Classification of hormones. The role of hormones in the human body

Hormones are chemical constituents of an integral system of regulation of body functions. They are substances of different nature, capable of transmitting signals to cells. The result of these interactions is a change in the direction and intensity of metabolism, growth and development of the body, the launch of important functions or their inhibition and correction.

A hormone is an organic chemical substance, the synthesis of which takes place in the endocrine glands or in the endocrine glands of mixed secretion. They are released directly into the internal environment, through which they spread and are chaotically transferred to the target organs. Here they are able to exert a biological effect, which is realized through receptors. Because each hormone has an exceptional specificity for a specific receptor. This means that these substances affect one function or process in the body. Classification of hormones by action, tropism to the tissues and the chemical structure, this shows more clearly.

The general idea of the importance of hormones

Modern classification of hormones considers these substances from a variety of points of view. And they are united in one: only organic substances are called hormones, the synthesis of which proceeds only in the body. Their presence is characteristic of virtually all vertebrates, in which the regulation of body functions also represents the combined work of humoral and nervous systems. And in the phylogeny, the humoral regulatory system appeared earlier than the nervous one. Even in primitive animals, it was available, although it was responsible for the most basic functions.

Hormones and biologically active substances

It is believed that the very system of biological active substances (BAS) and receptors specific to them is characteristic even of the cell. However, the concepts of "hormone" and "BAS" are not identical. The hormone is called BAS, which is secreted into the internal environment of the body and exerts an effect on a distant group of cells. BAS, in turn, affects locally. Examples of BAS, also called hormone-like substances, are Ceylons. These substances are released by a population of cells, where they inhibit multiplication and regulate apoptosis. Examples of BAS are also prostaglandins. Modern classification of hormones allocates for them a special group of eicosanoids. They are designed for local regulation of inflammation in tissues and for hemostasis processes at the level of arterioles.

Chemical classification of hormones

Hormones are divided into several groups according to the chemical structure. This divides them and the mechanism of action, because these substances have different indicators of tropism to water and lipids. So, the chemical classification of hormones looks like this:

• Peptide group (excreted by pituitary, hypothalamus, pancreatic and parathyroid glands) ;
• Steroid group (allocated endocrine parts of the male sex glands and cortical areas of the adrenal glands);
• Group of amino acid derivatives (formed by the thyroid gland and adrenal medulla);
• Group of eicosanoids (excreted by cells, synthesized from arachidonic acid).

It is noteworthy that the sex hormones of women are also included in the steroid group. However, steroids, by and large, are not: the effect of hormones of this type is not associated with an anabolic effect. At the same time, their metabolism does not lead to the formation of 17-ketosteroids. Hormones of the ovaries, though structurally similar to other steroids, are not such. Since they are synthesized from cholesterol, to simplify the basic chemical classifications, they are ranked among the remaining steroids.

Classification by synthesis site

Hormonal substances can be divided and the place of synthesis. Some are formed in peripheral tissues, while others are formed in the central nervous system. On this depends the way of secretion and secretion of substances, which determines the features of the realization of their effects. The classification of hormones in place is as follows:

• Hypothalamic hormones (releasing factors);
• Pituitary (tropic hormones, vasopressin and oxytocin);
• Thyroid (calcitonin, tetraiodothyronine and triiodothyronine);
• Parathyroid (parathyroid hormone);
• Non-adrenal (norepinephrine, adrenaline, aldosterone, cortisol, androgens);
• Sexual (estrogens, androgens);
• Pancreatic (glucagon, insulin);
• Tissue (leukotrienes, prostaglandins);
• Hormones APUD (motilin, gastrin and others).

The last group of hormonal substances is not fully understood. It is synthesized in the largest group of endocrine glands located in the upper intestine, in the liver and pancreas. Their goal is to regulate the secretion of exocrine digestive glands and intestinal motility.

Classification of hormones by the type of effect

Various hormonal substances have a different effect in biological tissues. They are divided into the following groups:

• Metabolism regulators (glucagon, triiodothyronine, tetraiodothyronine, cortisol, insulin);
• Regulators of the functions of other endocrine glands (releasing factors of the hypothalamus, tropic hormones of the pituitary gland);
• Regulators of calcium and phosphorus metabolism (parathyroid hormone, calcitonin and calcitriol);
• Regulators of water-salt balance (vasopressin, aldosterone);
• Regulators of reproductive function (sex hormones);
• Stress hormones (norepinephrine, adrenaline, cortisol);
• Regulators of limits and growth rates, cell division (somatotropin, insulin, tetraiodothyronine);
• Regulators of central nervous system functions , limbic system (cortisol, adrenocorticotropic hormone, testosterone).

Secretion and transportation of hormones

The secretion of hormones occurs immediately after their synthesis. They fall directly into the blood or into the tissue fluid. The last place of secretion is characteristic for eicosanoids: they do not have to act far from the cell, because they regulate the functions of the whole tissue population. And the hormones of the ovaries, pituitary gland, pancreas and others should be carried with blood through the body in search of target organs having receptors specific for them. From the blood they enter the intercellular fluid, where they go to the cell of the target organ.

Signaling to the receptor

The above classification of hormones reflects the effects of the action of substances on tissues and organs. Although this is possible only after binding the chemical to the receptor. The latter are different and are located both on the cell surface, and in the cytoplasm, on the nuclear membrane and inside the nucleus. Because of the way the signal is transmitted, substances are divided into two types:

• Extracellular transfer mechanism;
• Intracellular signaling.

This basic classification of hormones allows us to draw conclusions about the speed of signal transmission. For example, the extracellular mechanism is much faster than the intracellular one. It is typical for adrenaline, norepinephrine and other peptide hormones. The intracellular mechanism is characteristic of lipophilic steroids. Moreover, the benefit for the body is achieved faster when synthesizing precisely the peptides. After all, the production of steroid hormones is much slower, and their mechanism of signal transmission is also slowed down by the need for protein synthesis and maturation.

Characteristics of the types of signal transmission

The extracellular mechanism is characteristic of peptide hormones, which can not enter the cytoplasmic membrane into the cytoplasm without a specific carrier protein. This is not for him, and the signal itself is transmitted through the adenylate cyclase system by changing the conformation of the receptor complexes.

The intracellular mechanism is much simpler. It is carried out after the penetration of the lipophilic substance into the cell, where it meets the cytoplasmic receptor. With it, it forms a hormone-receptor complex, which penetrates the nucleus and affects specific genes. Their activation leads to the initiation of protein synthesis, which is the molecular effect of this hormone. The actual effect is already a protein that regulates the given function after its synthesis and formation.