Hormones may be
The endocrine system coordinates the communication between different organs by hormones, which are chemicals that are released from certain cells within endocrine (Seamlessly) glands in the bloodstream. Once released into the bloodstream, hormones affect the function of the target tissue, which may be another endocrine gland or end organ .. Some hormones cells influence exactly the organ from which they were also distributed (paracrine effect), some even affect the same cell type (autocrine effect). Hormones may be peptides of varying sizes steroids (derived from cholesterol) amino acid derivatives hormones bind selectively to receptors on the inside or on the surface of target cells. Hormones interact with intracellular receptors that regulate gene function (eg. As corticosteroids, vitamin D and thyroid hormones). Receptors on the cell surface bind hormones that control enzyme activity or influence ion channels (eg., Growth hormones, thyrotropin-releasing hormone). Endocrine diseases resulting from disorders of the endocrine glands and / or the target tissue. The pituitary and its target organs. Relationship between the hypothalamus and pituitary function peripheral endocrine organs is regulated to varying degrees by the pituitary hormones. Some functions (for. Example, the secretion of insulin from the pancreas, which is primarily controlled by blood glucose levels) are controlled pituitary only to a minimum level while other functions mainly (for. Example, the secretion of thyroid hormones or sex hormones) are regulated by the pituitary gland. The secretion of pituitary hormones is controlled by the hypothalamus. The interaction between the hypothalamus and pituitary gland (hypothalamo-pituitary-loop) is a feedback system. The hypothalamus receives information from virtually all other areas of the CNS and passes it on to the pituitary gland. As a result, the pituitary gland releases several hormones that stimulate the endocrine glands throughout the body. Changes in the concentration of circulating hormones are recognized by the hypothalamus, which then increases its stimulating effects on the pituitary or decreased to maintain homeostasis. The hypothalamus modulated in different ways the activity of the anterior and posterior pituitary. Neurohormones that are synthesized in the hypothalamus reach the anterior pituitary (adenohypophysis) via special portal vessels and regulate synthesis and release of the six major peptide hormones of the anterior pituitary (the pituitary and its target organs.). regulate the hormones of the anterior pituitary glands, both peripheral endocrine (thyroid, adrenal cortex and the gonads) as well as growth and lactation. Between the hypothalamus and anterior pituitary there is no direct neural connection. In contrast, the posterior pituitary (neurohypophysis) contains axons of neuronal cells in the hypothalamus. These axons serve as storage for two peptide hormones from the hypothalamus, vasopressin (antidiuretic hormone) and oxytocin), which control the homeostasis of water balance, the milk ejection and uterine contractions in the periphery. Phases of hormone release are interrupted by periods of inactivity. Almost all hormones produced in the hypothalamus and pituitary are given in pulsatile form. Some hormones (eg. As adrenocorticotropic hormone [ACTH], growth hormone, prolactin) have fixed circadian rhythms, other hormones (eg. As luteinizing hormone and follicle-stimulating hormone during the menstrual cycle) in addition to the circadian rhythm have a monthly periodicity. Hypothalamic neurohormones neurohormones Affected anterior pituitary effect corticotropin-releasing hormone ACTH stimulation dopamine prolactin LH FSH TSH inhibition inhibition inhibition inhibition gonadotropin-releasing hormone LH FSH stimulation * Stimulation * Growth hormone-releasing hormone GH stimulation prolactin-releasing hormone Prolactin stimulation somatostatin GH TSH inhibition inhibition thyrotropin-releasing hormone TSH stimulation Prolactin stimulation * Under Physiologic pean conditions and intermittent doses. Continuous application inhibits the release of LH and FSH. ACTH = adrenocorticotropic hormone (corticotropin); FSH = follicle stimulating hormone; GH = growth hormone (growth hormone); LH = luteinizing hormone; TSH = thyroid-stimulating hormone. Hypothalamic control far, seven were physiologically important neurohormones of the hypothalamus are identified (see table: hypothalamic neurohormones). In addition to the biogenic amine dopamine are all of the above hormones small peptides. Some are produced both in the periphery and in the hypothalamus and act in local paracrine systems, especially in the GI tract. An example of this is the vasoactive intestinal peptide (VIP), which stimulates the release of prolactin. Neurohormones can control the release of various hormones of the pituitary gland. The distribution of most of the anterior pituitary hormones is dependent on stimulatory signals from the hypothalamus. An exception is prolactin, which is regulated by an inhibitory signal. In the case of severance of the webs pituitary (which is the pituitary gland with the hypothalamus connect) the prolactin release is increased while the release of all other hormones of the anterior pituitary decreases. A variety of changes in the hypothalamus (z. B. tumors or encephalitis, and other inflammatory processes) can affect the release of neurohormones. Since neurohormones are synthesized in different regions within the hypothalamus, some changes in the hypothalamus affect only a single neuropeptide, while other lesions change a variety of hormones. The result can be both a neurohormonal overactive and an underactive. Clinical syndromes of pituitary hormones from pathological release result (z. B. diabetes insipidus, acromegaly and hypopituitarism). are diseases of the pituitary gland. The cells of the anterior pituitary functions of the anterior pituitary (which represent 80% of the weight of the pituitary gland) synthesize and secrete stimulating hormones which are necessary for normal growth and development and the activity of various target glands. Adrenocorticotropic hormone (ACTH) ACTH is also called corticotropin. Corticotropin releasing hormone (CRH) is the main stimulator of ACTH release. Under stress and vasopressin plays a role. ACTH causes the adrenal cortex to release cortisol and several weak androgens such. B. dehydroepiandrosterone (DHEA). Circulating cortisol and other corticosteroids (including exogenous corticosteroids) inhibit the release of CRH and ACTH. The axis CRH-ACTH cortisol is a key component of the physiological stress response. Without ACTH it comes to atrophy of the adrenal cortex, and the cortisol dried nahezu.Thyreoidea-stimulating hormone (TSH) TSH regulates thyroid function, because it stimulates the synthesis and release of thyroid hormone. The synthesis and release of TSH pituitary is stimulated by thyrotropin-releasing hormone (TRH), and by circulating thyroid hormone (negative feedback) inhibiert.Luteinisierendes hormone (LH) and follicle stimulating hormone (FSH) LH and FSH control the production of sex hormones. Synthesis and release of LH and FSH are mainly by gonadotropin releasing hormone (GnRH) stimulated and inhibited by estrogen or testosterone. One factor which controls the release of GnRH, is Kisspeptin that is triggered by increased leptin levels at puberty a hypothalamic peptide. Two gonadal hormones, activin and inhibin, affect only on FSH; Activin is stimulating and inhibin is inhibitory. In women, LH and FSH stimulate the development of follicles in the ovaries and ovulation. In men, FSH acts on the Sertoli cells and is essential for spermatogenesis. LH acts on Leydig cells in the testes and stimulates testosterone Biosynthese.Wachstumshormon (growth hormone, GH) GH stimulates physical growth and regulates the metabolism. Growth hormone-releasing hormone (GHRH) is the main stimulator, and somatostatin is the main inhibitor of the synthesis and release of GH. GH controls the synthesis of insulin-like growth factor 1 (IGF-1, also called somatomedin-C), which largely determines the growth. IGF-1 is produced in many tissues, however, the liver is the primary production site. A variant of IGF-1 is found in muscle tissue, where it plays a role in improving muscle strength. It is not so much under the control of GH as the liver variant. The metabolic effects of GH are biphasic. First, GH is insulin-like effects, such as increasing glucose uptake in muscle and fat cells, stimulation of amino acid uptake and protein synthesis in the liver and muscles as well as an inhibition of lipolysis in adipose tissue. A few hours later occur metabolic effects that are opposite to the action of insulin. This includes inhibition of glucose uptake and consumption, which in turn increases blood glucose levels and lipolysis, which leads to increased plasma concentration of free fatty acids. The concentration of GH levels rise during periods of starvation to maintain blood glucose levels and to mobilize fat as an alternate energy source. The production of GH decreases with age. Ghrelin, which is produced in the gastric fundus a hormone that supports the release of GH from the pituitary, increased food intake and improves the Gedächtnis.Prolactin Prolactin is produced in so-called lactotrophs cells, which represent about 30% of all cells of the pituitary gland. During pregnancy, the pituitary doubled its size, which is mainly due to hypertrophy and hyperplasia of lactotrophs cells. In humans, the main function of prolactin is to stimulate milk production. Also during sexual activity and stress it comes to prolactin secretion. Prolactin can be a sensitive indicator of pituitary dysfunction. Prolactin is a hormone that is formed in the case of a tumor of the pituitary most frequently excessive. Upon interruption of the vascular connection between the hypothalamus and pituitary occurs by eliminating the inhibitory effects of dopamine on the cells for lactotrophs Entzügelungshyperprolactinämie.Andere hormones Several other hormones are produced in the anterior pituitary. These include pro-opiomelanocortin (POMC, the prohormone of ACTH), alpha and beta melanocyte-stimulating hormone (MSH), beta-LPH (?-LPH), the enkephalins and endorphins. POMC and MSH can cause hyperpigmentation of the skin; they appear clinically only for faults in appearance, in which the ACTH secretion is markedly increased (for. example, Addison’s disease, Nelson-tumor). The function of the pituitary ?-LPH is not known. Enkephalins and endorphins are endogenous opioids that bind throughout the CNS to opioid receptors and activate them. Function of the pituitary The pituitary gland pours vasopressin (also arginine vasopressin or antidiuretic hormone [ADH] and oxytocin from. Both hormones in response to neural impulses released and have a half-life of about 10 minutes. Vasopressin (antidiuretic hormone, ADH) supports vasopressin primarily the renal conservation of water by increasing the permeability of the epithelium of the distal tubule and collecting ducts. at high concentrations, vasopressin also causes vasoconstriction. As aldosterone plays vasopressin a significant role in the maintenance of fluid homeostasis and the vascular and cellular hydration. the main stimulus for the release of vasopressin is an increase in the osmotic pressure of body water, which is recognized by osmoreceptors in the hypothalamus. another important Stimulus is a lack of volume, which is detected by baroreceptors in the left atrium into the pulmonary veins, in the carotid sinus and the aortic arch, and is then forwarded via the vagus nerve and the glossopharyngeal nerve in the CNS. Other stimulators of vasopressin secretion are pain, distress, vomiting, hypoxia, sports, hypoglycemia, cholinergic receptor agonists, ?-blockers, angiotensin and prostaglandins. lead alcohol, alpha-blockers and glucocorticoids to inhibit vasopressin release. A lack of vasopressin leads to a central insipidus diabetes. The inability of the kidney to an adequate response to vasopressin caused a insipidus renal diabetes. The removal of the pituitary gland usually do not lead to a permanent diabetes insipidus, since the remaining neurons of the hypothalamus are capable of producing vasopressin. Copeptin is produced together with vasopressin in the pituitary gland. Its measurement can in distinguishing the cause of a hyponatremia useful sein.Oxytocin Oxytocin has two main goals: The myoepithelial cells of the mammary which the alveoli of the mammary gland surrounding cells of the smooth muscle of the uterus sucking on the nipple stimulates the release of oxytocin, which is used for contraction of the myoepithelial cells leads. This contraction causes milk to flow from the alveoli into the large sinus, from where it is delivered (eg. As the milk ejection reflex nursing mothers). Oxytocin stimulates contraction of smooth muscle in the uterus. The sensitivity of the uterus to oxytocin increases during pregnancy. The oxytocin increase during labor not essential. The role of oxytocin in the induction of labor is unclear. In men, no stimulus for oxytocin is known, although very low levels of oxytocin are detectable here.