Endocrine system

Major endocrine glands. (Male on the left, female on the right.) 1. Pineal gland 2. Pituitary gland 3. Thyroid gland 5. Adrenal gland 6. Pancreas 7. Ovary 8. Testis. Note: the Thymus (labelled 4.) is not an endocrine gland.

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. The endocrine system is an information signal system like the nervous system. 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.

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.

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.

Contents

Endocrine organs and secreted hormones

Central nervous system

Hypothalamus

Secreted hormone Abbreviation Produced by Effect
Thyrotropin-releasing hormone
(Prolactin-releasing hormone)		 TRH, TRF, or PRH Parvocellular neurosecretory neurons Stimulate thyroid-stimulating hormone (TSH) release from anterior pituitary (primarily)
Stimulate prolactin release from anterior pituitary
Dopamine
(Prolactin-inhibiting hormone)		 DA or PIH Dopamine neurons of the arcuate nucleus Inhibit prolactin release from anterior pituitary
Growth hormone-releasing hormone GHRH Neuroendocrine neurons of the Arcuate nucleus Stimulate Growth hormone (GH) release from anterior pituitary
Somatostatin
(growth hormone-inhibiting hormone)		 SS, GHIH, or SRIF Neuroendocrine cells of the Periventricular nucleus Inhibit Growth hormone (GH) release from anterior pituitary
Inhibit thyroid-stimulating hormone (TSH) release from anterior pituitary
Gonadotropin-releasing hormone GnRH or LHRH Neuroendocrine cells of the Preoptic area Stimulate follicle-stimulating hormone (FSH) release from anterior pituitary
Stimulate luteinizing hormone (LH) release from anterior pituitary
Corticotropin-releasing hormone CRH or CRF Parvocellular neurosecretory neurons Stimulate adrenocorticotropic hormone (ACTH) release from anterior pituitary
Oxytocin Magnocellular neurosecretory cells Uterine contraction
Lactation (letdown reflex)
Vasopressin
(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

Pineal body (epiphysis)

Secreted hormone From cells Effect
Melatonin (Primarily) Pinealocytes Antioxidant
Monitors the circadian rhythm including inducement of drowsiness
Dimethyltryptamine Speculated role in mystical and dream experiences

Pituitary Gland (hypophysis)

Anterior pituitary lobe (adenohypophysis)
Secreted hormone Abbreviation From cells Effect
Growth hormone
(somatotropin)		 GH Somatotrophs Stimulates growth and cell reproduction
Stimulates Insulin-like growth factor 1 release from liver
Thyroid-stimulating hormone
(thyrotropin)		 TSH Thyrotrophs Stimulates thyroxine (T4) and triiodothyronine (T3) synthesis and release from thyroid gland
Stimulates iodine absorption by thyroid gland
Adrenocorticotropic hormone
(corticotropin)		 ACTH Corticotrophs Stimulates corticosteroid (glucocorticoid and mineralcorticoid) and androgen synthesis and release from adrenocortical cells
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
Luteinizing hormone LH Gonadotrophs In females: Stimulates ovulation
In females: Stimulates formation of corpus luteum
In males: Stimulates testosterone synthesis from Leydig cells (interstitial cells)
Prolactin PRL Lactotrophs Stimulates milk synthesis and release from mammary glands
Mediates sexual gratification
Posterior pituitary lobe (neurohypophysis)
Secreted hormone Abbreviation From cells Effect
Oxytocin Magnocellular neurosecretory cells Uterine contraction
Lactation (letdown reflex)
Vasopressin
(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.

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

Thyroid

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
Thyroxine
(tetraiodothyronine)		 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
Calcitonin Parafollicular cells Stimulates osteoblasts and thus bone construction
Inhibits Ca2+ release from bone, thereby reducing blood Ca2+

Alimentary system

Stomach

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

secretion of growth hormone from anterior pituitary gland
Neuropeptide Y NPY increased food intake and decreased physical activity
Somatostatin 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.[1]
Histamine ECL cells stimulate gastric acid secretion
Endothelin X cells Smooth muscle contraction of stomach[2]

Duodenum

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 enzymes from pancreas

Release of bile from gallbladder hunger suppressant

Liver

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

regulate cell growth and development
Angiotensinogen and angiotensin Hepatocytes vasoconstriction

release of aldosterone from adrenal cortex dipsogen.
Thrombopoietin Hepatocytes stimulates megakaryocytes to produce platelets[3]

Pancreas

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

intake of lipids and synthesis of triglycerides in adipocytes Other anabolic effects
Glucagon (Also Primarily) α Islet cells glycogenolysis and gluconeogenesis in liver

increases blood glucose level
Somatostatin δ Islet cells Inhibit release of insulin[4]

Inhibit release of glucagon[4] Suppress the exocrine secretory action of pancreas.
Pancreatic polypeptide PP cells Self regulate the pancreas secretion activities and effect the hepatic glycogen levels.

Kidney

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
Thrombopoietin stimulates megakaryocytes to produce platelets[3]

Adrenal glands

Adrenal cortex

Secreted hormone From cells Effect
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)
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 H+ secretion into nephron of kidney and subsequent excretion
Androgens (including 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)

Adrenal medulla

Secreted hormone From cells Effect
Adrenaline (epinephrine) (Primarily) Chromaffin cells Fight-or-flight response:
Noradrenaline (norepinephrine) Chromaffin cells Fight-or-flight response:
Dopamine Chromaffin cells Increase heart rate and blood pressure
Enkephalin Chromaffin cells Regulate pain

Reproductive

Testes

Secreted hormone From cells Effect
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.
Estradiol Sertoli cells Prevent apoptosis of germ cells[5]
Inhibin Sertoli cells Inhibit production of FSH

Ovarian follicle / Corpus luteum

Secreted hormone From cells Effect
Progesterone Granulosa cells, theca cells Support pregnancy[6]:

Other:

  • Raise epidermal growth factor-1 levels
  • Increase core temperature during ovulation[7]
  • Reduce spasm and relax smooth muscle (widen bronchi and regulate mucus)

Anti-inflammatory
Androstenedione Theca cells Substrate for estrogen
Estrogens (mainly estradiol) 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

Coagulation:

Fluid balance:

Gastrointestinal tract:

  • Reduce bowel motility
  • Increase cholesterol in bile

Melanin:

Cancer:

  • Support hormone-sensitive breast cancers [9] (Suppression of production in the body of estrogen is a treatment for these cancers.)

Lung function:
Inhibin Granulosa cells Inhibit production of FSH from anterior pituitary

Placenta (when pregnant)

Secreted hormone Abbreviation From cells Effect
Progesterone (Primarily) Support pregnancy[6]:

Other effects on mother similar to ovarian follicle-progesterone
Estrogens (mainly Estriol) (Also Primarily) Effects on mother similar to ovarian follicle estrogen
Human chorionic gonadotropin HCG Syncytiotrophoblast promote maintenance of corpus luteum during beginning of pregnancy

Inhibit immune response, towards the human embryo.
Human placental lactogen HPL Syncytiotrophoblast increase production of insulin and IGF-1

increase insulin resistance and carbohydrate intolerance
Inhibin Fetal Trophoblasts suppress FSH

Uterus (when pregnant)

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

Calcium regulation

Parathyroid

Secreted hormone Abbreviation From cells Effect
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

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=

Skin

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

Miscellaneous

Heart

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

reducing systemic vascular resistance, reducing blood water, sodium and fats
Brain natriuretic peptide BNP Cardiac myocytes (To a lesser degree than ANP) reduce blood pressure by:

reducing systemic vascular resistance, reducing blood water, sodium and fats

Bone Marrow

Secreted hormone From cells Effect
Thrombopoietin liver and kidney cells stimulates megakaryocytes to produce platelets[3]

Adipose tissue

Secreted hormone From cells Effect
Leptin (Primarily) Adipocytes decrease of appetite and increase of metabolism.
Estrogens[11] (mainly Estrone) Adipocytes

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.[12]

Diseases

Disability-adjusted life year for endocrine disorders per 100,000 inhabitants in 2002.[13]
     no data      less than 80      80-160      160-240      240-320      320-400      400-480      480-560      560-640      640-720      720-800      800-1000      more than 1000

Diseases of the endocrine system are common,[14] 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, 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.[15]

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.[16] 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

References

  1. ↑ Colorado State University - Biomedical Hypertextbooks - Somatostatin
  2. ↑ Endo K, Matsumoto T, Kobayashi T, Kasuya Y, Kamata K (February 2005). "Diabetes-related changes in contractile responses of stomach fundus to endothelin-1 in streptozotocin-induced diabetic rats" (– Scholar search). J Smooth Muscle Res 41 (1): 35–47. doi:10.1540/jsmr.41.35. PMID 15855738. http://joi.jlc.jst.go.jp/JST.JSTAGE/jsmr/41.35?from=PubMed. 
  3. ↑ 3.0 3.1 3.2 Kaushansky K (May 2006). "Lineage-specific hematopoietic growth factors". N Engl J Med. 354 (19): 2034–45. doi:10.1056/NEJMra052706. PMID 16687716. 
  4. ↑ 4.0 4.1 Physiology at MCG 5/5ch4/s5ch4_17
  5. ↑ Pentikäinen V, Erkkilä K, Suomalainen L, Parvinen M, Dunkel L (May 2000). "Estradiol acts as a germ cell survival factor in the human testis in vitro". J Clin Endocrinol Metab. 85 (5): 2057–67. doi:10.1210/jc.85.5.2057. PMID 10843196. http://jcem.endojournals.org/cgi/pmidlookup?view=long&pmid=10843196. 
  6. ↑ 6.0 6.1 6.2 6.3 Placental Hormones
  7. ↑ Physiology at MCG 5/5ch9/s5ch9_13
  8. ↑ Hould F, Fried G, Fazekas A, Tremblay S, Mersereau W (1988). "Progesterone receptors regulate gallbladder motility". J Surg Res 45 (6): 505–12. doi:10.1016/0022-4804(88)90137-0. PMID 3184927. 
  9. ↑ Hormonal Therapy
  10. ↑ Massaro D, Massaro GD (2004). "Estrogen regulates pulmonary alveolar formation, loss, and regeneration in mice". American Journal of Physiology. Lung Cellular and Molecular Physiology 287 (6): L1154–9. doi:10.1152/ajplung.00228.2004. PMID 15298854. 
  11. ↑ Frühbeck G (July 2004). "The adipose tissue as a source of vasoactive factors". Curr Med Chem Cardiovasc Hematol Agents 2 (3): 197–208. doi:10.2174/1568016043356255. PMID 15320786. http://openurl.ingenta.com/content/nlm?genre=article&issn=1568-0169&volume=2&issue=3&spage=197&aulast=Frühbeck. 
  12. ↑ Sherwood, L. (1997). Human Physiology: From Cells to Systems. Wadsworth Pub Co 
  13. ↑ "Mortality and Burden of Disease Estimates for WHO Member States in 2002" (xls). World Health Organization. 2002. http://www.who.int/entity/healthinfo/statistics/bodgbddeathdalyestimates.xls. 
  14. ↑ Kasper et al. (2005). Harrison's Principles of Internal Medicine. McGraw Hill. pp. 2074. ISBN 0-07-139140-1. 
  15. ↑ Bhowmick NA, Chytil A, Plieth D, et al. (February 2004). "TGF-beta signaling in fibroblasts modulates the oncogenic potential of adjacent epithelia". Science 303 (5659): 848–51. doi:10.1126/science.1090922. PMID 14764882. 
  16. ↑ University of Virginia - HISTOLOGY OF THE ENDOCRINE GLANDS
Human systems and organs
TA 2-4:
MS
Bone (Carpus · Collar bone (clavicle) · Thigh bone (femur) · Fibula · Humerus · Mandible · Metacarpus · Metatarsus · Ossicles · Patella · Phalanges · Radius · Skull (cranium) · Tarsus · Tibia · Ulna · Rib · Vertebra · Pelvis · Sternum) · Cartilage
Fibrous joint · Cartilaginous joint · Synovial joint
TA 5-11:
splanchnic/
viscus
mostly
Thoracic
URT (Nose, Nasopharynx, Larynx) · LRT (Trachea, Bronchus, Lung)
mostly
Abdominopelvic
Mouth (Salivary gland, Tongue) · upper GI (Oropharynx, Laryngopharynx, Esophagus, Stomach) · lower GI (Small intestine, Appendix, Colon, Rectum, Anus) · accessory (Liver, Biliary tract, Pancreas)
Kidney · Ureter · Bladder · Urethra
Endocrine system
TA 12-16
peripheral (Artery, Vein, Lymph vessel) · Heart
primary (Bone marrow, Thymus) · secondary (Spleen, Lymph node)
Skin · Subcutaneous tissue · Breast (Mammary gland)
Blood
(Non-TA)
Myeloid
general anatomy: systems and organs, regional anatomy, , , superficial anatomy of limbs
Human anatomy, endocrine system: endocrine glands (TA A11, GA 11.1269)
Islets of pancreas
Alpha cell · Beta cell · Delta cell · PP cell · Epsilon cell
Hypothalamic/
pituitary axes
+parathyroid
Pituitary
Posterior pituitary

Pars nervosa · Median eminence · Infundibular stalk

Pituicyte · Herring bodies
Anterior pituitary

Pars intermedia · Pars tuberalis · Pars distalis

Acidophils (Somatotropes, Lactotropes) · Basophils (Corticotropes, Gonadotropes, Thyrotropes) · Chromophobe
Thyroid axis

Thyroid isthmus · Lobes of thyroid gland · Pyramidal lobe of thyroid gland

Parafollicular cell · Thyroid epithelial cell
Oxyphil cell · Chief cell
Adrenal axis:
Adrenal gland
Cortex
Zona glomerulosa · Zona fasciculata · Zona reticularis
Medulla
Chromaffin cells
Gonadal axis
Gonad: Testes · Ovaries · Corpus luteum
Pineal gland
Pinealocyte · Corpora arenacea

: END

anat/phys/devp/horm/cell

noco(d)//tumr, sysi/

proc, drug (A10/H1/H2//)
Cell physiology: signal transduction / cell signaling
Signaling pathways
GPCR (Hedgehog, Wnt) · RTK (TGF beta, MAPK/ERK) · Notch · JAK-STAT · Akt/PKB · Fas apoptosis · Hippo · Integrin receptors
Agents
Hormones · Neurotransmitters/Neuropeptides · Cytokines · Growth factors
Cell surface · Intracellular · Co-receptor
Signal transducing adaptor protein
Scaffold protein
2nd messenger
cAMP-dependent pathway · Ca2+ signaling · Lipid signaling · IP3/DAG pathway
General · Preinitiation complex · TFIID, TFIIH
By location
Intracrine · Autocrine · Juxtacrine · Paracrine · Endocrine
Other concepts
Signaling molecule · Ion channel gating · Mechanotransduction · Phototransduction · Synaptic transmission
trdu: iter (nrpl/grfl/cytl/horl), csrc (lgic, enzr, gprc, nrpr/grfr/), (, , ), , ; path (, , +, , , fsap, , )