Endocrine system

• It takes part in the humoral (chemical) regulation of body functions and coordinates the activities of all organs and systems.
• Provides preservation of homeostasis of the body under changing environmental conditions.
• Together with the nervous and immune systems, it regulates:
  • growth;
  • body development;
  • its sexual differentiation and reproductive function;
  • takes part in the processes of education, use and conservation of energy.
• In conjunction with the nervous system, hormones are involved in providing:
  • emotional reactions;
  • human mental activity .

It is represented by endocrine glands that synthesize, accumulate and release various biologically active substances (hormones, neurotransmitters, and others) into the bloodstream. Classical endocrine glands: pineal gland , pituitary , thyroid , parathyroid glands , islet apparatus of the pancreas , adrenal cortex and medulla , testes , ovaries are referred to the glandular endocrine system. In the glandular system, endocrine cells are concentrated within a single gland. The central nervous system is involved in the regulation of the secretion of hormones of all endocrine glands, and hormones by the feedback mechanism affect the central nervous system , modulating its activity and condition. Nervous regulation of the activity of the peripheral endocrine functions of the body is carried out not only through the tropic hormones of the pituitary gland (pituitary and hypothalamic hormones), but also through the influence of the autonomous (or autonomic ) nervous system. In addition, a certain amount of biologically active substances (monoamines and peptide hormones ) are secreted in the central nervous system itself, many of which are also secreted by the endocrine cells of the gastrointestinal tract ^[1] . The endocrine glands (endocrine glands) are organs that produce specific substances and secrete them directly into the blood or lymph. These substances are hormones - chemical regulators necessary for life. The endocrine glands can be both independent organs and derivatives of epithelial (borderline) tissues.

Hypothalamic-pituitary system

The hypothalamus and pituitary gland have secretory cells, while the hypothalamus is considered an element of the important " hypothalamic-pituitary system ."

In the hypothalamus, the hypothalamic proper ( vasopressin or antidiuretic hormone , oxytocin , neurotensin ) and biologically active substances that inhibit or enhance the secretory function of the pituitary gland ( somatostatin , thyroliberin or thyreotropin-releasing hormone, luliberin or gonadoliberin - cordinbormin -liberate, or gonadoliberin - cordin-liberin, or gonadoliberin - cordin-liberin, or gonadoliberin - cordin-liberin, or secreted hormone and somatoliberin or somatotropin-releasing hormone) ^[1] . One of the most important glands of the body is the pituitary gland , which controls the work of most of the endocrine glands . The pituitary gland is small, weighing less than one gram, but very important for the life of iron. It is located in a recess at the base of the skull , connected with the hypothalamic region of the brain by the leg and consists of three lobes - the anterior ( glandular , or adenohypophysis ), middle or intermediate (it is less developed than others) and the posterior ( neurohypophysis ). By the importance of the functions performed in the body, the pituitary can be compared with the role of the conductor of the orchestra, which shows when a particular instrument should come into play. Hypothalamic hormones (vasopressin, oxytocin, neurotensin) flow down the pituitary leg into the posterior lobe of the pituitary gland , where they are deposited and, if necessary, are released into the bloodstream. The pituitary hormones of the hypothalamus, released into the portal pituitary system, reach the cells of the anterior pituitary gland, directly affecting their secretory activity, inhibiting or stimulating the secretion of tropic pituitary hormones, which, in turn, stimulate the work of peripheral glands of internal secretion ^[1] .

The anterior pituitary gland is the most important organ for regulating the basic functions of the body: it is here that the six most important tropic hormones are produced that regulate the secretory activity of peripheral endocrine glands - thyroid stimulating hormone (TSH), adrenocorticotropic hormone ( ACTH ), somatotropic hormone (STH or growth hormone ), lactotropic hormone ( prolactin ) and two gonadotropic hormones that regulate the functions of peripheral genital glands : follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Thyrotropin accelerates or slows down the thyroid gland , ACTH regulates the adrenal cortex , somatotropin (growth hormone) indirectly (through somatomedins or insulin-like growth factors ) controls the growth and development of the bone system , cartilage and muscles . Excessive production of growth hormone in an adult leads to the development of acromegaly , which is manifested by an increase in bone thickness, overgrowth of cartilage (nose, auricles) and bones of the facial skull. The pituitary gland is closely associated with the hypothalamus, with which it is the connecting link between the brain , peripheral nervous system and circulatory system . The connection between the pituitary and hypothalamus is carried out using various chemicals that are produced in the so-called neurosecretory cells.

The posterior pituitary gland does not produce its own hormones, its role in the body is the accumulation and secretion of two important hormones produced by the neurosecretory cells of the hypothalamic nuclei: antidiuretic hormone (ADH), which is involved in the regulation of the body's water balance, increasing the degree of fluid re-absorption in the kidneys and oxytocin , which is responsible for the contraction of smooth muscles and, in particular, the uterus during childbirth.

Thyroid

The thyroid gland ( lat. Glandula thyr (e) oidea ) is an endocrine gland in vertebrates that stores iodine and produces iodine-containing hormones (iodothyronines) that are involved in the regulation of metabolism and growth of individual cells, as well as the body as a whole - thyroxine (tetraiodothyronine, T ₄ ) and triiodothyronine (T ₃ ). The thyroid gland, whose weight ranges from 20 to 30 g, is located in the front of the neck and consists of two lobes and an isthmus located at the level of ΙΙ — ΙV cartilage of the trachea (respiratory throat) and connects both lobes. Four parathyroid glands are located in pairs on the back surface of two lobes. Outside, the thyroid gland is covered with neck muscles located below the hyoid bone; its fascial bag of iron is firmly connected to the trachea and larynx, so it moves after the movements of these organs. The gland consists of follicles - oval or round bubbles, which are filled with a protein iodine-containing substance such as a colloid; between the bubbles is loose connective tissue. Bubble colloid is produced by the epithelium and contains hormones produced by the thyroid gland - thyroxine (T ₄ ) and triiodothyronine (T ₃ ).

Another hormone secreted by parafollicular or C-cells of the thyroid gland - calcitonin (a polypeptide by its chemical nature) regulates the content of calcium and phosphates in the body, and also prevents the formation of osteoclasts , which in the activated state can lead to the destruction of bone tissue, and stimulates functional activity and reproduction of osteoblasts . Thus, it is involved in the regulation of the activity of these two types of formations, it is thanks to the hormone that new bone tissue forms faster. The action of this hormone is directly opposite to parathyroidin , which is produced by the parathyroid gland and increases the level of calcium in the blood, enhances its influx from the bones and intestines. From this point of view, the action of parathyroidin resembles vitamin D.

Parathyroids

The parathyroid gland regulates the level of calcium in the body within a narrow framework so that the nervous and motor systems function normally. When blood calcium levels fall below a certain level, calcium-sensitive parathyroid receptors activate and secrete the hormone into the blood. Parathyroid hormone stimulates osteoclasts to release calcium from bone tissue into the blood.

Pancreas

The pancreas is a large (12-30 cm long) secretory organ of double action (secreting pancreatic juice into the lumen of the duodenum and hormones directly into the bloodstream), located in the upper abdominal cavity , between the spleen and duodenum.

The endocrine pancreas is represented by islets of Langerhans located in the tail of the pancreas. In humans, islets are represented by various types of cells that produce several polypeptide hormones:

• alpha cells - secrete glucagon (a regulator of carbohydrate metabolism, a direct insulin antagonist );
• beta cells - secrete insulin (a regulator of carbohydrate metabolism, lowers blood glucose );
• delta cells - secrete somatostatin (inhibits the secretion of many glands);
• PP-cells - secrete pancreatic polypeptide (inhibits the secretion of the pancreas and stimulates the secretion of gastric juice);
• Epsilon cells - secrete ghrelin (“hunger hormone” - stimulates appetite ).

Adrenal glands

At the upper poles of both kidneys are small glands of a pyramidal shape - the adrenal glands. They consist of the outer cortical layer (80–90% of the mass of the entire gland) and the inner medulla, the cells of which lie in groups and are braided by wide venous sinuses. The hormonal activity of both parts of the adrenal glands is different. The adrenal cortex produces mineralocorticoids and glycocorticoids with a steroid structure. Mineralocorticoids (the most important of them is aldosterone ) regulate ion exchange in cells and maintain their electrolytic balance; glycocorticoids (e.g. cortisol ) stimulate protein breakdown and carbohydrate synthesis. The brain substance produces adrenaline - a hormone from the catecholamine group, which supports the tone of the sympathetic nervous system. Adrenaline is often called the hormone of struggle or flight, since its release increases sharply only in minutes of danger. An increase in the level of adrenaline in the blood entails the corresponding physiological changes - the heart rate quickens, the blood vessels narrow, the muscles tighten, the pupils dilate. Another cortical substance in small quantities produces male sex hormones (androgens). If abnormalities occur in the body and androgens begin to flow in extreme quantities, the signs of the opposite sex increase in girls. The cortex and medulla of the adrenal glands differ not only in the production of different hormones. The work of the adrenal cortex is activated by the central and the medulla by the peripheral nervous system.

Gonads

The maturation and sexual activity of a person would be impossible without the work of the gonads, or genital glands, which include the male testes and female ovaries . In young children, sex hormones are produced in small quantities, but as the body grows up at a certain point, a rapid increase in the level of sex hormones occurs, and then male hormones (androgens) and female hormones (estrogens) cause a person to have secondary sexual characteristics.

Epiphysis

The function of the pineal gland is not fully understood. The pineal gland secretes substances of a hormonal nature, serotonin, which in them also turns into melatonin, an antigonadotropin that weakens the secretion of lutropin in the anterior pituitary gland. Along with antigonadotropin, pinealocytes form another protein hormone that increases the level of potassium in the blood. Of the regulatory peptides, arginine-vasotocin, thyroliberin, and luliberin are the most important.

Thymus

The immune system, including the thymus gland (thymus) produces a large number of hormones, which can be divided into cytokines or lymphokines and thymic (or thymic) hormones - thymopoietins that regulate the growth, maturation and differentiation of T cells and the functional activity of mature immune cells system . The cytokines secreted by immunocompetent cells include: gamma- interferon , interleukins (1–7 and 9–12), tumor necrosis factor, granulocyte colony stimulating factor, granulocytomacrophage colony stimulating factor, macrophage colony stimulating factor, leukemic inhibitor factor and others ^[1] . With age, the thymus degrades, being replaced by a connective tissue formation.

В диффузной эндокринной системе эндокринные клетки не сконцентрированы, а рассеяны.

Некоторые эндокринные функции выполняют печень (секреция соматомедина, инсулиноподобных факторов роста и др.), почки (секреция эритропоэтина, медуллинов и др.), желудок (секреция гастрина), кишечник (секреция вазоактивного интестинального пептида и др.), селезёнка (секреция спленинов) и др. Эндокринные клетки содержатся во всём организме человека.

Выделено и описано более 30 гормонов, которые секретируются в кровяное русло клетками или скоплениями клеток, расположенными в тканях желудочно-кишечного тракта . Эндокринные клетки желудочно-кишечного тракта синтезируют гастрин , гастринсвязывающий пептид , секретин , холецистокинин , соматостатин , вазоактивный интестинальный полипептид (ВИП), вещество P , мотилин , галанин , пептиды гена глюкагона ( глицентин , оксинтомодулин , глюкагоноподобный пептид 1 и 2), нейротензин, нейромедин N , пептид YY , панкреатический полипептид , нейропептид Y , хромогранины (хромогранин A и относящиеся к нему пептид GAWK и секретогранин II).

• Эндокринный контроль можно рассматривать как цепь регуляторных эффектов, в которой результат действия гормона прямо или косвенно влияет на элемент, определяющий содержание доступного гормона.
• The interaction occurs, as a rule, according to the principle of negative feedback : when the hormone acts on the target cells, their response, affecting the source of hormone secretion, causes a suppression of secretion.
  • Positive feedback, in which secretion is enhanced, is extremely rare.
• The endocrine system is also regulated through the nervous and immune systems.

Endocrine diseases are a class of diseases that arise as a result of a disorder of one or more endocrine glands. Endocrine diseases are based on hyperfunction, hypofunction, or dysfunction of endocrine glands.

Apudoms

Apudomas are tumors originating from cellular elements located in various organs and tissues (mainly islet (incretory) cells of the pancreas, cells of other sections of the gastrointestinal tract, C cells of the thyroid gland) that produce polypeptide hormones. Currently described the following types of apoud ^[2] :

• VIPoma ;
• Gastrinoma
• Glucagonoma ;
• Carcinoid;
• Neurotensinoma;
• PPoma ;
• Somatostatin

Vipoma Syndrome

VIPoma (Werner-Morrison syndrome, pancreatic cholera, water diarrhea-hypokalemia-achlorhydria syndrome) - is characterized by the presence of water diarrhea and hypokalemia as a result of islet cell hyperplasia or a tumor, often malignant, coming from the islet cells of the pancreas (usually the body and tail), which secrete a vasoactive intestinal polypeptide (VIP). In rare cases, VIP can occur in ganglioneuroblastomas, which are localized in the retroperitoneal space, lungs, liver, small intestine and adrenal glands, are found in childhood and, as a rule, are benign. The size of pancreatic VIPs is 1 ... 6 cm. In 60% of cases of malignant neoplasms at the time of diagnosis there are metastases ^[3] . The incidence of VIPoma is very small (1 case per year per 10 million people) or 2% of all endocrine tumors of the gastrointestinal tract . In half the cases, the tumor is malignant. The prognosis is often unfavorable.

Gastrinoma

With G-cell hyperplasia , a gastrinoma is formed - a benign or malignant tumor localized in the pancreas, duodenum or jejunum, or even in the peripancreatic lymph nodes , in the gates of the spleen or in the wall of the stomach. This tumor produces a greater amount of gastrin, hypergastrinemia occurs, which, through the mechanism of stimulation of parietal cells, causes excessive production of hydrochloric acid and pepsin . In a normal situation, G cells under the influence of hydrochloric acid inhibit the production of gastrin, but the acid factor does not affect gastrin G cells. As a result, multiple peptic ulcers of the stomach, duodenum or jejunum develop. Gastrin secretion by gastrinomas is particularly dramatically enhanced after eating.

The clinical manifestation of hypergastrinemia is Zollinger – Ellison syndrome (type 1) ^[4] .

Glucagonoma

Glucagonoma is a tumor, often malignant , originating from the alpha cells of pancreatic islets . It is characterized by migratory erosive dermatosis, angular apapacheylitis, stomatitis, glossitis, hyperglycemia, normochromic anemia. It grows slowly, metastasizes to the liver. There is 1 case per 20 million aged 48 to 70 years, more often in women ^[2] .

A carcinoid is a malignant tumor that usually occurs in the gastrointestinal tract, which produces several substances that have a hormone-like effect.

Neurotensinoma

Ppoma

PPoma is a pancreatic tumor secreting pancreatic polypeptide (PP). Clinical manifestations are practically absent. More often diagnosed after metastasis to the liver ^[2] . Treatment: surgical, chemotherapy and symptomatic. The prognosis depends on the start date of treatment.

Somatostatinoma

Somatostatinoma is a slowly growing malignant tumor characterized by an increase in somatostatin. This is a rare disease that occurs in people over 45 years of age - 1 case per 40 million ^[2] .

Distinguish:

• somatostatin from pancreatic delta cells and
• apomatoma secreting somatostatin - a tumor of the duodenum .

Diagnosis based on the clinic and increased levels of somatostatin in the blood. Surgical treatment, chemotherapy and symptomatic. The prognosis depends on the timeliness of treatment.

• Hormones
• Exocrine glands
• gland

• The doctrine of the organs of internal secretion - Endocrinology