As a hormone system , cells secreting various signal substances and incretory glands are combined to form an organ system that regulates various metabolic processes and organ functions in the body of a multicellular organism via hormones . Hormones are messenger substances that have a paracrine effect on neighboring cells in the vicinity or reach their target cells after they have been released into the bloodstream endocrinically .
The endocrine system ( ancient Greek ἔνδον endon , German 'inside' ; ancient Greek κρίνειν krinein , German 'separate, secrete' ) includes not only the various endocrine glands ( glands without ducts) and endocrine cells scattered in the heart, kidneys, liver, lungs and gastrointestinal tract (especially small intestine), thymus and brain. There are also paracrine cells that release tissue hormones .
Hormones exert only an effect as an extracellular signaling substances when in the cell membrane or cytosol specific a cell hormone receptors are present, proceeding from which the signal in each cell-type effects converted is.
Endocrinology is a medical field of concern for diseases of the endocrine system or endocrinopathies .
The endocrine glands include:
- Pituitary gland ( hypophysis or glandula pituitaria )
- Pineal gland ( epiphysis cerebri , epiphysis , glandula pinealis )
- Thyroid gland ( glandula thyroidea )
- Parathyroid gland (epithelial bodies, parathyroid gland )
- Adrenal gland ( glandula adrenalis or glandula suprarenalis )
- Langerhans Islands (island organ, Insulae pancreaticae )
Endocrine cells include the Leydig intermediate cells in the testes and the theca and granulosa cells of the ovarian follicle or the corpus luteum in the ovary , as well as those heart muscle cells that release the atrial natriuretic peptide . Both the adrenal medulla and paraganglia occupy an intermediate position between the endocrine and neural systems . The endocrine system is closely linked to the nervous system, which is why both are also summarized as the neuroendocrine system . As a circumventricular organ, the pineal gland is also part of the nervous system.
In addition, there are endocrine cells in almost all epithelia , which are collectively referred to as the diffuse neuroendocrine system (DNES) or APUD . These cells in the gastrointestinal tract , also referred to here as the gastro-entero-pancreatic endocrine system (GEP), have so far been researched best . The majority of these cells, however, have a paracrine effect, although endocrine drug transfer has been proven for some.
Within the endocrine system, groups of endocrine organs are linked by communication networks. As a result, their current function is coordinated and an appropriate performance in the overall system is guaranteed. Typical structures of these interactions are control loops , environment inhibitions and antagonistic subsystems, with which control variables are often safely set several times.
The hypothalamus, a small area in the diencephalon , connects this to the hormonal system. It has contact with the pituitary gland ( pituitary gland ) via a portal vein system and regulates its hormone secretion. Most of the information exchange takes place via this system through hormones that are formed in the nerve cells ( neurons ) of the hypothalamus. It regulates the body temperature, the heartbeat and the kidney function, but also hunger and thirst as well as our sleep rhythm and the sex drive.
The diencephalon lies between the cerebellum and the cerebrum. From here the autonomic nervous system is controlled, which is responsible for the energy, heat and water balance of our body, among other things.
The superordinate gland within the endocrine system is the pea-sized pituitary gland, which lies in a bony depression in the middle cranial fossa and controls most of the endocrine system . It is the center of the endocrine system and the other endocrine organs. Besides the production of its own hormones, it also influences the hormone production of the other endocrine glands. The pituitary gland consists of two halves that work independently: the posterior pituitary lobe (neurohypophysis) and the anterior pituitary gland (adenohypophysis).
The posterior pituitary lobe is connected directly to the hypothalamus via the pituitary stalk. Historically a part of the hypothalamus (i.e. the brain), it stores hormones that are formed there and transported to it via the common nerve connection.
The anterior pituitary lobe is directly connected to the hypothalamus. Various hormones are produced in the anterior lobe that act directly on body tissues and other glands. They are controlled by factors that form in the hypothalamus and reach the anterior lobe via a special vessel. In addition, the anterior lobe reacts independently to high levels of hormones in the blood. For example, when the thyroid hormone level is sufficiently high, the production of the hormone that stimulates the thyroid gland is stopped.
These hormones are responsible for the cells' energy turnover and for protein production. In order for the thyroid to produce it, it needs iodine , which it receives and stores from the blood. If the energy turnover is faster or slower than normal, one speaks of an overactive thyroid or an underactive thyroid . Increased values can cause nervousness, weight loss and emotional tension, while in the other extreme case the body functions run more slowly.
The four small parathyroid glands are on the back of the thyroid gland. Your hormone (the parathyroid hormone ) has the function of regulating the body's calcium balance.
The body needs calcium for building bones and teeth, for the function of nerve and muscle cells and for blood clotting. Together with vitamin D , which is formed in the skin under the influence of light, the hormone of the parathyroid glands enables calcium to be absorbed from food.
When the body does not get enough calcium, the hormone causes calcium to be released from the bones into the blood.
The pancreas, located behind the stomach in the upper abdomen, is the only gland made up of an endocrine and an exocrine part ; it is basically two organs in one. The endocrine part - the islets of Langerhans - produces insulin and glucagon and in this way regulates the blood sugar level, while an enzyme-containing digestive juice comes from the larger exocrine system, which is conducted into the duodenum via special passages .
The adrenal glands can be distinguished into the adrenal medulla and the adrenal cortex. The inner adrenal medulla produces the hormones adrenaline and noradrenaline . In dangerous or stressful situations, adrenaline is released from the adrenal medulla into the bloodstream. This increases the heart rate and the blood vessels in the skin and intestines constrict; hence the saying: He got cold feet. The blood is available to the working muscles and the blood pressure rises. At the same time, the sugar stored in the liver and muscles is broken down into simple sugars so that the body has more energy available.
The adrenal cortex produces three types of steroid hormones with different functions: Aldosterone reduces the excretion of salt through the kidneys and thus increases the water content of the body. The release of aldosterone is controlled by the renin produced in the kidney . If the aldosterone level is too low, the kidneys produce more renin.
When the body needs more energy, cortisol increases blood sugar levels. It converts protein into sugar, working together with the hormones adrenaline and glucagon, which also increase blood sugar levels. A high cortisol level reduces the body's defense against infection.
The sex glands are created in pairs, in women as almond-shaped ovaries in the pelvic area of the abdominal cavity, in men as egg-shaped testicles in the scrotum. Both men and women produce the sex hormones estrogen , progesterone , testosterone and androsterone . However, due to their different proportions, the effect on women is different from that on men.
The male sexual characteristics - for example beard growth and deep voice - are characterized by a preponderance of testosterone and androsterone. On the other hand, estrogen and progesterone are responsible for the female sexual characteristics - for example the development of the breasts and the widening of the hips.
- Lois Jovanovic, Genell J. Subak-Sharpe: Hormones. The medical manual for women. (Original edition: Hormones. The Woman's Answerbook. Atheneum, New York 1987) From the American by Margaret Auer, Kabel, Hamburg 1989, ISBN 3-8225-0100-X .
- Paul Honekamp: About the disorders of the endocrine-vegetative system, their causes and their healing through natural healing substances. Carl Marhold, Halle 1935.