Thyroid gland: functions and diseases
How the thyroid gland works, what functions it performs and why you can't consume too much iodine
Olga Smirnova, Post-science
Often, if a person, especially a woman, complains of poor health, malaise, lethargy and lack of energy, he is offered to check the thyroid gland. This is due to the fact that such symptoms may indicate an insufficiency of the thyroid gland. This disease is called hypothyroidism. No one knows why women have thyroid problems much more often than men. Most likely, this is due to the activity of female sex hormones. But the exact mechanisms of these processes are still unknown to us.
All vertebrates have a thyroid gland in one form or another, although not all have it framed in a gland. In the course of evolution, the functions and structure of the thyroid gland have changed somewhat in different species. For example, in frogs, thyroid hormone stimulates the transformation of a tadpole into a frog, that is, it is responsible for the differentiation of various parts of the body, as a result of which the tadpole becomes a frog. In mammals, the functions of the thyroid gland primarily affect the development of the brain in the initial period of embryo maturation, and in adulthood – its work. From the lower vertebrates to the higher functions were modified, but not radically.
In general, the study of the thyroid gland began to be engaged in at the end of the XIX century. This was due to observations indicating that residents of mountainous areas who drank water that did not contain iodine had a shortage of it, as a result of which the number of people suffering from cretinism increased. Cretinism is a disease associated with the fact that during embryogenesis, during intrauterine development, thyroid hormone was not synthesized, due to this, the brain developed poorly. This was especially noticeable in the Alpine areas, in Switzerland and neighboring areas. And since cretinism is a serious disease, it was actively studied and thus discovered that for the normal functioning of the thyroid gland, iodine must be supplied to the body along with food.
The structure and work of the thyroid gland
The thyroid gland consists of follicles – these are, as it were, such bubbles in which synthesized thyroid hormone accumulates in a protein-bound state. When it is necessary for more of these hormones to enter the bloodstream, part of the fluid that is inside the follicles and includes thyroid hormones (this fluid is called a colloid) is captured by the cells of the follicle shell, the protein is destroyed, and the hormone enters the blood. If the thyroid gland works too intensively, then such follicles become excessive, they produce more hormones. And if the thyroid gland does not work enough, then the follicles swell, become large, there is a lot of colloid inside them, because there are few hormones produced and few of them enter the blood.
Both with hyperthyroidism and hypothyroidism, goiter often occurs – an increase in the size of the thyroid gland, which is visible to the naked eye. But the reasons for this goiter are different: in case of insufficiency, this is due to the fact that the follicles are filled with colloid and there is a visible growth of the thyroid gland, and in hyperthyroidism this occurs due to a large number of small follicles, in which there is little colloid. There is also the concept of thyroid nodes – this is just a large number of follicles. They can be diffuse, that is, located throughout the thyroid gland, or, conversely, in such groups, clusters.
Functions of the thyroid gland
The thyroid gland is not only responsible for the production of a number of hormones, but is also regulated by them, and also has a direct, very serious effect on various types of tissues. If during pregnancy the fetus or already a newborn child had problems with the functions of the thyroid gland, not enough iodine was produced, then this can greatly affect mental abilities, up to cretinism. In adults, thyroid hormone affects energy exchange and the nervous system. If the thyroid gland produces an overabundance of hormones, then overexcitability occurs, and if, on the contrary, there are few of them, then a person suffers from lethargy and apathy.
The work of the thyroid gland depends on whether iodine enters our body. It is needed because the thyroid hormone contains iodine atoms, which we should receive together with food. Both excess and lack of iodine are equally harmful, so there should be certain norms of its consumption. In Russia, they used to be somehow regulated by the state, but now this does not happen, so quite often there are diseases associated not only with insufficiency, but also with an overabundance of iodine. We often see ads for drugs containing iodine, people take them because they think it's useful. But in fact, this is a double-edged sword.
Thyroid diseases
Among the most common diseases of the thyroid gland, hyperthyroidism and hypothyroidism associated with an overabundance or lack of thyroid hormones should be mentioned first of all. Hyperthyroidism produces too many thyroid hormones, which causes a number of characteristic symptoms. Most of all, exophthalmos is known, that is, bug-eyed, as well as trembling of the hands and increased heartbeat. Others are excessive arousal, insomnia, hyperactivity, irritability, weight loss. If you take too much iodine, these symptoms may just appear.
There are many reasons that can lead to thyroid diseases. For example, the same hyperthyroidism may be associated with the appearance of antibodies that mimic the action of a hormone that stimulates the functions of the thyroid gland – thyroid-stimulating hormone. That is, because of this, the thyroid gland does not work under the influence of the pituitary gland - it just has a thyroid–stimulating hormone, which is responsible for stimulating the thyroid gland – but under the influence of antibodies very similar to it.
The main diseases of the thyroid gland in adulthood (with the exception of cretinism that occurs in utero) they are autoimmune in nature. By the way, the female immune system is more prone to such diseases than the male one. Hyperthyroidism and hypothyroidism are associated with the production of antibodies to various thyroid proteins, and therefore the thyroid gland suffers more often in women, since autoimmune processes occur more often in them. That is, the cause of pathologies is not in the direct effect of female sex hormones on the thyroid gland, but in their effect on the immune system: due to this, it works more intensively, antibodies to its own proteins are produced, including thyroid proteins. These antibodies can cause both hypofunction and hyperfunction of the thyroid gland. In addition, the causes of thyroid diseases may be genetic mutations. They can occur in adulthood in individual cells, but they can also be hereditary, although this is a fairly rare option.
There are many such reasons, but they have the same result: a violation of the thyroid gland. To find out for sure, it is necessary to do a number of analyses. And the treatment of the disease largely depends on the causes. Cancer is also found among thyroid diseases, but, as a rule, this is a fairly favorable current disease. Most often it is not cancer of cells that produce thyroid hormones, but cancer of cells that produce another hormone – calcitonin. This is the most common form of thyroid cancer, but any thyroid cancer is quite easy to treat, and in most cases people live quite a long time or recover. So thyroid cancer is not particularly dangerous compared to other types of cancer.
Treatment and research of thyroid diseases
Regarding the treatment of most thyroid diseases, everything has been known for a long time. Hypothyroidism is treated with the introduction of hormones, that is, taking pills. It all depends on the right dose. The patient needs to be taught to listen to his feelings, how insufficiently excitable or hyperexcited he is. If the dose of the drug is too large, then symptoms of hyperthyroidism will appear, and if insufficient, then hypothyroidism will persist.
Hyperthyroidism is treated both medically and surgically. But the fact is that after the removal of thyroid nodes that produce a large amount of hormones, insufficiency occurs. This is not always due to the fact that a large area of the thyroid gland is removed. In recent years, it has become clear that this may be due to the fact that the proteins that are in the follicles enter the blood during surgery, and the immune system, which is not familiar with these proteins, begins to produce antibodies to them. That is, the operation itself can provoke the process of an autoimmune attack on the thyroid gland and cause hypothyroidism. Due to these data, surgical treatment is now used much less frequently, other methods that reduce thyroid function are used together with it.
Symptoms of thyroid disorders
There are quite a lot of symptoms that could signal problems with the thyroid gland. But the trouble is that they can also relate to other diseases, so without tests it is impossible to say for sure whether health problems are the result of insufficiency or hyperfunction of the thyroid gland. With hyperfunction, a characteristic feature is tremor (trembling of the hands), tachycardia (heartbeat disorder). Women have special triggers for the occurrence of thyroid diseases, for example pregnancy or stress, leading to hyperthyroidism, as a result of which the above signs arise.
Hypothyroidism mainly manifests itself in lethargy and apathy. The worse the thyroid gland works, the greater this lethargy. As a result, patients are reluctant to even go to doctors. Mental activity decreases, drowsiness appears, weight increases. But, as mentioned above, this does not necessarily indicate problems with the thyroid gland, there are other diseases with similar symptoms, and without tests it is impossible to say anything for sure. Therefore, hypothyroidism is more difficult to diagnose, whereas the symptoms of hyperthyroidism – tachycardia and tremor – are quite definite. But even in some cases, people with such symptoms go first to cardiologists, who can sometimes begin to treat the heart, whereas the root cause is not in it, but in the thyroid gland. With hypothyroidism, on the contrary, the heartbeat is reduced and the pressure decreases, which also leads to weakness.
About the author:
Olga Smirnova – Doctor of Biological Sciences, Professor of the Department of Human and Animal Physiology, Head of the Laboratory of Endocrinology of the Faculty of Biology of Lomonosov Moscow State University.
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26.07.2017