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endocrine system
Wikipedia
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In physiology, the endocrine system is a organ system|system of glands, each of which secretes a type of hormone into the bloodstream to regulate the body. The endocrine system is an information signal system like the nervous system. Hormones are substances (chemical mediators) released from endocrine tissue into the bloodstream that attach to target tissue and allow communication among cells. Hormones regulate many functions of an organism, including Mood (psychology)|mood, human development (biology)|growth and development, tissue (biology)|tissue function, and metabolism. The field of study that deals with disorders of endocrine glands is endocrinology, a branch of internal medicine.
The endocrine system is made up of a series of ductless glands that produce chemicals called hormones. A number of glands that signal each other in sequence is usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis.
Typical endocrine glands are the pituitary, thyroid, and adrenal glands. Features of endocrine glands are, in general, their ductless nature, their vascularity, and usually the presence of intracellular vacuoles or granules storing their hormones. In contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract, tend to be much less vascular and have ducts or a hollow Lumen (anatomy)|lumen.
In addition to the specialised endocrine organs mentioned above, many other organs that are part of other body systems, such as the kidney, liver, heart and gonads, have secondary endocrine functions. For example the kidney secretes endocrine hormones such as erythropoietin and renin.
Endocrine organs and secreted hormones
Hypothalamus| Abbreviation !! width=17% | Produced by !! Effect |
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Thyrotropin-releasing hormone
(Prolactin-releasing hormone) | TRH, TRF, or PRH || Paraventricular nucleus of hypothalamus|Parvocellular neurosecretory neurons || Stimulate Thyroid-stimulating hormone|thyroid-stimulating hormone (TSH) release from anterior pituitary (primarily)
Stimulate prolactin release from anterior pituitary |
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Dopamine
(Prolactin-inhibiting hormone) | DA or PIH || Arcuate nucleus|Dopamine neurons of the arcuate nucleus || Inhibit prolactin release from anterior pituitary |
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| Growth hormone-releasing hormone | GHRH || Neuroendocrine neurons of the Arcuate nucleus || Stimulate Growth hormone|Growth hormone (GH) release from anterior pituitary |
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Somatostatin
(growth hormone-inhibiting hormone) | SS, GHIH, or SRIF || Neuroendocrine cells of the Periventricular nucleus || Inhibit Growth hormone|Growth hormone (GH) release from anterior pituitary
Inhibit Thyroid-stimulating hormone|thyroid-stimulating hormone (TSH) release from anterior pituitary |
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| Gonadotropin-releasing hormone | GnRH or LHRH || Neuroendocrine cells of the Preoptic area || Stimulate Follicle-stimulating hormone|follicle-stimulating hormone (FSH) release from anterior pituitary
Stimulate Luteinizing hormone|luteinizing hormone (LH) release from anterior pituitary |
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| Corticotropin-releasing hormone | CRH or CRF || Paraventricular nucleus of hypothalamus|Parvocellular neurosecretory neurons || Stimulate Adrenocorticotropic hormone|adrenocorticotropic hormone (ACTH) release from anterior pituitary |
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| Oxytocin | || Magnocellular neurosecretory cells || Uterine contraction
Letdown reflex|Lactation (letdown reflex) |
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Vasopressin
(antidiuretic hormone) | ADH or AVP || Paraventricular nucleus of hypothalamus|Parvocellular neurosecretory neurons || Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume |
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Pineal body (epiphysis)| From cells !! Effect |
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| Melatonin | Antioxidant
Monitors the circadian rhythm including inducement of drowsiness and lowering of the core body temperature |
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Pituitary Gland (hypophysis)
=Anterior pituitary lobe (adenohypophysis)=| Abbreviation !! width=17% | From cells !! Effect |
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Growth hormone
(somatotropin) | GH || Somatotrophs || Stimulates human development (biology)|growth and cell (biology)|cell reproduction
Stimulates Insulin-like growth factor 1 release from liver |
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Thyroid-stimulating hormone
(thyrotropin) | TSH || Thyrotrophs || Stimulates thyroxine (T4) and triiodothyronine (T3) synthesis and release from thyroid gland
Stimulates iodine absorption by thyroid gland |
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Adrenocorticotropic hormone
(corticotropin) | ACTH || Corticotrophs || Stimulates corticosteroid (glucocorticoid and mineralcorticoid) and androgen synthesis and release from Adrenal cortex|adrenocortical cells |
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| Follicle-stimulating hormone | FSH || Gonadotrophs || In females: Stimulates maturation of ovarian follicles in ovary
In males: Stimulates maturation of seminiferous tubules
In males: Stimulates spermatogenesis
In males: Stimulates production of androgen-binding protein from Sertoli cells of the testes |
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| Luteinizing hormone | LH || Gonadotrophs || In females: Stimulates ovulation
In females: Stimulates formation of corpus luteum
In males: Stimulates testosterone synthesis from Leydig cell|Leydig cells (interstitial cells) |
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| Prolactin | PRL || Lactotrophs || Stimulates milk synthesis and release from mammary glands
Mediates orgasm|sexual gratification |
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=Posterior pituitary lobe (neurohypophysis)=| Abbreviation !! width=17% | From cells !! Effect |
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| Oxytocin | || Magnocellular neurosecretory cells || Uterine contraction
Letdown reflex|Lactation (letdown reflex) |
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Vasopressin
(antidiuretic hormone) | ADH or AVP || Paraventricular nucleus of hypothalamus|Parvocellular neurosecretory neurons || Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume |
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Oxytocin and anti-diuretic hormone are not secreted in the posterior lobe, merely stored.
=Pars intermedia|Intermediate pituitary lobe (pars intermedia)=| Abbreviation !! width=17% | From cells !! Effect |
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| Melanocyte-stimulating hormone | MSH || Melanotropes || Stimulates melanin synthesis and release from skin/hair melanocytes |
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Thyroid| Abbreviation !! width=17% | From cells !! Effect |
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| Triiodothyronine | T3 || Thyroid epithelial cell || (More potent form of thyroid hormone)
Stimulates body oxygen and energy consumption, thereby increasing the basal metabolic rate
Stimulates RNA polymerase I and II, thereby promoting protein synthesis |
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Thyroxine
(tetraiodothyronine) | T4 || Thyroid epithelial cell''s || (Less active form of thyroid hormone)
(Acts as a prohormone to triiodothyronine)
Stimulates body oxygen and energy consumption, thereby increasing the basal metabolic rate
Stimulates RNA polymerase I and II, thereby promoting protein synthesis |
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| Calcitonin | || Parafollicular cell''s || Stimulates osteoblasts and thus bone construction
Inhibits calcium|Ca2+ release from bone, thereby reducing blood Ca2+ |
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Alimentary system
Stomach| Abbreviation !! width=17% | From cells !! Effect |
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| Gastrin (Primarily) | || G cells || Secretion of gastric acid by parietal cells |
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| Ghrelin | || P/D1 cells || Stimulate appetite, | secretion of growth hormone from anterior pituitary gland |
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| Neuropeptide Y | NPY || || increased food intake and decreased physical activity |
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| Somatostatin | || Delta cell|D cells || Suppress release of gastrin, cholecystokinin (CCK), secretin, motilin, vasoactive intestinal peptide (VIP), gastric inhibitory polypeptide (GIP), enteroglucagon | Lowers rate of gastric emptying | Reduces smooth muscle contractions and blood flow within the intestine. | |
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| Histamine | || ECL cells || stimulate gastric acid secretion |
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| Endothelin | || X cells || Smooth muscle contraction of stomach |
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Duodenum| From cells !! Effect |
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| Secretin | Secretion of bicarbonate from liver, pancreas and duodenal Brunner's glands | Enhances effects of cholecystokinin | Stops production of gastric juice |
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| Cholecystokinin | Release of digestive enzymes from pancreas | Release of bile from gallbladder | hunger suppressant |
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Liver| Abbreviation !! width=17% | From cells !! Effect |
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| Insulin-like growth factor (or somatomedin) (Primarily) | IGF || Hepatocytes || insulin-like effects | regulate cell growth and development |
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| Angiotensinogen and angiotensin | || Hepatocytes || vasoconstriction | release of aldosterone from adrenal cortex | dipsogen. |
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| Thrombopoietin | || Hepatocytes || stimulates megakaryocytes to produce platelets |
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Pancreas| From cells !! Effect |
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| Insulin (Primarily) | Intake of glucose, glycogenesis and glycolysis in liver and muscle from blood | intake of lipids and synthesis of triglycerides in adipocytes | Other anabolism|anabolic effects |
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| Glucagon (Also Primarily) | glycogenolysis and gluconeogenesis in liver | increases blood glucose level |
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| Somatostatin | Inhibit release of insulin | Inhibit release of glucagon | Suppress the exocrine secretory action of pancreas. |
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| Pancreatic polypeptide | PP cells || Self regulate the pancreas secretion activities and effect the hepatic glycogen levels. |
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Kidney| From cells !! Effect |
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| Renin (Primarily) | Juxtaglomerular cells || Activates the renin-angiotensin system by producing angiotensin I of angiotensinogen |
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| Erythropoietin (EPO) | Extraglomerular mesangial cells || Stimulate erythrocyte production |
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| Calcitriol (1,25-dihydroxyvitamin D3) | || Active form of vitamin D3|vitamin D3 | Increase absorption of calcium and phosphate from gastrointestinal tract and kidneys | inhibit release of parathyroid hormone|PTH |
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| Thrombopoietin | || stimulates megakaryocytes to produce platelets |
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Adrenal glands
Adrenal cortex| From cells !! Effect |
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| Glucocorticoids (chiefly cortisol) | zona fasciculata and zona reticularis cells || Stimulates gluconeogenesis
Stimulates fat breakdown in adipose tissue
Inhibits protein synthesis
Inhibits glucose uptake in muscle and adipose tissue
Inhibits immunological responses (immunosuppressive)
Inhibits inflammatory responses (anti-inflammatory) |
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| Mineralocorticoids (chiefly aldosterone) | Zona glomerulosa cells || Stimulates active sodium reabsorption in kidneys
Stimulates passive water reabsorption in kidneys, thus increasing blood volume and blood pressure
Stimulates potassium and Hydrogen ion|H+ secretion into nephron of kidney and subsequent excretion |
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| Androgens (including dehydroepiandrosterone|DHEA and testosterone) | Zona fasciculata and Zona reticularis cells || In males: Relatively small effect compared to androgens from testes
In females: masculinizing effects (ie. excessive facial hair) |
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Adrenal medulla| From cells !! Effect |
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| Adrenaline (epinephrine) (Primarily) | Fight-or-flight response: | - Boost the supply of oxygen and glucose to the brain and muscles (by increasing heart rate and stroke volume, vasodilation, increasing catalysis of glycogen in liver, breakdown of lipids in adipocyte|fat cells)
| | - Suppress non-emergency bodily processes (e.g., digestion)
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| Noradrenaline (norepinephrine) | Chromaffin cells || Fight-or-flight response: | - Boost the supply of oxygen and glucose to the brain and muscles (by increasing heart rate and stroke volume, vasoconstriction and increased blood pressure, breakdown of lipids in adipocyte|fat cells)
| - Increase skeletal muscle readiness.
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| Dopamine | Chromaffin cells || Increase heart rate and blood pressure |
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| Enkephalin | Chromaffin cells || Regulate pain |
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Reproductive
Testes| From cells !! Effect |
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| Androgens (chiefly testosterone) | Leydig cells || Anabolic: growth of muscle mass and strength, increased bone density, growth and strength, | Virilizing: maturation of sex organs, formation of scrotum, deepening of voice, growth of beard and axillary hair. |
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| Estradiol | Sertoli cells || Prevent apoptosis of germ cells |
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| Inhibin | Sertoli cells || Inhibit production of follicle stimulating hormone|FSH |
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Ovarian follicle / Corpus luteum| From cells !! Effect |
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| Progesterone | Granulosa cells, Theca interna|theca cells || Support pregnancy: | - Convert uterine lining|endometrium to secretory stage
| - Make Cervix#Cervical_mucus|cervical mucus permeable to sperm.
| - Inhibit immune system|immune response, e.g., towards the human embryo
| - Decrease uterine smooth muscle contractility
| | - Inhibit onset of labor (childbirth)|labor.
| | Other: | - Raise epidermal growth factor-1 levels
| - Increase core temperature during ovulation
| - Reduce spasm and relax smooth muscle (widen bronchi and regulate mucus)
| Inflammation|Anti-inflammatory | - Reduce gall-bladder activity
| - Normalize blood clotting and vascular tone, zinc and copper levels, cell (biology)|cell oxygen levels, and use of fat stores for energy
| - Assist in thyroid function and bone growth by osteoblasts
| - Increase resilience in bone, teeth, gingiva|gums, joint, tendon, ligament, and human skin|skin
| - Promote healing by regulating collagen
| - Provide nerve function and healing by regulating myelin
| - Prevent endometrial cancer by regulating effects of estrogen
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| Androstenedione | Theca interna|Theca cells || Substrate for estrogen |
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| Estrogens (mainly estradiol) | Granulosa cells || Structural: | - Promote formation of female secondary sex characteristics
| | - Accelerate metabolism (burn fat)
| | - Stimulate endometrium|endometrial growth
| - Increase uterus|uterine growth
| - Maintain blood vessels and skin
| - Reduce bone resorption, increase bone formation
| Protein synthesis: | - Increase hepatic production of binding proteins
| Coagulation: | - Increase circulating level of coagulation factor|factors factor II|2, factor VII|7, factor IX|9, factor X|10, antithrombin III, plasminogen
| - Increase platelet adhesiveness
| - Increase high-density lipoprotein|HDL, triglyceride, height growth
| - Decrease low-density lipoprotein|LDL, fat deposition
| Fluid balance: | - Regulate salt (sodium) and water retention
| | | Gastrointestinal tract: | | - Increase cholesterol in bile
| Melanin: | - Increase pheomelanin, reduce eumelanin
| Cancer: | - Support hormone-sensitive breast cancers (Suppression of production in the body of estrogen is a treatment for these cancers.)
| Lung function: | - Promote lung function by supporting alveoli.
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| Inhibin | Granulosa cells || Inhibit production of follicle stimulating hormone|FSH from anterior pituitary |
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Placenta (when pregnant)| Abbreviation !! width=17% | From cells !! Effect |
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| Progesterone (Primarily) | || || Support pregnancy: | - Inhibit immune system|immune response, towards the fetus.
| - Decrease uterine smooth muscle contractility
| | - Inhibit onset of labor (childbirth)|labor.
| - Support fetal production of adrenal mineralo- and glucosteroids.
| Other effects on mother similar to ovarian follicle-progesterone |
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| Estrogens (mainly Estriol) (Also Primarily) | || || Effects on mother similar to ovarian follicle estrogen |
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| Human chorionic gonadotropin | HCG || Syncytiotrophoblast || promote maintenance of corpus luteum during beginning of pregnancy | Inhibit immune system|immune response, towards the human embryo. |
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| Human placental lactogen | HPL || Syncytiotrophoblast || increase production of insulin and IGF-1 | increase insulin resistance and carbohydrate intolerance |
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| Inhibin | || Fetal Trophoblasts || suppress follicle stimulating hormone|FSH |
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Uterus (when pregnant)| Abbreviation !! width=17% | From cells !! Effect |
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| Prolactin | PRL || Decidual cells || milk production in mammary glands |
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| Relaxin | || Decidual cells || Unclear in humans and animals |
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Calcium regulation
Parathyroid| Abbreviation !! width=17% | From cells !! Effect |
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| Parathyroid hormone | PTH || Parathyroid chief cell || Calcium: | - Stimulates Ca2+ release from bone, thereby increasing blood Ca2+
| - Stimulates osteoclasts, thus breaking down bone
| - Stimulates Ca2+ reabsorption in kidney
| - Stimulates activated vitamin D production in kidney
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Phosphate: | - Stimulates PO4= release from bones, thereby increasing blood PO4=
| - Inhibits PO4= reabsorption in kidney, so more PO4= is excreted
| - Overall, small net drop in serum PO4=
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Human skin|Skin| From cells !! Effect |
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| Calcidiol (25-hydroxyvitamin D3) | || Inactive form of Vitamin D3|vitamin D3 |
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Miscellaneous
Heart| Abbreviation !! width=17% | From cells !! Effect |
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| Atrial-natriuretic peptide | ANP || Cardiac muscle|Cardiac myocytes || Reduce blood pressure by: | reducing systemic circulation|systemic vascular resistance, | reducing blood water, sodium and blood fats|fats |
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| Brain natriuretic peptide | BNP || Cardiac muscle|Cardiac myocytes || (To a lesser degree than ANP) reduce blood pressure by: | reducing systemic circulation|systemic vascular resistance, | reducing blood water, sodium and blood fats|fats |
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Bone Marrow| From cells !! Effect |
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| Thrombopoietin | liver and kidney cells || stimulates megakaryocytes to produce platelets |
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Adipose tissue| From cells !! Effect |
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| Leptin (Primarily) | decrease of appetite and increase of metabolism. |
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| Estrogens (mainly Estrone) | |
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Major endocrine systems
The human endocrine system consists of several integrated systems that operate via feedback loops. Several important feedback systems are mediated via the hypothalamus and pituitary.
- Hypothalamic-pituitary-thyroid axis|TRH - TSH - T3/T4
- Hypothalamic-pituitary-gonadal axis|GnRH - LH/FSH - sex hormones
- Hypothalamic-pituitary-adrenal axis|CRH - ACTH - cortisol
- Renin-angiotensin system|Renin - angiotensin - aldosterone
Diseases
Endocrine diseases|Diseases of the endocrine system are common, including conditions such as diabetes mellitus, thyroid disease, and obesity.
Endocrine disease is characterized by disregulated hormone release (a productive pituitary adenoma), inappropriate response to signaling (hypothyroidism), lack of a gland (diabetes mellitus type 1, diminished erythropoiesis in chronic renal failure), or structural enlargement in a critical site such as the testis (toxic multinodular goitre). Hypofunction of endocrine glands can occur as a result of loss of reserve, hyposecretion, agenesis, atrophy, or active destruction. Hyperfunction can occur as a result of hypersecretion, loss of suppression, hyperplasia|hyperplastic or neoplastic change, or hyperstimulation.
Endocrinopathies are classified as primary, secondary, or tertiary. Primary endocrine disease inhibits the action of downstream glands. Secondary endocrine disease is indicative of a problem with the pituitary gland. Tertiary endocrine disease is associated with dysfunction of the hypothalamus and its releasing hormones.
As the Thyroid cancer|thyroid, and hormones have been implicated in signaling distant tissues to proliferate, for example, the estrogen receptor has been shown to be involved in certain breast cancers. Endocrine, paracrine, and autocrine signaling have all been implicated in proliferation, one of the required steps of oncogenesis.
Other types of signaling
The typical mode of cell signaling in the endocrine system is endocrine signaling. However, there are also other modes, i.e., paracrine, autocrine, and neuroendocrine signaling. Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system.
Autocrine
Autocrine signaling is a form of signaling in which a cell secretes a hormone or chemical messenger (called the autocrine agent) that binds to autocrine receptors on the same cell, leading to changes in the cells.
Paracrine
Paracrine signaling is a form of cell signaling in which the target cell is near the signal-releasing cell.
Juxtacrine
juxtacrine signaling is a type of intercellular communication that is transmitted via oligosaccharide, lipid, or protein components of a cell membrane, and may affect either the emitting cell or the immediately adjacent cells.
It occurs between adjacent cells that possess broad patches of closely opposed plasma membrane linked by transmembrane channels known as connexons. The gap between the cells can usually be between only 2 and 4 nm.
Unlike other types of cell signaling (such as paracrine and endocrine), juxtacrine signaling requires physical contact between the two cells involved.
Juxtacrine signaling has been observed for some growth factors, cytokine and chemokine cellular signals
See also
- Human anatomy#Major organ systems
References
Category:Endocrine system|
Category:Metabolic disorders
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This article is
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article "endocrine system".
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Last Modified: 2010-11-25 |
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