Hormones are substances that are synthesized in the human body with the help of specialized endocrine glands. Each hormone has a specific biological activity. At the moment, there are approximately 60 substances that are secreted by the glands and have hormonal activity.
Main types of hormones
The most widespread classification of hormones depending on their chemical structure. They are divided into the following types:
- protein hormones that can be simple or complex;
- biologically active substances of peptide nature: calcitonin, oxytocin, somatostatin, glucagon, vasopressin;
- amino acid derivatives: thyroxine, adrenaline;
- biologically active substances of lipid nature: corticosteroids, female and male sex hormones;
- tissue hormones: heparin, gastrin.
As noted above, protein hormones are further divided into two subspecies:
- simple: insulin, growth hormone, prolactin;
- complex: lutropin, follicle-stimulatinghormone, thyroid-stimulating hormone.
Examples of protein hormones and their functions should be considered depending on the organ in which they are synthesized. And these can be the following structures of the body:
- pituitary gland;
- parathyroid glands;
- cells of the gastrointestinal tract.
Biologically active substances of the hypothalamus
Absolutely all the substances that are produced by the hypothalamus belong to the group of hormones-proteins and polypeptides. Their main function is to regulate the production of hormones in the pituitary gland. Depending on how they perform this function, there are several varieties:
- releasing hormones increase pituitary activity;
- statins inhibit the synthesis of biologically active substances by the pituitary gland;
- Hormones in the posterior lobe do not affect the activity of the pituitary gland, accumulate in its posterior part before being released into the blood.
The hypothalamus indirectly through the pituitary gland affects the function of the thyroid gland and adrenal glands, the reproductive system, and regulates human growth.
Releasing hormones include the following substances:
- somatotropin releasing hormone (SHR);
- thyrotropin releasing hormone (TRH);
- gonadotropin releasing hormone (GnRH);
- corticotropin releasing hormone (CRH).
The function of hormone proteins of this group is to increase the synthesis of the correspondingbiologically active substances in the pituitary gland. So, SRG stimulates the production of somatotropic hormone and prolactin, TRH enhances the production of thyroid-stimulating hormone, GnRH increases the synthesis of luteinizing and follicle-stimulating hormones, CRH increases the production of corticotropin. Moreover, all tropic hormones are formed in the anterior pituitary gland (there are three in total).
KRG has not only biological, but also neuronal activity. Therefore, it is also referred to the class of neuropeptides. Due to the transmission of CRH in nerve synapses, a person experiences feelings of anxiety, fear, anxiety, sleep and appetite disorders, and a decrease in sexual activity. With prolonged exposure to corticotropin-releasing hormone, persistent mental disorders develop: depression, anxiety, insomnia, exhaustion of the body.
TRH also belong to the class of neuropeptides. He is involved in the implementation of certain mental functions. For example, its antidepressant activity has been established.
GnRH synthesis has a certain cyclicity. It is produced for several minutes every 1-3 hours.
Biologically active substances of the pituitary gland
Protein hormones are also substances that are synthesized in the anterior and posterior lobes of the pituitary gland. Moreover, tropic hormones are produced in the anterior region, while the formation of new substances does not occur in the posterior region, but oxytocin and vasopressin accumulate, which were previously synthesized in the hypothalamus.
Tropical structures include the following peptide and protein structures:
- adrenocorticotropic hormone (ACTH);
- thyroid stimulating hormone (TSH);
- luteinizing hormone (LH);
- follicle stimulating hormone (FSH).
They all have a stimulating effect on the peripheral endocrine glands. Thus, ACTH increases the activity of the adrenal glands, TSH activates the thyroid gland, and LH and FSH activate the gonads.
Effector biologically active substances are isolated separately. They do not regulate the function of the endocrine glands, but stimulate organs that are outside the endocrine system.
Adrenocorticotropic hormone is directly connected with the adrenal glands, namely with its cortex. It increases the synthesis and release of corticosteroids into the bloodstream. It is characteristic that only two layers of the adrenal cortex are stimulated - the bundle and the reticular cortex. The glomerular zone, where mineralocorticoids are synthesized, is not under the influence of tropic biologically active substances of the pituitary gland.
The size of ACTH is small. It consists of only 39 amino acid residues. Its concentration in the blood, compared with other hormones, is not very high. The synthesis of this substance has a clear dependence on the time of day. This is called the circadian rhythm. Its maximum amount in the blood is observed in the morning when the body wakes up. This is due to the need to mobilize all the forces of the body after sleep. Also, the amount of these protein hormones increases in stressful situations.
In addition to the effect of ACTH on the adrenal cortex, it also acts on structures that are not related toendocrine system. So, it increases the breakdown of lipids in adipose tissue.
With an increase in the activity of the adrenal glands, for example, in Itsenko-Cushing's syndrome, the production of ACTH decreases according to the feedback mechanism. This, in turn, inhibits the synthesis of corticotropin-releasing hormone in the hypothalamus.
Thyroid stimulating hormone, or TSH, has two parts: alpha and beta. The alpha part of TSH is similar to that of gonadotropic hormones, and the beta part is unique to thyrotropin. TSH regulates the growth of the thyroid gland, ensuring its increase in size. This substance also increases the synthesis of thyroxine and triiodothyronine, the main thyroid hormones that are necessary for normal metabolism in the body.
Releasing hormones of the hypothalamus affect the production of TSH in the pituitary gland. The feedback mechanism also works here: with increased activity of the thyroid gland (thyrotoxicosis), TSH synthesis in the pituitary gland is inhibited, and vice versa.
Gonadotropic hormones (GnTG) in mammals, including humans, are represented by follicle-stimulating (FSH) and luteinizing (LH) hormones. They differ not only in their structure, but also in function. Moreover, they are somewhat different depending on the gender. In women, FSH stimulates the growth and maturation of follicles; in men, it is needed for the formation of spermatic cords and differentiation of spermatozoa.
LH in girls is involved in the formation of the corpus luteum in the ovaries, ovulation. In men, these protein hormones perform the functionsecretion of testosterone by the testes. Moreover, testosterone is produced not only in men, but also in women.
Answering the question of which protein hormones stimulate the production of FSH and LH hormones in the pituitary gland, it is worth noting that this is only one hormone. It is called gonadotropin-releasing hormone. In addition to the activity of the peripheral endocrine glands, the synthesis of GnRH is regulated by the organs of the central nervous system (the limbic part of the brain).
Effective hormones of the anterior pituitary gland
Effective protein hormones perform the function of stimulating the activity of internal organs that are outside the endocrine system. These include:
- somatotropic hormone;
- melanocyte-stimulating hormone.
Somatotropic hormone or growth hormone is a large protein that includes 191 amino acid residues. Its structure is very similar to the structure of another pituitary hormone - prolactin.
The main function of somatotropin is to stimulate the growth of bones and the whole organism. The growth process under the influence of somatotropin is carried out by increasing the size and number of cells that are in the cartilage of the epiphyses (extreme parts of the bones). After puberty is over, cartilage is replaced by bone. As a result, somatotropin can no longer stimulate bone growth. Therefore, a person grows up to a certain age.
Excessive synthesis of growth hormone in childhood leads tothat the child grows too tall. But all parts of the body are enlarged proportionally. This condition is called gigantism. If somatotropin is actively produced in adults, there is a disproportionate growth of individual parts of the body - acromegaly.
If, on the contrary, somatotropic growth hormone was produced in insufficient quantities, dwarfism develops. The child grows very short, but the proportions of the body are preserved.
Biologically active substances of the pancreas
The pancreas belongs to the group of glands of mixed secretion. This means that in addition to the synthesis of hormones, it also produces enzymes that are necessary for the digestion of food in the intestines. The synthesis of protein hormones and enzymes are the two most important functions of the pancreas.
The most important biologically active substances that are produced in the pancreas are insulin and glucagon. They are antagonists to each other, that is, they perform absolutely opposite functions. Due to the coordinated action of these hormones, normal carbohydrate metabolism is ensured.
Insulin is formed in the islets of Langerhans from proinsulin. It reduces the concentration of glucose in the blood through the following processes:
- increasing its utilization in cells;
- inhibition of gluconeogenesis (glucose synthesis in the liver);
- inhibition of glycolysis (the breakdown of glycogen to glucose);
- stimulate glycogenesis (formation of glycogen from glucose).
Insulin also promotes the formation of proteins and fats. That is, herefers to anabolic hormones. Glucagon has exactly the opposite effect, and therefore it was classified as a catabolic hormone.
Hormones-proteins and lipids are very important substances in the body. Proteins, which are synthesized mainly in the hypothalamus and pituitary gland, affect the synthesis of biologically active substances in the peripheral endocrine glands. And steroid and sex hormones, which are produced in the adrenal glands and gonads under the action of proteins, are vital for humans.
The production of biologically active substances throughout the body occurs smoothly, under strict control. And violation of these functions can lead to dangerous and sometimes irreversible consequences.