HormonesintheBody Uptothebeginningofthetwentiethcentury,thenervoussystemwasthoughttocontrolallcommunicationwithinthebodyandtheresultingintegrationofbehavior.Scientistshaddeterminedthatnervesran,essentially,onelectricalimpulses.Theseimpulseswerethoughttobetheengineforthought,emotion,movement,andinternalprocessessuchasdigestion.However,experimentsbyWilliamBaylissandErnestStarlingonthechemicalsecretin,whichisproducedinthesmallintestinewhenfoodentersthestomach,eventuallychallengedthatview.Fromthesmallintestine,secretintravelsthroughthebloodstreamtothepancreas.There,itstimulatesthereleaseofdigestivechemicals.Inthisfashion,theintestinalcellsthatproducesecretinultimatelyregulatetheproductionofdifferentchemicalsinadifferentorgan,thepancreas. Suchacoordinationofprocesseshadbeenthoughttorequirecontrolbythenervoussystem;BaylissandStarlingshowedthatitcouldoccurthroughchemicalsalone.ThisdiscoveryspurredStartingtocointhetermhormonetorefertosecretin,takingitfromtheGreekwordhormon,meaning“toexcite”or“tosetinmotion.”Ahormoneisachemicalproducedbyonetissuetomakethingshappenelsewhere. Asmorehormoneswerediscovered,theywerecategorized,primarilyaccordingtotheprocessbywhichtheyoperatedonthebody.Someglands(whichmakeuptheendocrinesystem)secretehormonesdirectlyintothebloodstream.Suchglandsincludethethyroidandthepituitary.Theexocrinesystemconsistsoforgansandglandsthatproducesubstancesthatareusedoutsidethebloodstream,primarilyfordigestion.Thepancreasisonesuchorgan,althoughitsecretessomechemicalsintothebloodandthusisalsopartoftheendocrinesystem. Muchhasbeenlearnedabouthormonessincetheirdiscovery.Someplaysuchkeyrolesinregulatingbodilyprocessesorbehaviorthattheirabsencewouldcauseimmediatedeath.Themostabundanthormoneshaveeffectsthatarelessobviouslyurgentbutcanbemorefar-reachinganddifficulttotrack:Theymodifymoodsandaffecthumanbehavior,evensomebehaviorwenormallythinkofasvoluntary.Hormonalsystemsareveryintricate.Evenminuteamountsoftherightchemicalscansuppressappetite,calmaggression,andchangetheattitudeofaparenttowardachild.Certainhormonesacceleratethedevelopmentofthebody,regulatinggrowthandform;othersmayevendefineanindividual’spersonalitycharacteristics.Thequantitiesandproportionsofhormonesproducechangewithage,soscientistshavegivenagreatdealofstudytoshiftsintheendocrinesystemovertimeinthehopesofalleviatingailmentsassociatedwithaging. Infact,somehormonetherapiesarealreadyverycommon.Acombinationofestrogenandprogesteronehasbeenprescribedfordecadestowomenwhowanttoreducemoodswings,suddenchangesinbodytemperature,andotherdiscomfortscausedbylowernaturallevelsofthosehormonesastheyentermiddleage.Knownashormonereplacementtherapy(HRT),thetreatmentwasalsobelievedtopreventweakeningofthebones.AtleastonestudyhaslinkedHRTwithaheightenedriskofheartdiseaseandcertaintypesofcancer.HRTmayalsoincreasethelikelihoodthatbloodclots—dangerousbecausetheycouldtravelthroughthebloodstreamandblockmajorbloodvessels—willform.SomeproponentsofHRThavetemperedtheirenthusiasminthefaceofthisnewevidence,recommendingitonlytopatientswhosesymptomsinterferewiththeirabilitiestolivenormallives. Humangrowthhormonemayalsobegiventopatientswhoaresecretingabnormallylowamountsontheirown.Becauseofthecomplicatedeffectsgrowthhormonehasonthebody,suchtreatmentsaregenerallyrestrictedtochildrenwhowouldbepathologicallysmallinstaturewithoutit.Growthhormoneaffectsnotjustphysicalsizebutalsothedigestionoffoodandtheagingprocess.Researchersandfamilyphysicianstendtoagreethatitisfoolhardytodispenseitincasesinwhichtherisksarenotclearlyoutweighedbythebenefits. Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?
A.Most moods and actions are not voluntary because they are actually produced by the production of hormones in the body.
B.Because the effects of hormones are difficult to measure, scientists remain unsure how far-reaching their effects on moods and actions are.
C.When the body is not producing enough hormones, urgent treatment may be necessary to avoid psychological damage.
D.The influence of many hormones is not easy to measure, but they can affect both people’s psychology and actions extensively.
正确答案是D