the first month, there is an increase in the size of the thyroid gland. With chronic excessive intake of excess iodine into the body, hypothyroidism may develop, but if the intake of iodine into the body is normalized, then the size and function of the thyroid gland may return to its original values.

Sources of iodine that may cause its excess intake into the body are often iodized salt, complex multivitamin preparations containing mineral supplements, food products and some iodine-containing medicines.

The thyroid gland has an internal regulatory mechanism that allows it to effectively cope with excess iodine intake. Although iodine intake may fluctuate, serum TG and TSH concentrations may remain constant.

It is believed that maximum amount iodine, which, when entering the body, does not yet cause changes in thyroid function, is about 500 mcg per day for adults, but at the same time there is an increase in the level of TSH secretion due to the action of thyrotropin-releasing hormone.

Iodine intake in quantities of 1.5-4.5 mg per day leads to a significant decrease in serum levels of both total and free T4 and an increase in TSH levels (T3 levels remain unchanged).

The effect of suppressing the function of the thyroid gland by excess iodine also occurs in thyrotoxicosis, when by taking an excess amount of iodine (in relation to the natural daily requirement), the symptoms of thyrotoxicosis are eliminated and the serum level of TG is reduced. However, with prolonged intake of excess iodine into the body, the manifestations of thyrotoxicosis return again. It is believed that a temporary decrease in the level of TG in the blood with excess iodine intake is primarily due to inhibition of hormone secretion.

The intake of small excess amounts of iodine into the body leads to a proportional increase in its uptake by the thyroid gland, up to a certain saturating value of absorbed iodine. When this value is reached, iodine uptake by the gland may decrease despite its entry into the body in large quantities. Under these conditions, under the influence of pituitary TSH, the activity of the thyroid gland can vary widely.

Since when excess iodine enters the body TSH level increases, then one would expect not initial suppression, but activation of thyroid function. However, it has been established that iodine inhibits an increase in the activity of adenylate cyclase, suppresses the synthesis of thyroid peroxidase, and inhibits the formation of hydrogen peroxide in response to the action of TSH, although the binding of TSH to the cell membrane receptor of thyrocytes is not impaired.

It has already been noted that the suppression of thyroid function by excess iodine is temporary and the function is soon restored despite the continued intake of excess amounts of iodine into the body. The thyroid gland adapts or escapes from the influence of iodine. One of the main mechanisms of this adaptation is a decrease in the efficiency of iodine uptake and transport into the thyrocyte. Since it is believed that the transport of iodine through the basement membrane of the thyrocyte is associated with the function of Na+/K+ ATPase, it can be expected that excess iodine may affect its properties.

Despite the existence of mechanisms for adaptation of the thyroid gland to insufficient or excess iodine intake, iodine balance must be maintained in the body to maintain its normal function. With a normal level of iodine in soil and water per day, the human body with plant foods and to a lesser extent, up to 500 mcg of iodine can be supplied with water in the form of iodide or iodate, which are converted to iodides in the stomach. Iodides are rapidly absorbed from the gastrointestinal tract and distributed into the extracellular fluid of the body. The concentration of iodide in the extracellular spaces remains low, since part of the iodide is quickly captured from the extracellular fluid by the thyroid gland, and the remaining is excreted from the body at night. The rate of iodine uptake by the thyroid gland is inversely proportional to the rate of its excretion by the kidneys. Iodine can be excreted by the salivary and other glands digestive tract, but is then reabsorbed from the intestine into the blood. About 1-2% of iodine is excreted sweat glands, and with increased sweating, the proportion of iodine released with iota can reach 10%.

From 500 mcg of iodine absorbed from upper sections intestines into the blood, about 115 mcg is captured by the thyroid gland and about 75 mcg of iodine is used per day for the synthesis of TG, 40 mcg is returned back to the extracellular fluid. Synthesized T 4 and T 3 are subsequently destroyed in the liver and other tissues, the iodine released in the amount of 60 mcg enters the blood and extracellular fluid, and about 15 mcg of iodine, conjugated in the liver with glucuronides or sulfates, is excreted in bile.

IN total volume blood is an extracellular fluid that makes up about 35% of an adult’s body weight (or about 25 l), in which about 150 mcg of iodine is dissolved. Iodide is freely filtered in the glomeruli and approximately 70% is passively reabsorbed in the tubules. During the day, about 485 mcg of iodine is excreted from the body in urine and about 15 mcg in feces. The average iodine concentration in blood plasma is maintained at about 0.3 μg/L.

With a decrease in iodine intake into the body, its amount in body fluids decreases, excretion in urine decreases, and the thyroid gland can increase its absorption by 80-90%. The thyroid gland is capable of storing iodine in the form of iodothyronines and iodinated tyrosines in quantities close to the body's 100-day requirement. Due to these iodine-saving mechanisms and stored iodine, TG synthesis under conditions of iodine deficiency in the body can remain unimpaired for a period of up to two months. Longer iodine deficiency in the body leads to a decrease in TG synthesis despite its maximum capture by the gland from the blood. Increasing the intake of iodine into the body can accelerate the synthesis of TG. However, if daily iodine intake exceeds 2000 mcg, iodine accumulation in the thyroid gland reaches a level where iodine uptake and hormone biosynthesis are inhibited. Chronic iodine intoxication occurs when the daily intake of iodine into the body is more than 20 times the daily requirement.

Iodide entering the body is excreted mainly through urine, therefore its total content in the volume of daily urine is the most accurate indicator of iodine intake and can be used to assess the iodine balance in the whole organism.

Thus, a sufficient supply of exogenous iodine is necessary for the synthesis of TG in quantities adequate to the needs of the body. Moreover, the normal implementation of the effects of TG depends on the effectiveness of their binding to nuclear receptors of cells, which contain zinc. Consequently, the intake of a sufficient amount of this trace element (15 mg/day) into the body is also important for the manifestation of the effects of TG at the level of the cell nucleus.

The formation of active forms of TG from thyroxine in peripheral tissues occurs under the action of deiodinases, the manifestation of which activity requires the presence of selenium. It has been established that the intake of selenium into the body of an adult in quantities of 55-70 mcg per day is a necessary condition for the formation of a sufficient amount of T v in peripheral tissues

The nervous mechanisms of regulation of thyroid function are carried out through the influence of the neurotransmitters SPS and PSNS. The SNS innervates glandular vessels and glandular tissue with its postganglionic fibers. Norepinephrine increases the level of cAMP in thyrocytes, enhances their absorption of iodine, synthesis and secretion of thyroid hormones. PSNS fibers also approach the follicles and vessels of the thyroid gland. An increase in the tone of the PSNS (or the introduction of acetylcholine) is accompanied by an increase in the level of cGMP in thyrocytes and a decrease in the secretion of thyroid hormones.

Under the control of the central nervous system is the formation and secretion of TRH by small cell neurons of the hypothalamus, and, consequently, the secretion of TSH and thyroid hormones.

The level of thyroid hormones in tissue cells, their conversion into active forms and metabolites are regulated by the system of deiodinases - enzymes whose activity depends on the presence of selenocysteine ​​in cells and the intake of selenium into the body. There are three types of deiodinases (D1, D2, D3), which are distributed differently in different tissues of the body and determine the pathways for the conversion of thyroxine into active T 3, or inactive pT 3 and other metabolites.

Endocrine function of parafollicular K cells of the thyroid gland

These cells synthesize and secrete the hormone calcitonin.

Calcitonip (thyreocalcitoin)- a peptide consisting of 32 amino acid residues, the content in the blood is 5-28 pmol/l, acts on target cells, stimulating T-TMS membrane receptors and increasing the level of cAMP and IFZ in them. Can be synthesized in the thymus, lungs, central nervous system and other organs. The role of extrathyroidal calcitonin is unknown.

The physiological role of calcitonin is the regulation of calcium (Ca 2+) and phosphate (PO 3 4 -) levels in the blood. The function is implemented through several mechanisms:

• inhibition of the functional activity of osteoclasts and suppression of resorption bone tissue. This reduces the excretion of Ca 2+ and PO 3 4 - ions from bone tissue into the blood;
• reducing the reabsorption of Ca 2+ and PO 3 4 - ions from primary urine in the renal tubules.

Due to these effects, an increase in the level of calcitonin leads to a decrease in the content of Ca 2 and PO 3 4 - ions in the blood.

Regulation of calcitonin secretion is carried out with the direct participation of Ca 2 in the blood, the concentration of which is normally 2.25-2.75 mmol/l (9-11 mg%). An increase in calcium levels in the blood (hypsocalcismia) causes active secretion of calcitonin. A decrease in calcium levels leads to a decrease in hormone secretion. The secretion of calcitonin is stimulated by catecholamines, glucagon, gastrin and cholecystokinin.

An increase in calcitonin levels (50-5000 times higher than normal) is observed in one of the forms of thyroid cancer (medullary carcinoma), which develops from parafollicular cells. At the same time, the determination of high levels of calcitonin in the blood is one of the markers of this disease.

An increase in the level of calcitonin in the blood, as well as an almost complete absence of calcitonin after removal of the thyroid gland, may not be accompanied by a violation of calcium metabolism and condition skeletal system. These clinical observations indicate that physiological role The role of calcitonin in the regulation of calcium levels remains incompletely understood.

The function of the thyroid gland in the human body depends on many factors and is extremely important, as it participates in the regulation of most processes, is responsible for normal physical and mental development. The normal functioning of the thyroid gland depends not only on the hormones produced by it, but also on other external and internal factors. In case of deviations from normal level a variety of hormones develop pathological conditions, leading to disruption of the functioning of the entire organism.

In this article we will talk about anatomical structure the thyroid gland, the hormones it secretes, as well as diseases that can arise from pathologies of thyroid function in the human body.

The thyroid gland belongs to the endocrine glands, it is located on the front surface of the neck, at the level of 5-7 cervical vertebrae, in front of the larynx and trachea. The weight of the gland in an adult is approximately 30-40 g, but in women it is slightly larger, and during menstruation it can slightly change in size.

During puberty, the thyroid gland grows rapidly and by the age of 19-22 its weight increases 20 times. In many diseases, the size of the gland increases so much that it can be easily palpated with your own hands.

The gland is represented by two parts - left and right, connected to each other by means of an isthmus. The pyramidal part extends upward from the isthmus or from one of the lobes.

The thyroid gland is covered with a fibrous capsule, from which trabeculae extend, dividing it into parts. These parts are represented by multiple sacs - follicles, whose walls are inside lined with epithelial follicular cells, which have a cubic shape. Inside, the follicles are filled with a viscous mass - a colloid containing hormones.

Functions performed

We all have more or less an idea of ​​what kind of organ the thyroid gland is - the functions in the body of this part of the body are related to the production of hormones. The thyroid gland produces hormones such as triiodothyronine and calcitonin.

Thyroxine (T4) and triiodothyronine (T3) are formed only if there is a sufficient amount of iodine in the body. Iodine enters the body from food, water and the environment.

An extremely sensitive organ to the effects unfavorable factors is the thyroid gland - its structure and functions under conditions normal operation depend on the influence of hormones:

1. The hormone thyroxine includes 4 iodine atoms, does not have any particular activity, but affects many processes in the body, including ensuring growth, mental and physical development, stimulating energy metabolism, protein synthesis, catabolism of fats and carbohydrates.
2. What function does the thyroid gland perform using triiodothyronine? This hormone, like T4, contains iodine, but only 3 atoms. T3 is responsible for heart rate, regulates heat exchange in the body, reduces the concentration of cholesterol in the blood, stimulates the production of vitamin A, normalizes the metabolic process, and also affects physical growth and development and the normal functioning of the nervous system.
3. Calcitonin - unlike previous hormones, is not iodine-dependent; it is a peptide hormone consisting of 32 amino acids. It regulates the metabolism of phosphorus and calcium, maintaining them at the required level and preventing the destruction of bone tissue. Note! Calcitonin is a tumor marker for thyroid cancer, and when its levels rise, it indicates a serious pathology.

As we can see, the thyroid gland, thanks to the hormones it produces, is responsible for the normal development of the brain, central and autonomic nervous system, and also increases the activity of the sympathetic nervous system, increasing excitability, emotionality, heart rate, respiratory rate, sweating and reducing gastrointestinal motility.

Main diseases of the thyroid gland and methods of their diagnosis

By frequency endocrine pathologies thyroid lesions are in second place. As we know, one of the most sensitive organs - the thyroid gland - functions and disease are directly related. When the thyroid function increases or decreases, various pathologies, entailing serious consequences.

The most common of them are:

1. - a pathology in which the functionality of the gland increases. Symptoms that accompany this state caused by the influence of excessive amounts of thyroid hormones. Basically, the disease causes exophthalmos, tremor, tachycardia, increased nervous excitability, increased heat production, and weight loss.
2. Hypothyroidism– a condition in which the functional activity of the thyroid gland decreases. This disease causes lethargy, apathy, weight gain, swelling, decreased hearing and vision.
3. – an autoimmune disease accompanied by impaired functionality of the thyroid gland and an increase in its size. It is noteworthy that with this pathology signs of both hyperthyroidism and hypothyroidism can be observed.
4. Goiter– an increase in the size of the gland, which can occur in a nodular, diffuse or diffuse-nodular form. Goiter may also be accompanied by normal or increased level hormone, hypothyroidism is much less common with goiter.

It goes without saying that diseases do not appear out of nowhere. There are a lot of factors, often not directly related to the thyroid gland, but influencing it.

These factors include:

• existing chronic infectious diseases;
• autoimmune pathologies;
• frequent viral and bacterial diseases;
• bad habits;
• unfavorable environmental conditions;
• overdose of hormone replacement therapy drugs;
• exposure to toxic substances;
• thyroiditis;
• benign and malignant neoplasms of the thyroid gland or pituitary gland;
• tissue immunity to thyroid hormones;
• iodine deficiency;
• congenital absence or underdevelopment of the gland;
• conditions after partial or complete removal thyroid glands;
• therapy with radioactive iodine preparations;
• brain injuries.

Diagnostics

In order to determine whether the function of the thyroid gland is impaired, there are instructions that endocrinologists follow. In most cases, with impaired functionality, patients have a characteristic appearance.

However, to be absolutely sure, prescribe ultrasonography thyroid gland, as well as blood tests for triiodothyronine, thyroxine and pituitary thyroid-stimulating hormone. The price of these methods is not too high, and therefore endocrinological studies are very accessible to all segments of the population.

From the photos and videos in this article we learned about the functions of the thyroid gland, its structure and pathologies that arise when pathological processes in this body.