Because the basis of all the phenomena of life are the most complicated chemical and physico-chemical processes, it is quite natural that different chemical substances produced in the body, can have an impact on the functions of the bodies to which they fall through the blood or lymph.
With such phenomena we have already met, for example, when we were talking about regulating the secretion of gastric juice and pancreatic juice; describing the stomach, we noted that the contraction and relaxation of the pyloric sphincter is managed by the action of hydrochloric acid; considering the act of breathing, we talked about the effect of carbon dioxide on the activity of the respiratory center.
In the tissues of the body, actively functioning, and also at action of damaging factors, a special substance - histamine, which, even in small concentrations (millionths mg per 1 l) causes the expansion of capillaries. You probably saw red skin from burns, mechanical irritation or from a sting of insects; this reaction occurs under the influence of histamine. Believe that its effect is important for the regulation of local blood circulation, allowing the flow of blood in the time of work of the authority. Similar on action compounds adenosine - formed in muscles. Such examples are many. Mutual agreement of the functions of organs by means of chemical substances formed in the process of their activity, is a phenomenon that is very widespread in any organism. However, in a complex organism such mutual influence of bodies performing various functions, it would be quite inadequate to ensure its integrity, shared his reactions to changes continuously in the external and internal environment of the body. Therefore, in the process of evolution formed a special system of bodies, specialized on developing a very active chemical agents, which regulate certain vital processes that affect the metabolism and activity of separate bodies. These bodies have called endocrine glands, called also the endocrine, or endocrine, glands.
The glands carry out biochemical regulation. They do not have ducts and unlike all other glands secrete their juices - the so-called hormones, or incretions, directly into the blood or lymph. Exerting a powerful influence on various aspects of life of the organism, the glands are involved in the centralized management of its functions. In Fig. 43 presents the scheme of endocrine glands. You see that these small, but important organs are found in all parts of the body (excluding extremities). In the skull are the pituitary and pineal glands, which are simultaneously part of the brain. In the neck area lies the largest (adult) thyroid and next - smallest - parathyroid glands (called also epithelial cells); in the chest cavity is goiter, or thymus, and iron; in the abdominal cavity are pancreas, with the Islands of endocrine glandular tissue, and adrenal glands; in the pelvis (women) are the ovaries; in the scrotum (men) - testicles.
|Fig. 39. Diagram of the locations of the endocrine glands.
1 - pituitary or lower cerebral appendage;
2 - epiphysis - top cerebral appendage, or pineal gland;
3 - the thyroid gland;
4 - the thymus gland;
5 - adrenal;
6 - pancreas;
7 - ovary - female sex gland;
8 - testicle - male sex gland.
Small size of most of the endocrine glands were partly the reason that their discovery occurred mainly in the second half of the XIX and XX century, the First information about these glands we must not so much anatomical research, many clinical observations and experiments on animals. Every disease is a kind of experiment of nature. Opening of endocrine functions has been closely connected with the study of diseases of the endocrine glands. Afflicted by cancer in some cases enhance its function, in others, on the contrary, reduce it. Studying the consequences of violating the bodies that we understand their importance for normal body function.
The study of the properties of hormones showed that the chemical nature of their very different; some hormones have a relatively simple structure, such as thyroxine (thyroid gland), others, on the contrary, form a complex protein structures. That is, for example, insulin pancreas. Many of the hormones has not been studied. It is quite remarkable that hormones do not have the species specificity: they are identical in various species of animals and are found even in plants (for example, a male sex hormone can be obtained from the male flowers of palm earrings. This amazing fact is, undoubtedly, testifies to the deep unity of biological phenomena underlying the life of all organisms, as if greatly neither they differed from each other!
All the glands of internal secretion functionally closely connected; they are often compared with the artist of the same orchestra. The conductor of the ensemble is the lower cerebral appendage - pituitary and obviously not by chance, as it is closely associated with the Central nervous system, under the Supreme governance of which all the activities of the endocrine system.
Perhaps, before the others began to study in detail the sex glands, as they were more accessible to observation. In these glands Mature sex cells, which is the development of new individuals and maintenance of biological species. The products of the male sex glands - sperm - have been known for a very long time - since the opening of the microscope. The existence of mammals female reproductive cells, like eggs of birds was expected by Harvey, who owns dictum "Omne vivum ex ovo" - "All the living out of the egg; but first egg cell (i.e female reproductive cell) was found in the ovaries mammals only in the twenties of the last century Russian academician bear. However, only at the end of the last century it became clear that the sex glands produce, in addition to these cells, hormones, providing an extremely important effect on the structure and activities of the body. But in the current century has been studied their chemical composition and made possible their artificial fabrication. It turned out that there are several types of male sex hormones (for example, Androsterone, testosterone and other) and female sex hormones (for example, follikulina, astral and others). By their chemical nature they are very close.
Under the influence of sex hormones is the development of secondary sexual characteristics (the forming of the body and hair growth in male or female type, identifies structural features of the larynx and the corresponding features of male or female voice, and so on). The action of these hormones is determined by the desire of the sexes and was based on the peculiarities of the psyche of men and women. Female sex hormones, also regulate the cyclic changes in the genital area, associated with preparation of the body for pregnancy at each allocation egg cells (every three to four weeks) and control all those complex processes that occur in a woman's body during pregnancy.
Delete sex glands (castration) leads to the development of the phenomena of evnuhoidizm, i.e. to the formation of an individual of a certain medium type, deprived of the most important of sex differences. It has long been known. Such mutilation is subjected servants in harems, then became a reliable guardians wives; leaders of the Roman Catholic Church castrated boys - participants of the children's choir at the Vatican, to maintain their beautiful voices. The emasculation use in agricultural practices and in everyday life of your Pets.
The possession of drugs hormones sexual glands allow to achieve reliable therapeutic effect on many disorders of the functions of the sexual sphere, as well as in the treatment of certain tumors.
* Hormone therapy in some cases successfully used for the treatment of climacteric conditions, some form of sexual weakness, to regulate the process of pregnancy and childbirth.