The thyroid gland is an unpaired endocrinological organ. Only vertebrates have it. Thyroid hormones and their functions play a significant role: they regulate metabolism, exchange of calcium, phosphate and, together with the nervous system, control all processes in the body.

How the thyroid gland works

The medical name for the thyroid gland is the thyroid gland. It is located next to the trachea – between the collar zone and the Adam’s apple. Looks like a butterfly or a horseshoe. On average, it weighs 30-60 grams. These values ​​depend on the height, weight and age of the person, nutrition, and medication. When hormones accumulate, its size can vary. So, in women during menstruation or pregnancy, the thyroid gland increases.  

The thyroid gland consists of:

• right lobe,
• left lobe,
• isthmus,
• pyramidal lobe.

The isthmus connects both parts of the organ in the middle and is located on the anterior wall of the trachea. The pyramidal lobe is present only in every third person. It is a remnant of the organ on the basis of which the thyroid gland developed in the course of evolution.

Due to the connection with the larynx, the thyroid gland is mobile. She moves when swallowing or tilting her head. The thyroid gland is more actively supplied with blood than other organs – in terms of the level of blood flow, even the brain is inferior to it. And its role is so important that already at birth it is fully formed, unlike other organs.

The thyroid gland consists of follicles – small rounded vesicles. They are filled with a cell-free liquid substance – a colloid. On the edge of the follicles, thyrocytes are adjacent. It is they who produce iodinated hormones. Then they accumulate in the colloid, and from there enter the blood. 

Larger parafollicular C-cells are located between colloids . They produce the hormone thyrocalcitonin. It regulates calcium-phosphate metabolism: inhibits the removal of calcium from the bones, reduces its amount in the blood, as well as intestinal and kidney absorption. 

What hormones does the thyroid gland produce?

The thyroid gland synthesizes two types of hormones:

1. iodized,
2. thyrocalcitonin.

Iodinated include triiodothyronine and thyroxine. The first consists of 4 iodine molecules, and the second – of 4. Therefore, they are designated T3 and T4, respectively. 

The synthesis of hormones is impossible if iodine does not enter the body. That is why the daily consumption of iodine-containing foods is important. The amino acid tyrosine is also involved in the formation of T4 and T3. She also comes with food. In addition, with its help adrenaline, dopamine and melanin are synthesized.

Calcitonin is closely related to calcium levels in the body. If the element is sufficient, the production of the hormone decreases and vice versa.

Regulation process

Once in the blood, thyroid hormones combine with transport proteins. If this did not happen, the elements would be “washed out” by the kidneys due to their small size. This process also regulates their level – they are inactive when bound. In tissues, T4 is converted to T3. 90% of the biological action of the elements occurs due to triiodothyronine.

The synthesis of thyroxine and triiodothyronine consists of several stages:

1. Iodine enters the body from foods and is absorbed in the intestines.
2. Iodine is transported and absorbed in the thyroid cells.
3. There is a synthesis of thyroglobulin – a protein that precedes the formation of hormones.
4. The thyroid gland absorbs thyroglobulin from the colloid and breaks down its molecules into thyroxine and triiodothyronine.
5. Hormones are released into the bloodstream.

The process of production of T3 and T4 by the thyroid gland is regulated by the hypothalamus and pituitary gland. They are found in the brain. The first “monitors” the level of thyroid hormones and, if they are lacking, produces thyrotropin-releasing hormone (TRH). 

TRH affects the pituitary gland. When a substance enters the cerebral appendage, it produces TSH, a thyroid stimulating hormone that regulates the function of the thyroid gland. The latter, together with the blood, enters the thyroid gland and stimulates the synthesis of T4 and T3.

The interaction of the hypothalamus, pituitary and thyroid gland is built on a negative cascade principle. When hormone levels drop, areas of the brain stimulate their production. If it rises, they inhibit the production of T4 and T3.

Functions

The thyroid gland affects all tissues of the body. Normal work of any organ is impossible without it. Once in the cell, T3 enters the nucleus. Here it connects with specific areas of chromosomes and stimulates oxidation and reduction processes.

The main functions of thyroid hormones:

1. Participate in the formation of red blood cells.
2. Stimulates the production of protein required for the formation of new cells and tissue growth. Congenital hormone deficiency leads to dwarfism.
3. Affect the development of the genitals.
4. Enhances the breakdown of fat cells.
5. They stimulate the processes of absorption in the intestine, the synthesis of glucose and an increase in its level in the blood.
6. Influence the formation of the central nervous system. In children with a lack of thyroid hormones, a decrease in intelligence is observed and cretinism (lag in the development of the brain) develops.
7. Control metabolic processes, heat and sweat production.
8. Affects reflexes and behavioral factors.

Diseases associated with a lack or excess of hormones 

There are three conditions associated with thyroid hormones:

1. euthyroidism – hormones are normal;
2. hypothyroidism – lack of T3 and T4;
3. hyperthyroidism – increased content of thyroxine and triiodothyronine.

Hypothyroidism provokes an insufficient amount of iodine and the intake of certain medications (“Cordaron”). Also, the disease develops when the thyroid gland is removed and thyroid-stimulating hormone deficiency. In a child, hypothyroidism leads to disproportionate growth, developmental delay, cretinism. In adults, an endemic goiter is formed.

The main symptoms of hypothyroidism are:

1. weight gain, regardless of diet and physical activity;
2. tiredness and increased weakness;
3. depressed psycho-emotional state;
4. malfunctions of the ovaries: menstrual irregularities, infertility;
5. low temperature: 35.6-36.3 ° C;
6. dry skin, itching, dandruff, leg swelling, hair loss, split nails;
7. regular constipation;
8. low blood pressure and heart rate;
9. constant feeling of cold;
10.                    muscle and joint pain;
11.                    decreased memory and reactions;
12.                    anemia – a decrease in hemoglobin levels.

Hyperthyroidism develops due to increased production of T4 and T3. It appears with diffuse toxic goiter, viral de Quervain’s thyroiditis, nodular toxic goiter, Hashimoto’s autoimmune thyroiditis. The reasons for its development also include taking medications (“Thyroxin”, “Eutirox”), tumors of the pituitary gland, ovaries, iodine overdose, thyroid cancer.

External manifestations of hyperthyroidism include:

1. swelling of the eyes;
2. weight loss with high appetite;
3. emotional instability, overexcitement, irritability;
4. disruptions in the menstrual cycle, infertility;
5. increased body temperature: 36.9–37.5 ° C;
6. dry skin;
7. high blood pressure and heart palpitations;
8. decreased ability to perceive and remember information;
9. constant feeling of heat even in cool rooms;
10.                    regular diarrhea.

Diagnostics

Thyroid hormone levels are measured by blood sampling. Their number is determined by two methods: radioimmunoassay and enzyme immunoassay. In addition, an ultrasound scan is performed. It will show the size of the gland, its volume, if any, nodes and cysts.