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Endocrine system


In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone into the bloodstream to regulate the body. It derives from the Greekένδο) meaning inside, within, and crinis (Greek κρινής) for secrete. 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, growth and development, tissue function, and metabolism. The field of study that deals with disorders of endocrine glands is endocrinology, a branch of internal medicine. words endo (Greek

The endocrine system is made up of a series of 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.

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

[edit] Central nervous system

Endocrine glands in the human head and neck and their hormones


Secreted hormone Abbreviation Produced by Effect
Thyrotropin-releasing hormone
(Prolactin-releasing hormone)
TRH, TRF, or PRH Parvocellular neurosecretory neurons Stimulate thyroid-stimulating hormone (TSH)anterior pituitary
Stimulate prolactinanterior pituitary
released from (primarily) release from
(Prolactin-inhibiting hormone)
DA or PIH Dopamine neurons of the arcuate nucleus Inhibit prolactinanterior pituitary released from
Growth hormone-releasing hormone GHRH NeuroendocrineArcuate nucleus neurons of the Stimulate Growth hormone (GH)anterior pituitary release from
(growth hormone-inhibiting hormone)
SS, GHIH, or SRIF NeuroendocrinePeriventricular nucleus cells of the Inhibit Growth hormone (GH)anterior pituitary
Inhibit thyroid-stimulating hormone (TSH)anterior pituitary
release from release from
Gonadotropin-releasing hormone GnRH or LHRH NeuroendocrinePreoptic area cells of the Stimulate follicle-stimulating hormone (FSH)anterior pituitary
Stimulate luteinizing hormone (LH) release from anterior pituitary
release from
Corticotropin-releasing hormone CRH or CRF Parvocellular neurosecretory neurons or the Paraventricular Nucleus Stimulate adrenocorticotropic hormone (ACTH)anterior pituitary release from
Oxytocin OT or OXT Magnocellular neurosecretory neurons of the Supraoptic Nucleus and Paraventricular Nucleus Uterine contraction
Lactation (letdown reflex)
(antidiuretic hormone)
ADH or AVP or VP Parvocellular neurosecretory neurons, Magnocellular neurosecretory neurons of the Paraventricular Nucleus and Supraoptic Nucleus Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume

Pineal body (epiphysis)

Secreted hormone From cells Effect
MelatoninDimethyltryptamine Pinealocytes Antioxidant
Monitors the circadian rhythmdrowsinesscore body temperature
including inducement of and lowering of the

Pituitary Gland (hypophysis)

Anterior pituitary lobe (adenohypophysis)
Secreted hormone Abbreviation From cells Effect
Growth hormone
GH Somatotrophs Stimulates growth and cell
Stimulates Insulin-like growth factor 1liver
reproduction release from
Thyroid-stimulating hormone
TSH Thyrotrophs Stimulates thyroxine (T4) and triiodothyroninethyroid gland
Stimulates iodine absorption by thyroid gland
(T3) synthesis and release from
Adrenocorticotropic hormone
ACTH Corticotrophs Stimulates corticosteroidglucocorticoidmineralcorticoid) and androgenadrenocortical cells ( and synthesis and release from
Beta-endorphin - Corticotrophs Inhibits perception of pain
Follicle-stimulating hormone FSH Gonadotrophs In females: Stimulates maturation of ovarian folliclesovary
In males: Stimulates maturation of seminiferous tubules
In males: Stimulates spermatogenesis
In males: Stimulates production of androgen-binding proteinSertoli cellstestes
in from of the
Luteinizing hormone LH Gonadotrophs In females: Stimulates ovulation
In females: Stimulates formation of corpus luteum
In males: Stimulates testosteroneLeydig cells (interstitial cells)
synthesis from
Prolactin. PRL Lactotrophs Stimulates milk synthesis and release from mammary glands
Mediates sexual gratification
Posterior pituitary lobe (neurohypophysis)
Secreted hormone Abbreviation From cells Effect
Magnocellular neurosecretory cells Uterine contraction
Lactation (letdown reflex)
(antidiuretic hormone)
ADH or AVP Parvocellular neurosecretory neurons Increases water permeability in the distal convoluted tubule and collecting duct of nephrons, thus promoting water reabsorption and increasing blood volume

Oxytocin and anti-diuretic hormone are not secreted in the posterior lobe, merely stored.

[edit] Intermediate pituitary lobe (pars intermedia)
Secreted hormone Abbreviation From cells Effect
Melanocyte-stimulating hormone MSH Melanotropes Stimulates melaninmelanocytes synthesis and release from skin/hair


Secreted hormone Abbreviation From cells Effect
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
T4 Thyroid epithelial cells (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
Parafollicular cells Stimulates osteoblasts and thus bone construction
Inhibits Ca2+2+
release from bone, thereby reducing blood Ca

Alimentary system

Endocrine Alimentary system en.svg


Secreted hormone Abbreviation From cells Effect
Gastrin (Primarily)
G cells Secretion of gastric acid by parietal cells
P/D1 cells Stimulate appetite,

secretion of growth hormone from anterior pituitary gland

Neuropeptide Y NPY
increased food intake and decreased physical activity
D cells Suppress release of gastrin, cholecystokininsecretin, motilin, vasoactive intestinal peptidegastric inhibitory polypeptideenteroglucagon (CCK), (VIP), (GIP),

Lowers rate of gastric emptying Reduces smooth muscle contractions and blood flow within the intestine.

ECL cells stimulate gastric acid secretion
X cells Smooth muscle contraction of stomach


Secreted hormone From cells Effect
Secretin S cells Secretion of bicarbonate from liver, pancreas and duodenal Brunner's glands

Enhances effects of cholecystokinin Stops production of gastric juice

Cholecystokinin I cells Release of digestive enzymespancreas from

Release of bile from gallbladder hunger suppressant


Secreted hormone Abbreviation From cells Effect
Insulin-like growth factor (or somatomedin) (Primarily) IGF Hepatocytes insulin-like effects

regulate cell growth and development

Angiotensinogenangiotensin and
Hepatocytes vasoconstriction

release of aldosterone from adrenal cortexdipsogen.

Hepatocytes stimulates megakaryocytesplatelets[3] to produce


Secreted hormone From cells Effect
Insulin (Primarily) β Islet cells Intake of glucose, glycogenesisglycolysis in liver and muscle from blood and

intake of lipids and synthesis of triglycerides in adipocytesanabolic effects Other

Glucagon (Also Primarily) α Islet cells glycogenolysis and gluconeogenesis in liver

increases blood glucose level

Somatostatin δ Islet cells Inhibit release of insulin

Inhibit release of glucagon pancreas. Suppress the exocrine secretory action of

Pancreatic polypeptide PP cells Self regulate the pancreas secretion activities and effect the hepatic glycogen levels.


Secreted hormone From cells Effect
Renin (Primarily) Juxtaglomerular cells Activates the renin-angiotensin system by producing angiotensin I of angiotensinogen
Erythropoietin (EPO) Extraglomerular mesangial cells Stimulate erythrocyte production
Calcitriol (1,25-dihydroxyvitamin D3)
Active form of vitamin D3

Increase absorption of calcium and phosphate from gastrointestinal tract and kidneys inhibit release of PTH

stimulates megakaryocytesplateletsto produce

Adrenal glands

Adrenal cortex

Secreted hormone From cells Effect
Glucocorticoidscortisol) (chiefly zona fasciculata and zona reticularis cells Stimulates gluconeogenesis
Stimulates fat breakdown
Inhibits protein synthesis
Inhibits glucose uptake in muscle and adipose tissue
Inhibits immunological responses (immunosuppressive)
Inhibits inflammatory responses (anti-inflammatory)
in adipose tissue
Mineralocorticoidsaldosterone) (chiefly Zona glomerulosa cells Stimulates active sodiumkidneys
Stimulates passive water reabsorption in kidneys, thus increasing blood volume and blood pressure
Stimulates potassium and H+ secretion into nephron
reabsorption in of kidney and subsequent excretion
AndrogensDHEAtestosterone) (including and Zona fasciculata and Zona reticularis cells In males: Relatively small effect compared to androgens from testes
In females: masculinizing effects (i.e. excessive facial hair)

Adrenal medulla

Secreted hormone From cells Effect
Adrenaline (epinephrine) (Primarily) Chromaffin cells Fight-or-flight response:
  • Boost the supply of oxygen and glucose to the brain and musclesheart rate and stroke volume, vasodilation, increasing catalysis of glycogen in liver, breakdown of lipids in fat cells) (by increasing
  • Dilate the pupils
  • Suppress non-emergency bodily processes (e.g., digestion)
  • Suppress immune system
Noradrenaline (norepinephrine) Chromaffin cells Fight-or-flight response:
  • Boost the supply of oxygen and glucose to the brain and musclesheart rate and stroke volume, vasoconstriction and increased blood pressure, breakdown of lipids in fat cells) (by increasing
  • Increase skeletal muscle readiness.
Dopamine Chromaffin cells Increase heart rate and blood pressure
Enkephalin Chromaffin cells Regulate pain


Endocrine reproductive system en.svg


Secreted hormone From cells Effect
Androgenstestosterone) (chiefly 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.

Estradiol Sertoli cells Prevent apoptosis of germ cells
Inhibin Sertoli cells Inhibit production of FSH

Ovarian follicle / Corpus luteum

Secreted hormone From cells Effect
Progesterone Granulosa cells, theca cells Support pregnancy[6]:
  • Convert endometrium to secretory stage
  • Make cervical mucus permeable to sperm.
  • Inhibit immunehuman embryo response, e.g., towards the
  • Decrease uterine smooth muscle contractility
  • Inhibit lactation
  • Inhibit onset of labor.


  • Raise epidermal growth factor-1 levels
  • Increase core temperature during ovulation
  • Reduce spasm and relax smooth muscle (widen bronchi and regulate mucus)


  • Reduce gall-bladderactivity
  • Normalize blood clotting and vascular tone, zinccopper levels, celloxygen levels, and use of fat stores for energy and
  • Assist in thyroidboneosteoblasts function and growth by
  • Increase resilience in bone, teeth, gums, joint, tendon, ligament, and skin
  • Promote healing by regulating collagen
  • Provide nerve function and healing by regulating myelin
  • Prevent endometrial cancer by regulating effects of estrogen
Androstenedione Theca cells Substrate for estrogen
Estrogensestradiol) (mainly Granulosa cells Structural:
  • Promote formation of female secondary sex characteristics
  • Accelerate height growth
  • Accelerate metabolism (burn fat)
  • Reduce muscle mass
  • Stimulate endometrial growth
  • Increase uterine growth
  • Maintain blood vessels and skin
  • Reduce bone resorption, increase bone formation

Protein synthesis:

  • Increase hepatic production of binding proteins


  • Increase circulating level of factors 2, 7, 9, 10, antithrombin III, plasminogen
  • Increase platelet adhesiveness
  • Increase HDL, triglyceride, height growth
  • Decrease LDL, fat deposition

Fluid balance:

  • Regulate salt (sodium) and water retention
  • Increase growth hormone
  • Increase cortisol, SHBG

Gastrointestinal tract:

  • Reduce bowel motility
  • Increase cholesterol in bile


  • Increase pheomelanin, reduce eumelanin


  • 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.
Inhibin Granulosa cells Inhibit production of FSHanterior pituitary from

Placenta (when pregnant)

Secreted hormone Abbreviation From cells Effect
Progesterone (Primarily)

Support pregnancy[6]:
  • Inhibit immunefetus. response, towards the
  • Decrease uterine smooth muscle[6] contractility
  • Inhibit lactation
  • Inhibit onset of labor.
  • Support fetaladrenal production of mineralo- and glucosteroids.

Other effects on mother similar to ovarian follicle-progesterone

EstrogensEstriol) (Also Primarily) (mainly

Effects on mother similar to ovarian follicle estrogen
Human chorionic gonadotropin HCG Syncytiotrophoblast promote maintenance of corpus luteumpregnancy during beginning of

Inhibit immunehuman embryo. response, towards the

Human placental lactogen HPL Syncytiotrophoblast increase production of insulin and IGF-1

increase insulin resistance and carbohydrate intolerance

Fetal Trophoblasts suppress FSH

Uterus (when pregnant)

Secreted hormone Abbreviation From cells Effect
Prolactin PRL Decidual cells milk production in mammary glands
Decidual cells Unclear in humans and animals

[edit] Calcium regulation

Endocrine caclcium en.svg


Secreted hormone Abbreviation From cells Effect
Parathyroid hormone PTH Parathyroid chief cell Calcium:
  • Stimulates Ca2+2+ release from bone, thereby increasing blood Ca
  • Stimulates osteoclasts, thus breaking down bone
  • Stimulates Ca2+kidney reabsorption in
  • Stimulates activated vitamin D production in kidney


  • Stimulates PO44. release from bones, thereby increasing blood PO
  • Inhibits PO4kidney, so more PO4 = is excreted reabsorption in
  • Overall, small net drop in serum PO4.


Secreted hormone From cells Effect
Calcidiol3) (25-hydroxyvitamin D
Inactive form of vitamin D3


Endocrine miscelaneous en.svg


Secreted hormone Abbreviation From cells Effect
Atrial-natriuretic peptide ANP Cardiac myocytes Reduce blood pressure by:

reducing systemicvascular resistance, reducing blood water, sodium and fats

Brain natriuretic peptide BNP Cardiac myocytes (To a lesser degree than ANP) reduce blood pressure by:

reducing systemicvascular resistance, reducing blood water, sodium and fats

Bone Marrow

Secreted hormone From cells Effect
Thrombopoietin liver and kidney cells stimulates megakaryocytes to produce platelets

Adipose tissue

Secreted hormone From cells Effect
Leptin (Primarily) Adipocytes decrease of appetite and increase of metabolism.
Estrogens Estrone) (mainly Adipocytes

Major endocrine systems

The human endocrine system consists of several systems that operate via feedback loops. Several important feedback systems are mediated via the hypothalamus and pituitary.

  • TRH - TSH - T3/T4
  • GnRH - LH/FSH - sex hormones
  • CRH - ACTH - cortisol
  • Renin - angiotensin - aldosterone


Disability-adjusted life year for endocrine disorders per 100,000 inhabitants in 2002.[13]
  no data
  less than 80
  more than 1000

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 thyroid (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, 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, 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[16] Purely neurocrine signaling between neurons, on the other hand, belongs completely to the nervous system. signaling.


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 signaling is a form of cell signaling in which the target cell is near the signal-releasing cell.


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

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