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Endocrine system

The endocrine system is a chemical messengersystem comprising feedback loops of the hormonesreleased by internal glands of an organism directly intothe circulatory system, regulating distant target organs.In humans, the major endocrine glands are the thyroidgland and the adrenal glands. In vertebrates, thehypothalamus is the neural control center for allendocrine systems. The study of the endocrine systemand its disorders is known as endocrinology.Endocrinology is a branch of internal medicine.[1]

A number of glands that signal each other in sequenceare usually referred to as an axis, for example, the

hypothalamic-pituitary-adrenalaxis. In addition to thespecialized endocrine organsmentioned above, many otherorgans that are part of otherbody systems, including bone,kidney, liver, heart and gonads,have secondary endocrinefunctions. For example, thekidney secretes endocrinehormones such as erythropoietinand renin. Hormones can consistof either amino acid complexes,steroids, eicosanoids,leukotrienes, or prostaglandins.[1]

The endocrine system can becontrasted to both exocrineglands, which secrete hormonesto the outside of the body using

Endocrinesystem

Main glands of theendocrine system

Details

Identifiers

Latin Systemaendocrinum

MeSH D004703

FMA 9668

ducts and paracrine signallingbetween cells over a relativelyshort distance. Endocrine glandshave no ducts, are vascular and commonly haveintracellular vacuoles or granules that store theirhormones. In contrast, exocrine glands, such assalivary glands, sweat glands, and glands within thegastrointestinal tract, tend to be much less vascularand have ducts or a hollow lumen.

The word endocrine derives via New Latin from theGreek words ἔνδον, endon, "inside, within," and "crine"from the κρίνω, krīnō, "to separate, distinguish".

Major endocrine systems

The human endocrine system consists of severalsystems that operate via feedback loops. Several

Anatomicalterminology

Structure

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important feedback systems are mediated via thehypothalamus and pituitary.[2]

TRH – TSH – T3/T4

GnRH – LH/FSH – sex hormones

CRH – ACTH – cortisol

Renin – angiotensin – aldosterone

leptin vs. insulin

Glands

Endocrine glands are glands of the endocrine systemthat secrete their products, hormones, directly intointerstitial spaces and then absorbed into blood ratherthan through a duct. The major glands of the endocrinesystem include the pineal gland, pituitary gland,pancreas, ovaries, testes, thyroid gland, parathyroidgland, hypothalamus and adrenal glands. Thehypothalamus and pituitary gland are neuroendocrineorgans.

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Cells

There are many types of cells that comprise theendocrine system and these cells typically make uplarger tissues and organs that function within andoutside of the endocrine system.

Hypothalamus (Endocrine and Nervous Systems)Anterior pituitary glandPineal glandPosterior pituitary glandThyroid gland

Follicular cells of the thyroid gland produce andsecrete T3 and T4 in response to elevated levelsof TRH, produced by the hypothalamus, andsubsequent elevated levels of TSH, produced bythe anterior pituitary gland, which furtherregulates the metabolic activity and rate of allcells, including cell growth and tissuedifferentiation.

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Parathyroid glandEpithelial cells of the parathyroid glands arerichly supplied with blood from the inferior andsuperior thyroid arteries and secrete parathyroidhormone (PTH). PTH acts on bone, the kidneys,and the GI tract to increase calcium reabsorptionand phosphate excretion. In addition, PTHstimulates the conversion of Vitamin D to itsmost active variant, 1,25-dihydroxyvitamin D3,which further stimulates calcium absorption inthe GI tract.[1]

Adrenal glandsAdrenal cortex

Adrenal medullaPancreas

Alpha cells

Beta cells

Delta cells

F Cells

Ovary (female)Granulosa cells

Testicle (male)Leydig cells

Hormones

A hormone is any of a class of signaling moleculesproduced by glands in multicellular organisms that aretransported by the circulatory system to target distantorgans to regulate physiology and behaviour.Hormones have diverse chemical structures, mainly of3 classes: eicosanoids, steroids, and aminoacid/protein derivatives (amines, peptides, andproteins). The glands that secrete hormones comprise

This section needs expansion.

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Development

Function

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the endocrine system. The term hormone is sometimesextended to include chemicals produced by cells thataffect the same cell (autocrine or intracrine signalling)or nearby cells (paracrine signalling).

Hormones are used to communicate between organsand tissues for physiological regulation and behavioralactivities, such as digestion, metabolism, respiration,tissue function, sensory perception, sleep, excretion,lactation, stress, growth and development, movement,reproduction, and mood.[3][4]

Hormones affect distant cells by binding to specificreceptor proteins in the target cell resulting in a changein cell function. This may lead to cell type-specificresponses that include rapid changes to the activity ofexisting proteins, or slower changes in the expressionof target genes. Amino acid–based hormones (aminesand peptide or protein hormones) are water-soluble andact on the surface of target cells via signal transduction

pathways; steroid hormones, being lipid-soluble, movethrough the plasma membranes of target cells to actwithin their nuclei.

Cell signalling

The typical mode of cell signalling in the endocrinesystem is endocrine signaling, that is, using thecirculatory system to reach distant target organs.However, there are also other modes, i.e., paracrine,autocrine, and neuroendocrine signaling. Purelyneurocrine signaling between neurons, on the otherhand, belongs completely to the nervous system.

Autocrine

Autocrine signaling is a form of signaling in which a cellsecretes a hormone or chemical messenger (called theautocrine agent) that binds to autocrine receptors onthe same cell, leading to changes in the cells.

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Paracrine

Some endocrinologists and clinicians include theparacrine system as part of the endocrine system, butthere is not consensus. Paracrines are slower acting,targeting cells in the same tissue or organ. An exampleof this is somatostatin which is released by somepancreatic cells and targets other pancreatic cells.[1]

Juxtacrine

Juxtacrine signaling is a type of intercellularcommunication that is transmitted via oligosaccharide,lipid, or protein components of a cell membrane, andmay affect either the emitting cell or the immediatelyadjacent cells.[5]

It occurs between adjacent cells that possess broadpatches of closely opposed plasma membrane linkedby transmembrane channels known as connexons. The

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gap between the cells can usually be between only 2and 4 nm.[6]

Disease

Clinical significance

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Disability-adjusted life year for endocrine disorders per100,000 inhabitants in 2002.[7]

   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

Diseases of the endocrine system are common,[8]

including conditions such as diabetes mellitus, thyroiddisease, and obesity. Endocrine disease ischaracterized by misregulated hormone release (aproductive pituitary adenoma), inappropriate responseto signaling (hypothyroidism), lack of a gland (diabetesmellitus type 1, diminished erythropoiesis in chronickidney failure), or structural enlargement in a criticalsite such as the thyroid (toxic multinodular goitre).Hypofunction of endocrine glands can occur as a resultof loss of reserve, hyposecretion, agenesis, atrophy, oractive destruction. Hyperfunction can occur as a resultof hypersecretion, loss of suppression, hyperplastic orneoplastic change, or hyperstimulation.

Endocrinopathies are classified as primary, secondary,or tertiary. Primary endocrine disease inhibits theaction of downstream glands. Secondary endocrine

   more than 1000

disease is indicative of a problem with the pituitarygland. Tertiary endocrine disease is associated withdysfunction of the hypothalamus and its releasinghormones.[9]

As the thyroid, and hormones have been implicated insignaling distant tissues to proliferate, for example, theestrogen receptor has been shown to be involved incertain breast cancers. Endocrine, paracrine, andautocrine signaling have all been implicated inproliferation, one of the required steps ofoncogenesis.[10]

Other common diseases that result from endocrinedysfunction include Addison's disease, Cushing'sdisease and Graves' disease. Cushing's disease andAddison's disease are pathologies involving thedysfunction of the adrenal gland. Dysfunction in theadrenal gland could be due to primary or secondaryfactors and can result in hypercortisolism or

hypocortisolism . Cushing's disease is characterized bythe hypersecretion of the adrenocorticotropic hormone(ACTH) due to a pituitary adenoma that ultimatelycauses endogenous hypercortisolism by stimulatingthe adrenal glands.[11] Some clinical signs of Cushing'sdisease include obesity, moon face, and hirsutism.[12]

Addison's disease is an endocrine disease that resultsfrom hypocortisolism caused by adrenal glandinsufficiency. Adrenal insufficiency is significantbecause it is correlated with decreased ability tomaintain blood pressure and blood sugar, a defect thatcan prove to be fatal.[13]

Graves' disease involves the hyperactivity of the thyroidgland which produces the T3 and T4 hormones.[12]

Graves' disease effects range from excess sweating,fatigue, heat intolerance and high blood pressure toswelling of the eyes that causes redness, puffiness andin rare cases reduced or double vision.[6]

A neuroendocrine system has been observed in allanimals with a nervous system and all vertebrates havea hypothalamus-pituitary axis.[14] All vertebrates have athyroid, which in amphibians is also crucial fortransformation of larvae into adult form.[15][16] Allvertebrates have adrenal gland tissue, with mammalsunique in having it organized into layers.[17] Allvertebrates have some form of a renin–angiotensinaxis, and all tetrapods have aldosterone as a primarymineralocorticoid.[18][19]

Other animals

Additional images

Femaleendocrine system

Maleendocrine system

Endocrine disease

Endocrinology

List of human endocrine organs and actions

Melatonin

Neuroendocrinology

Nervous system

Paracrine signalling

Releasing hormones

See also

Sleep disorders

Tropic hormone

1. Marieb E (2014). Anatomy & physiology. Glenview,IL: Pearson Education, Inc. ISBN 978-0321861580.

2. Sherwood, L. (1997). Human Physiology: From Cellsto Systems. Wadsworth Pub Co. ISBN 978-0495391845.

3. Neave N (2008). Hormones and behaviour: apsychological approach. Cambridge: CambridgeUniv. Press. ISBN 978-0521692014. Lay summary– Project Muse.

4. "Hormones" . MedlinePlus. U.S. National Library ofMedicine.

5. Gilbert SF (January 1, 2000). "JuxtacrineSignaling" .

6. Vander A (2008). Vander's Human Physiology: themechanisms of body function . Boston: McGraw-

References

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7. "Mortality and Burden of Disease Estimates forWHO Member States in 2002" (xls). World HealthOrganization. 2002.

8. Kasper DL, Harrison TR (2005). Harrison's Principlesof Internal Medicine. McGraw Hill. p. 2074.ISBN 978-0-07-139140-5.

9. Macksey LF (2012). Surgical procedures andanesthetic implications: a handbook for nurseanesthesia practice. Sudbury, MA: Jones & BartlettLearning. p. 479. ISBN 9780763780579.OCLC 632070527 .

10. Bhowmick NA, Chytil A, Plieth D, Gorska AE, DumontN, Shappell S, Washington MK, Neilson EG, MosesHL (February 2004). "TGF-beta signaling infibroblasts modulates the oncogenic potential ofadjacent epithelia". Science. 303 (5659): 848–51.

Bibcode:2004Sci...303..848B .doi:10.1126/science.1090922 . PMID 14764882 .

11. Buliman A, Tataranu LG, Paun DL, Mirica A,Dumitrache C (2016). "Cushing's disease: amultidisciplinary overview of the clinical features,diagnosis, and treatment" . Journal of Medicine andLife. 9 (1): 12–18. PMC 5152600 .PMID 27974908 .

12. Vander A (2008). Vander's Human Physiology: themechanisms of body function . Boston: McGraw-Hill Higher Education. pp. 345–347 . ISBN 978-0073049625.

13. Inder WJ, Meyer C, Hunt PJ (June 2015)."Management of hypertension and heart failure inpatients with Addison's disease". ClinicalEndocrinology. 82 (6): 789–92.doi:10.1111/cen.12592 . PMID 25138826 .

14. Hartenstein V (September 2006). "Theneuroendocrine system of invertebrates: a

developmental and evolutionary perspective". TheJournal of Endocrinology. 190 (3): 555–70.doi:10.1677/joe.1.06964 . PMID 17003257 .

15. Dickhoff WW, Darling DS (1983). "Evolution ofThyroid Function and Its Control in LowerVertebrates". American Zoologist. 23 (3): 697–707.doi:10.1093/icb/23.3.697 . JSTOR 3882951 .

16. Galton VA (January 1, 1988). "The Role of ThyroidHormone in Amphibian Development". Integrativeand Comparative Biology. 28 (2): 309–18.doi:10.1093/icb/28.2.309 . JSTOR 3883279 .

17. Pohorecky LA, Wurtman RJ (March 1971)."Adrenocortical control of epinephrine synthesis".Pharmacological Reviews. 23 (1): 1–35.PMID 4941407 .

18. Wilson JX (1984). "The renin-angiotensin system innonmammalian vertebrates". Endocrine Reviews. 5(1): 45–61. doi:10.1210/edrv-5-1-45 .PMID 6368215 .

The Wikibook Human Physiology has a page on thetopic of: The endocrine system

The Wikibook Anatomy and Physiology of Animalshas a page on the topic of: Endocrine System

Media related to Endocrine system at WikimediaCommons

Retrieved from "https://en.wikipedia.org/w/index.php?title=Endocrine_system&oldid=938111178"

19. Colombo L, Dalla Valle L, Fiore C, Armanini D,Belvedere P (April 2006). "Aldosterone and theconquest of land". Journal of EndocrinologicalInvestigation. 29 (4): 373–9.doi:10.1007/bf03344112 . PMID 16699307 .

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