hypothalamus | Definition, Anatomy, & Function | Britannica

hypothalamus, region of the brain lying below the thalamus and making up the floor of the third cerebral ventricle. The hypothalamus is an integral part of ... hypothalamus TableofContents hypothalamus IntroductionAnatomyofthehypothalamusHypothalamicregulationofhormonesecretionHypothalamicdysfunction FastFacts 2-MinSummary RelatedContent Media Videos Images More MoreArticlesOnThisTopic Contributors ArticleHistory Home Health&Medicine Anatomy&Physiology hypothalamus anatomy Actions Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/hypothalamus GiveFeedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites Healthline-HypothalamusOverview ColoradoStateUniversity-HypertextforBiomedicalSciences-TheHypothalamusandPituitaryGland:IntroductionandIndex Print print Print Pleaseselectwhichsectionsyouwouldliketoprint: TableOfContents Cite verifiedCite Whileeveryefforthasbeenmadetofollowcitationstylerules,theremaybesomediscrepancies. Pleaserefertotheappropriatestylemanualorothersourcesifyouhaveanyquestions. SelectCitationStyle MLA APA ChicagoManualofStyle CopyCitation Share Share Sharetosocialmedia Facebook Twitter URL https://www.britannica.com/science/hypothalamus Feedback ExternalWebsites Feedback Corrections?Updates?Omissions?Letusknowifyouhavesuggestionstoimprovethisarticle(requireslogin). FeedbackType Selectatype(Required) FactualCorrection Spelling/GrammarCorrection LinkCorrection AdditionalInformation Other YourFeedback SubmitFeedback Thankyouforyourfeedback Oureditorswillreviewwhatyou’vesubmittedanddeterminewhethertorevisethearticle. JoinBritannica'sPublishingPartnerProgramandourcommunityofexpertstogainaglobalaudienceforyourwork! ExternalWebsites Healthline-HypothalamusOverview ColoradoStateUniversity-HypertextforBiomedicalSciences-TheHypothalamusandPituitaryGland:IntroductionandIndex By RobertD.Utiger • EditHistory TableofContents hypothalamus Seeallmedia KeyPeople: AndrewV.Schally RogerGuillemin ...(Showmore) RelatedTopics: ventromedialhypothalamus neuroendocrinecell mammillarybody chemoreceptortriggerzone thirstcentre ...(Showmore) Seeallrelatedcontent→ Summary Readabriefsummaryofthistopic hypothalamus,regionofthebrainlyingbelowthethalamusandmakingupthefloorofthethirdcerebralventricle.Thehypothalamusisanintegralpartofthebrain.Itisasmallcone-shapedstructurethatprojectsdownwardfromthebrain,endinginthepituitary(infundibular)stalk,atubularconnectiontothepituitarygland.Thehypothalamuscontainsacontrolcentreformanyfunctionsoftheautonomicnervoussystem,andithaseffectsontheendocrinesystembecauseofitscomplexinteractionwiththepituitarygland. Anatomyofthehypothalamus Thehypothalamusandpituitaryglandareconnectedbybothnervousandchemicalpathways.Theposteriorportionofthehypothalamus,calledthemedianeminence,containsthenerveendingsofmanyneurosecretorycells,whichrundownthroughtheinfundibularstalkintothepituitarygland.Importantstructuresadjacenttothemedianeminenceofthehypothalamusincludethemammillarybodies,thethirdventricle,andtheopticchiasm(apartofthevisualsystem).Abovethehypothalamusisthethalamus. BritannicaQuiz TheHumanBody Youmayknowthatthehumanbrainiscomposedoftwohalves,butwhatfractionofthehumanbodyismadeupofblood?Testbothhalvesofyourmindinthishumananatomyquiz. Hypothalamicregulationofhormonesecretion Thehypothalamus,liketherestofthebrain,consistsofinterconnectingneuronsthatarenourishedbyarichsupplyofblood.Tounderstandhypothalamicfunction,itisnecessarytodefinethevariousformsofneurosecretion.First,thereisneurotransmission,whichoccursthroughoutthebrainandistheprocessbywhichonenervecellcommunicateswithanotherviaasynapse,asmallgapbetweentheends(nerveterminals)ofneurons.Nerveterminalsareoftencalledpresynapticorpostsynapticinreferencetothedirectioninwhichanimpulseistraveling,withthepresynapticneurontransmittinganimpulsetothepostsynapticneuron.Transmissionofanelectricalimpulserequiresthesecretionofachemicalsubstancethatdiffusesacrossthesynapsefromthepresynapticmembraneofoneneurontothepostsynapticmembraneofanotherneuron.Thechemicalsubstancethatissecretediscalledaneurotransmitter.Theprocessofsynthesisandsecretionofneurotransmittersissimilartothatofproteinhormonesynthesis,withtheexceptionthattheneurotransmittersarecontainedwithinneurosecretorygranulesthatareproducedinthecellbodyandmigratethroughtheaxon(aprojectionoftheneuron)tothenerveterminal,fromwhichtheyaredischargedintothesynapticspace.Intracellularstructureofatypicalendocrinecell.Theprocessofproteinhormonesynthesisbeginswhenahormoneoranactivemetabolitestimulatesareceptorinthecellmembrane.ThisleadstotheactivationofspecificmoleculesofDNAinthenucleusandtheformationofaprohormone.Theprohormoneistransportedthroughtheendoplasmicreticulum,ispackagedintosecretoryvesiclesintheGolgiapparatus,andisultimatelysecretedfromthecellinitsactive,hormoneform.EncyclopædiaBritannica,Inc. Therearefourclassicneurotransmitters:epinephrine,norepinephrine,serotonin,andacetylcholine.Alargenumberofadditionalneurotransmittershavebeendiscovered,ofwhichanimportantgroupistheneuropeptides.Theneuropeptidesfunctionnotonlyasneurotransmittersbutalsoasneuromodulators.Asneuromodulators,theydonotactdirectlyasneurotransmittersbutratherincreaseordecreasetheactionofneurotransmitters.Well-knownexamplesaretheopioids(e.g.,enkephalins),sonamedbecausetheyareendogenous(producedinthehumanbody)peptides(shortchainsofaminoacids)withastrongaffinityforthereceptorsthatbindopiatedrugs,suchasmorphineandheroin. Thebrainandindeedtheentirecentralnervoussystemconsistofaninterconnectednetworkofneurons.Thesecretionofspecificneurotransmittersandneuropeptideslendsanorganized,directedfunctiontotheoverallsystem.Theconnectionofthehypothalamustomanyotherregionsofthebrain,includingthecerebralcortex,allowsintellectualandfunctionalsignals,aswellasexternalsignals,includingphysicalandemotionalstresses,tobefunneledintothehypothalamustotheendocrinesystem.Fromtheendocrinesystemthesesignalsareabletoexerttheireffectsthroughoutthebody. Thehypothalamusproducesandsecretesnotonlyneurotransmittersandneuropeptidesbutalsoseveralneurohormonesthatalteranteriorpituitaryglandfunctionandtwohormones,vasopressin(antidiuretichormone)andoxytocin,thatactondistanttargetorgans.Theneuronsthatproduceandsecreteneurohormonesaretrueendocrinecellsinthattheyproducehormonesthatareincorporatedintosecretorygranulesthatarethencarriedthroughtheaxonsandstoredinnerveterminalslocatedinthemedianeminenceorposteriorpituitarygland.Inresponsetoneuralstimuli,thecontentsofthesecretorygranulesareextrudedfromthenerveterminalsintoacapillarynetwork.Inthecaseofhormonesthataffectpituitaryfunction,thecontentsofthesecretorygranulesarecarriedthroughthehypophyseal-portalcirculationandaredelivereddirectlyintotheanteriorpituitarygland.Neurohormonesarereleasedfromneurosecretorynervecells.Thesenervecellsareconsideredtrueendocrinecellsbecausetheyproduceandsecretehormonesthatenterthecirculationtoreachtheirtargetcells.EncyclopædiaBritannica,Inc. Thesehypothalamicneurohormonesareknownasreleasinghormonesbecausetheirmajorfunctionistostimulatethesecretionofhormonesoriginatingintheanteriorpituitarygland.Forexample,certainreleasinghormonessecretedfromthehypothalamustriggerthereleasefromtheanteriorpituitaryofsubstancessuchasadrenocorticotropichormoneandluteinizinghormone.Thehypothalamicneurohormonesconsistofsimplepeptidesranginginsizefromonly3aminoacids(thyrotropin-releasinghormone)to44aminoacids(growthhormone-releasinghormone).Onehypothalamichormone,somatostatin,hasaninhibitoryaction,primarilyinhibitingthesecretionofgrowthhormonealthoughitcanalsoinhibitthesecretionofotherhormones.Theneurotransmitterdopamine,producedinthehypothalamus,alsohasaninhibitoryaction,inhibitingthesecretionoftheanteriorpituitaryhormoneprolactin.Thecellbodiesoftheneuronsthatproducetheseneurohormonesarenotevenlydistributedthroughoutthehypothalamus.Instead,theyaregroupedtogetherinpairedclustersofcellbodiesknownasnuclei. Aclassicmodelforneurohormonalactivityistheposteriorlobeofthepituitarygland(neurohypophysis).Itssecretoryproducts,vasopressinandoxytocin,areproducedandpackagedintoneurosecretorygranulesinspecificgroupsofnervecellsinthehypothalamus(thesupraopticnucleiandtheparaventricularnuclei).Thegranulesarecarriedthroughtheaxonsthatextendthroughtheinfundibularstalkandendinandformtheposteriorlobeofthepituitarygland.Inresponsetonervesignals,thesecretorygranulesareextrudedintoacapillarynetworkthatfeedsdirectlyintothegeneralcirculation. Understandthecauseoffeverandtheroleofthehypothalamusinregulatingthebody'stemperatureLearnaboutfevers,includingtheroleofthehypothalamus,whichregulatesthebody'stemperature.Contunico©ZDFEnterprisesGmbH,MainzSeeallvideosforthisarticleInadditiontoregulatingthereleaseofpituitaryhormones,thehypothalamusalsoinfluencescaloricintakeandweightregulation,establishingastable“setpoint”forindividualweightgain.Thehypothalamusalsoregulatesbodyheatinresponsetovariationsinexternaltemperature,determineswakefulnessandsleep,andregulatesfluidintakeandsensationofthirst. Hypothalamicdysfunction Injuriesordiseasesaffectingthehypothalamusmayproducesymptomsofpituitarydysfunctionordiabetesinsipidus;inthelatterdisorder,theabsenceofvasopressin,whichpromotesthereabsorptionofwaterinthekidneys,inducestherapidlossofwaterfromthebodythroughfrequenturination.Hypothalamicdiseasecanalsocauseinsomniaandfluctuationsinbodytemperature.Inaddition,theopticchiasmisparticularlysusceptibletopressurefromexpandingtumoursorinflammatorymassesinthehypothalamusorthepituitarygland.Pressureontheopticchiasmcanresultinvisualdefectsorevenblindness.RobertD.Utiger