医学英语原文翻译1至5单元

1.isthestudyofthefunctionsoflivingmatter.Itisconcernedwithhowanorganismperformsitsvariedactivities:howitfeeds,howitmoves,howitadaptstochangingcircumstances,howitspawnsnewgenerations.Thesubjectisvastandembracesthewholeoflife.Thesuccessofphysiologyinexplaininghoworganismsperformtheirdailytasksisbasedonthenotionthattheyareintricateandexquisitemachineswhoseoperationisgovernedbythelawsofphysicsandchemistry.Althoughsomeprocessesaresimilaracrossthewholespectrumofreplicationofthegeneticcodeforexample—manyarespecifictoparticulargroupsoforganisms.Forthisreasonitisnecessarytodividethesubjectintovariouspartssuchasbacterialphysiology,plantphysiology,andanimalphysiology.2.正如要了解一个动物如何活动，首先需要了解它的构成，要充分了解一个生物体的生理学活动就必须掌握全面的解剖学知识。一个生物体的各部分起着什么作用可通过实验观察得知Tostudyhowananimalworksitisfirstnecessarytoknowhowitisbuilt.Afullappreciationofthephysiologyofanorganismmustthereforebebasedonasoundknowledgeofitsanatomy.Experimentscanthenbecarriedouttoestablishhowparticularpartsperformtheirfunctions.Althoughtherehavebeenmanyimportantphysiologicalinvestigationsonhumanvolunteers,theneedforprecisecontrolovertheexperimentalconditionshasmeantthatmuchofourpresentphysiologicalknowledgehasbeenderivedfromstudiesonotheranimalssuchasfrogs,rabbits,cats,anddogs.Whenitisclearthataspecificphysiologicalprocesshasacommonbasisinawidevarietyofanimalspecies,itisreasonabletoassumethatthesameprincipleswillapplytohumans.Theknowledgegainedfromthisapproachhasgivenusagreatinsightintohumanphysiologyandendoweduswithasolidfoundationfortheeffectivetreatmentofmanydiseases.Theorganizationofthebody3.机体的基本组成物质是细胞，细胞结合在一大脑，脊髓，自主神经和神经中枢以及周围躯体神经组成神经系统等等。3.Thebuildingblocksofthebodyarethecells,whicharegroupedtogethertoformtissues.Theprincipaltypesoftissueareepithelial,connective,nervous,andmuscular,eachwithitsowncharacteristics.Manyconnectivetissueshaverelativelyfewcellsbuthaveanextensiveextracellularmatrix.Incontrast,smoothmuscleconsistsofdenselypackedlayersofmusclecellslinkedtogetherviaspecificcelljunctions.Organssuchasthebrain,theheart,thelungs,theintestines,andtheliverareformedbytheaggregationofdifferentkindsoftissues.Theorgansarethemselvespartsofdistinctphysiologicalsystems.Theheartandbloodvesselsformthecardiovascularsystem;thelungs,trachea,andbronchitogetherwiththechestwallanddiaphragmformtherespiratorysystem;theskeletonandskeletalmusclesformthemusculoskeletalsystem;thebrain,spinalcord,autonomicnervesandganglia,andperipheralsomaticnervesformthenervoussystem,andsoon.4.第一，细胞由一层薄膜也称细胞膜包被；第二，细胞能把大分子分解为小分子释放能量供活(DNA)4.Cellsdifferwidelyinformandfunctionbuttheyallhavecertaincommoncharacteristics.First,theyareboundedbyalimitingmembrane,theplasmamembrane.Secondly,theyhavetheabilitytobreakdownlargemoleculestosmalleronestoliberateenergyfortheiractivities.Thirdly,atsomepointintheirlifehistory,theypossessanucleuswhichcontainsgeneticinformationintheformofdeoxyribonucleicacid(DNA).5.活体细胞不断转化物质。细胞分解葡萄糖和脂肪，为自身生长和修复所需的蛋白质合成和运动等其它活动提供能量。这些化学变化统称为新陈代谢。把大分子分解为小分子的过程称为分解代谢，小分子合成大分子的过程称为合成代谢。5.Livingcellscontinuallytransformmaterials.Theybreakdownglucoseandfatstoprovideenergyforotheractivitiessuchasmotilityandthesynthesisofproteinsforgrowthandrepair.Thesechemicalchangesarecollectivelycalledmetabolism.Thebreakdownoflargemoleculestosmalleronesiscalledcatabolismandthesynthesisoflargemoleculesfromsmalleronesanabolism.6.细胞在进化过程中不断分化进行不同的功能活动。有些细胞具有收缩能力（如肌细胞，有些可以传导电信号（如神经细胞。进一步进化的细胞能（如内分泌细胞）6.Inthecourseofevolution,cellsbegantodifferentiatetoservedifferentfunctions.Somedevelopedtheabilitytocontract(musclecells),otherstoconductelectricalsignals(nervecells).Afurthergroupdevelopedtheabilitytosecretedifferentsubstancessuchashormonesorenzymes.Duringembryologicaldevelopment,thisprocessofdifferentiationisre-enactedasmanydifferenttypesofcellareformedfromthefertilizedegg.7.大多数组织包含有不同的细胞类Mosttissuescontainamixtureofcelltypes.Forexample,bloodconsistsofredcells,whitecells,andplatelets.Redcellstransportoxygenaroundthebody.Thewhitecellsplayanimportantroleindefenseagainstinfectionandtheplateletsarevitalcomponentsintheprocessofbloodclotting.Thereareanumberofdifferenttypesofconnectivetissuebutallarecharacterizedbyhavingcellsdistributedwithinanextensivenoncellularmatrix.Nervetissuecontainsnervecellsandglialcells.8.大型多细胞动物体的细胞不能产生氧气和营养物质，需能之一，血液凭借心脏的泵血作用在血管内流动循环。Thecellsoflargemulticellularanimalscannotderivetheoxygenandnutrientstheyneeddirectlyfromtheexternalenvironment.Thesemustbetransportedtothecells.Thisisoneoftheprincipalfunctionsoftheblood,whichcirculateswithinbloodvesselsbyvirtueofthepumpingactionoftheheart.Theheart,bloodvessels,andassociatedtissuesformthecardiovascularsystem.Theheartconsistsoffourchambers,twoatriaandtwoventricles,whichformapairofpumpsarrangedsidebyside.Therightventriclepumpsdeoxygenatedbloodtothelungswhereitabsorbsoxygenfromtheair,whiletheleftventriclepumpsoxygenatedbloodreturningfromthelungstotherestofbodytosupplythetissues.Physiologistsareconcernedwithestablishingthefactorsresponsiblefortheheartbeat,howtheheartpumpsthebloodaroundthecirculation,andhowitisdistributedtoperfusethetissuesaccordingtotheirneeds.Fluidexchangedbetweenthebloodplasmaandthetissuespassesintothelymphaticsystem,whicheventuallydrainsbackintotheblood.（主要是糖类和脂肪）氧气频率的因素是什么？Theenergyrequiredforperformingthevariousactivitiesofthebodyisultimatelyderivedfromrespiration.Thisprocessinvolvestheoxidationoffoodstuffstoreleasetheenergytheycontain.Theoxygenneededforthisprocessisabsorbedfromtheairinthelungsandcarriedtothetissuesbytheblood.Thecarbondioxideproducedbytherespiratoryactivityofthetissuesiscarriedtothelungsbythebloodinthepulmonaryarterywhereitisexcretedintheexpiredair.Thebasicquestionstobeansweredincludethefollowing:Howistheairmovedinandoutofthelungs?Howisthevolumeofairbreathedadjustedtomeettherequirementsofthebody?Whatlimitstherateofoxygenuptakeinthelungs?机体所需营养物质来源于饮食。食物经口腔进入体内，在胃肠道内经酶将其分解成小分何消化的？食物如何被个体分解消化？个体营养物质如何吸收？食物如何在肠内转运的？Thenutrientsneededbythebodyarederivedfromthediet.Foodistakeninbythemouthandbrokendownintoitscomponentpartsbyenzymesinthegastrointestinaltract.Thedigestiveproductsarethenabsorbedintothebloodacrossthewalloftheintestineandpasstotheliverviatheportalvein.Thelivermakesnutrientsavailabletothetissuesbothfortheirgrowthandrepairandfortheproductionofenergy.Inthecaseofthedigestivesystem,keyphysiologicalquestionsare:Howisfoodingested?Howisitbrokendownanddigested?Howaretheindividualnutrientsabsorbed?Howisthefoodmovedthroughthegut?Howaretheindigestibleremainseliminatedfromthebody?肾脏主要功能是控制细胞外液体的形成。在这一过程中，肾脏也会把不可挥发的废物排应对像脱水这样的应激反应？以及尿液可以存储和排出体外的机制是什么？12.Thechieffunctionofthekidneysistocontrolthecompositionoftheextracellularfluid.Inthecourseofthisprocess,theyalsoeliminatenon-volatilewasteproductsfromtheblood.Toperformthesefunctions,thekidneysproduceurineofvariablecompositionwhichistemporarilystoredinthebladderbeforevoiding.Thekeyphysiologicalquestionsinthiscaseare:howdothekidneysregulatethecompositionoftheblood?Howdotheyeliminatetoxicwaste?Howdotheyrespondtostressessuchasdehydration?Whatmechanismsallowthestorageandeliminationoftheurine?Thereproductivesystem13.生殖是活生物体的一个基本特征。生殖腺产生专门的性细胞，被称为配子。性生殖的核心是雌雄配子即精子和卵子的产生和融合，因此两个独立个体的基因特征融合而产生一个基因上与双亲不同的后代。13.Reproductionisoneofthefundamentalcharacteristicsoflivingorganisms.Thegonadsproducespecializedsexcellsknownasgametes.Atthecoreofsexualreproductionisthecreationandfusionofthemaleandfemalegametes,thespermandova(eggs),withtheresultthatthegeneticcharacteristicsoftwoseparateindividualsaremixedtoproduceoffspringthatdiffergeneticallyfromtheirparents.14.这一系统由骨、骨骼肌、关节和它们的相关组织组成。其主要功能是提供运动需要，维分泌系统和神经系统14.Thisconsistsofthebonesoftheskeleton,skeletalmuscles,joints,andtheirassociatedtissues.Itsprimaryfunctionistoprovideameansofmovement,whichisrequiredforlocomotion,forthemaintenanceofposture,andforbreathing.ItalsoprovidesphysicalsupportfortheinternalorgansHerethemechanismofmusclecontractionisacentralissue.Theendocrineandnervoussystems15.不同器官系统的活动需要协作和调节，以便共同作用满足机体需要。人体有两大调节系15.Theactivitiesofthedifferentorgansystemsneedtobecoordinatedandregulatedsothattheyacttogethertomeettheneedsofthebody.Twocoordinatingsystemshaveevolved:thenervoussystemandtheendocrinesystem.Thenervoussystemuseselectricalsignalstotransmitinformationveryrapidlytospecificcells.Thusthenervespasselectricalsignalstotheskeletalmusclestocontroltheircontraction.Theendocrinesystemsecreteschemicalagents,hormones,whichtravelinthebloodstreamtothecellsuponwhichtheyexertaregulatoryeffect.Hormonesplayamajorroleintheregulationofmanydifferentorgansandareparticularlyimportantintheregulationofthemenstrualcycleandotheraspectsofreproduction.16.免疫系统通过杀死入侵的有机体，清除致病或损伤细胞为机体提供防御功能。Theimmunesystemprovidesthedefensesagainstinfectionbothbykillinginvadingorganismsandbyeliminatingdiseasedordamagedcells.Althoughitishelpfultostudyhoweachorganperformsitsfunctions,itisessentialtorecognizethattheactivityofthebodyasawholeisdependentontheintricateinteractionsbetweenthevariousorgansystems.Ifonepartfails,theconsequencesarefoundinotherorgansystemsthroughoutthewholebody.Forexample,ifthekidneysbegintofail,theregulationoftheinternalenvironmentisimpairedwhichinturnleadstodisordersoffunctionelsewhere.各种复杂机制共同作用调节细胞外液的形成，不同个体细胞有自身机制调节内在组成成被称为稳态，它是机体能够正常发挥作用所必须的。18.Complexmechanismsareatworktoregulatethecompositionoftheextracellularfluidandindividualcellshavetheirownmechanismsforregulatingtheirinternalcomposition.Theregulatorymechanismsstabilizetheinternalenvironmentdespitevariationsinboththeexternalworldandtheactivityoftheanimal.Theprocessofstabilizationoftheinternalenvironmentiscalledhomeostasisandisessentialifthecellsofthebodyaretofunctionnormally.例如，心脏的跳动依赖于心肌细胞有节律的收缩。这一活动依赖于电信号，而电信号反子的浓度就必须控制在一定范围内。Totakeoneexample,thebeatingoftheheartdependsontherhythmicalcontractionsofcardiacmusclecells.Thisactivitydependsonelectricalsignalswhich,inturn,dependontheconcentrationofsodiumandpotassiumionsintheextracellularandintracellularfluids.Ifthereisanexcessofpotassiumintheextracellularfluid,thecardiacmusclecellsbecometooexcitableandmaycontractatinappropriatetimesratherthaninacoordinatedmanner.Consequently,theconcentrationofpotassiumintheextracellularfluidmustbekeptwithinanarrowrangeiftheheartistobeatnormally.1千克食物，2-330千克食物，60-90升液体。然而，一般来说，机体体重是基本不变的。这类个体可以说处于Inthecourseofaday,anadultconsumesapproximately1kgoffoodanddrinkslitersoffluid.Inamonth,thisisequivalenttoaround30kgoffoodandlitersoffluid.Yet,ingeneral,bodyweightremainsremarkablyconstant.Suchindividualsaresaidtobeinbalance;theintakeoffoodanddrinkmatchestheamountsusedtogenerateenergyfornormalbodilyactivitiesplusthelossesinurineandfeces.Insomecircumstances,suchasstarvation,intakedoesnotmatchtheneedsofthebodyandmuscletissueisbrokendowntoprovideglucoseforthegenerationofenergy.Here,theintakeofproteinislessthantherateofbreakdownandtheindividualissaidtohaveanegativenitrogenbalance.Equally,ifthebodytissuesarebeingbuiltup,asisthecaseforgrowingchildren,pregnantwomenandathletesintheearlystagesoftraining,thedailyintakeofproteinisgreaterthanthenormalbodyturnoverandtheindividualisinpositivenitrogenbalance.平衡的概念可以应用到机体的任何构成成分上，包括水和盐，而且平衡在机体调节其自4-5mmol.l–1.进食后不久，血糖含量超过这一范围，刺激胰腺分泌在胰岛素分泌期间，葡萄糖像肝糖原或脂肪一样被储存。Thisconceptofbalancecanbeappliedtoanyofthebodyconstituentsincludingwaterandsaltandisimportantinconsideringhowthebodyregulatesitsowncomposition.Intakemustmatchrequirementsandanyexcessmustbeexcretedforbalancetobemaintained.Additionally,foreachchemicalconstituentofthebodythereisadesirableconcentrationrange,whichthecontrolmechanismsareadaptedtomaintain.Forexample,theconcentrationofglucoseintheplasmaisaboutmmol.l–1betweenmeals.Shortlyafterameal,plasmaglucoserisesabovethislevelandthisstimulatesthesecretionofthehormoneinsulinbythepancreas,whichactstobringtheconcentrationdown.Astheconcentrationofglucosefalls,sodoesthesecretionofinsulin.Ineachcase,thechangesinthecirculatinglevelofinsulinacttomaintaintheplasmaglucoseatanappropriatelevel.Thistypeofregulationisknownasnegativefeedback.Duringtheperiodofinsulinsecretion,theglucoseisbeingstoredaseitherglycogenorfat.负反馈环是在机体出现紊乱时，将一些变量控制在限定范围内的一个控制系统。虽然上加热器关闭。anegativefeedbackloopisacontrolsystemthatactstomaintainthelevelofsomevariablewithinagivenrangefollowingadisturbance.Althoughtheexamplegivenabovereferstoplasmaglucose,thebasicprinciplecanbeappliedtootherphysiologicalvariablessuchasbodytemperature,bloodpressure,andtheosmolalityoftheplasma.anegativefeedbacklooprequiresasensorofsomekindthatrespondstothevariableinquestionbutnottootherphysiologicalbariables,thusanosmoreceptorshouldrespindtochangesinosmolalityofthebodyfluidsbutnottochangesinbodytemperatureorbloodpressure.theinformationfromthesensormustbecomparedinsomewaywiththedesiredlevelbysomeformofcomparator.ifthetwodonotmatch,anerrorsignalistransmittedtoaneffector,asystemthatcanacttorestorethevariabletoitsdesiredlevel.thesefeaturesofnegativefeedbackcanbeappreciatedbyexaminingasimpleheatingsystem.thecontrolledvariableisroomtemperature,whichissensedbyathermostat.theeffectorisaheaterofsomekind.whentheroomtemperaturefallsbelowthesetpoint,thetemperaturedifferenceisdetectedbythethermostatwhichswitchesontheheater.thisheatstheroomuntilthetemperaturereachesthepersetlevelwhereupontheheaterisswitchedoff.23.总而言之，机体实际上是由100万亿细胞有序组成了不同的功能结构，其中一些被称为致疾病的发生。23.Tosumarize,thebodyisactuallyasocialorderofabout100trillioncellsorganizedintodifferentfunctionalstructures,someofwhicharecalledorgans.eachfunctionalstructuresitssharetothemaintenanceofhomeostaticconditionsintheextracellularfluid,whichiscalledtheinternalenvironment.aslongasnormalconditionsaremaintainedinthisinternalenvironment,thecellsofthebodycontinuetoliveandfunctionproperly.Eachcellbenefitsfromhomeostasis,andinturn,eachcellcontributesitssharetowardthemaintenanceofhomeostasis.Thisreciprocalinterplayprovidescontinuousautomaticityofthebodyuntiloneormorefunctionalsystemslosetheirabilitytocontributetheirshareoffunction.Whenthishappens,allthecellsofthebodysuffer.Extremedysfunctionleadstodeath;moderatedysfunctionleadstosickness.,是两个心房的同时收缩Thecardiaccycleisthesequenceofeventsinoneheartbeat.Initssimplestform,thecardiaccycleisthesimultaneouscontractionofthetwoatria,followedafractionofasecondlaterbythesimultaneouscontractionofthetwoventricles.Thereis,however,asignificantdifferencebetweenthemovementofbloodfromtheatriatotheventricles,andthemovementofbloodfromtheventriclestothearteries.血液的压力会打开左右房室瓣。两个心房里三分之二的血液被动地流入到心室中;然后，心房收缩将剩余血液泵入心室。Bloodisconstantlyflowingfromtheveinsintobothatria.Asmorebloodaccumulates,itspressureforcesopentherightandleftAVvalves.Twothirdsoftheatrialbloodflowspassivelyintotheventricles;theatriathencontracttopumptheremainingbloodintotheventricles.心房收缩后舒张，心室开始收缩。心室的收缩使血液施压于左右房室瓣的皮瓣并使其闭合同时血液继续流入心房，循环重新开始。Followingtheircontraction,theatriarelaxandtheventriclesbegintocontract.VentricularcontractionforcesbloodagainsttheflapsoftherightandleftAVvalvesandclosesthem;theforceofbloodalsoopenstheaorticandpulmonarysemilunarvalves.Astheventriclescontinuetocontract,theypumpbloodintothearteries.Thebloodthatentersthearteriesmustallbepumped.Theventriclesthenrelax,andatthesametimebloodcontinuestoflowintotheatria,andthecyclewillbeginagain.这里一个重要的不同点就是大部分血液是被动地从心房流入心室,但是所有注入动脉的血液均由心室主动射出。因此,对生存来说，心室的正常工作远比心房的工作重要的多。Theimportantdistinctionhereisthatmostbloodflowspassivelyfromatriatoventricles,butallbloodtothearteriesisactivelypumpedbytheventricles.Forthisreason,theproperfunctioningoftheventriclesismuchmorecrucialtosurvivalthanisatrialfunctioning.收缩的另一个术语是心脏收缩。松弛的术语是心脏舒张。您可能比较熟悉这些术语，因为,张。Thereisanothertermforcontraction,andthatissystole.Thetermforrelaxationisdiastole.Youareprobablyfamiliarwiththesetermsastheyrelatetobloodpressurereadings.Ifweapplythemtothecardiaccycle,wecansaythatatrialsystoleisfollowedbyventricularsystole.Anotherwaytoputitisthatwhentheatriaareinsystole,theventriclesareindiastole,andwhentheventriclesareinsystole,theatriaareindiastole.列精确的活动组成，这些活动使血液从静脉流过心脏最后再注入动脉。Youmaybeasking:allthisinoneheartbeat?Theanswerisyes.Thecardiaccycleisthisprecisesequenceofeventsthatkeepsbloodmovingfromtheveins,throughtheheartandintothearteries.7.心脏血液循环同时产生心:每一次心跳会有两个声音用听诊器可以听见。第一,最大也最长,是由心室收缩闭合房室瓣而引起的。第二声是由动脉和肺的半月瓣的闭合造成的。如果任一瓣膜闭合不全,就会听见另外一个声音，称为―心脏杂音‖。Thecardiaccyclealsocreatestheheartsounds:eachheartbeatproducestwosounds,whichcanbeheardwithastethoscope.Thefirstsound,theloudestandlongest,iscausedbyventricularsystoleclosingtheAVvalves.Thesecondsoundiscausedbytheclosureoftheaorticandpulmonarysemi-lunarvalves.Ifanyofthevalvesdonotcloseproperly,anextrasoundcalledaheartmurmurmaybeheard. 心脏的传导途径非由神经脉冲引起。心脏自行跳动，脑电脉冲沿一确定路径穿过心肌层。Thecardiaccycleisasequenceofmechanicaleventsthatisregulatedbytheelectricalactivityofthemyocardium.Cardiacmusclecellshavetheabilitytocontractspontaneously,thatis,nerveimpulsesarenotrequiredtocausecontraction.Theheartgeneratesitsownbeat,andtheelectricalimpulsesfollowaveryspecificroutethroughoutthemyocardium.心脏的自然起搏器是窦房结，它是位于右心房壁上的特化心肌细胞群。窦房结被认为是特化的是因为它有最快的收缩速度。Thenaturalpacemakeroftheheartisthesinoatrial(SA)node,aspecializedgroupofcardiacmusclecellslocatedinthewalloftherightatrium.TheSAnodeisconsideredspecializedbecauseithasthemostrapidrateofcontraction,thatis,itdepolarizesmorerapidlythananyotherpartofthemyocardium.收缩脉冲从窦房结运行到房室结，房室结位于心房间隔膜区下部。从窦房结和房室结到心房心肌层的其余部分的脉冲传导可引起心房收缩。FromtheSAnode,impulsesforcontractiontraveltotheatrioventricularnode,locatedinthelowerinteratrialseptum.ThetransmissionofimpulsesfromtheSAnodeandAVnodetotherestoftheatrialmyocardiumbringsaboutatrialsystole.它接收来自房室结的脉冲，并传给左右神经束支。脉冲从神经束支开始，沿着普肯野纤维到达心室心肌层的其他部分,并引起心室收缩。心电图可以显示心房和心室的电子活动。WithintheupperinterventricularseptumistheBundleofHis(AVbundle),whichreceivesimpulsesfromtheAVnodeandtransmitsthemtotherightandleftbundlebranches.Fromthebundlebranches,impulsestravelalongPurkinjefiberstotherestoftheventricularmyocardium,andbringaboutventricularsystole.Theelectricalactivityoftheatriaandventriclesisdepictedbyanelectrocardiogram(ECG)但速度较慢5060下1540下)是由心房到心室的脉冲传导被阻碍而引发IftheSAnodedoesnotfunctionproperly,theAVnodewillinitiatetheheartbeat,butataslowerrate(50to60beatsperminute).TheBundleofHisisalsocapableofgeneratingthebeatoftheventricles,butatamuchslowerrate(15to40beatsperminute).Thismayoccurincertain13.心率失常是不规则的心跳它们的影响范围小到对人体无害大到威而且可能是因为过多摄入了完全无法泵出血液的心室悸实Arrhythmiasareirregularheartbeats;theireffectsrangefromharmlesstolife-threatening.Nearlyeveryoneexperiencesheartpalpitationsfromtimetotime.Theseareusuallynotserious,andmaybetheresultoftoomuchcaffeine,nicotine,oralcohol.Muchmoreseriousisventricularfibrillation,averyrapidanduncoordinatedventricularbeatthatistotallyineffectiveforpumpingblood.心率6080下，是窦房结去极化的速度。一100120140物得到启示：老鼠的心率在每分钟200次左右，而大象的心率在每分钟30次左右。Ahealthyadulthasarestingheartrate(pulse)of60to80beatsperminute,whichistherateofdepolarizationoftheSAnode.Achildnrmalheartratemaybeashighas100beatsperminute,thatofaninfantashighas120,andthatofanear-termfetusashighas140beatsperminute.Thesehigherratesarenotrelatedtoage,butrathertosize:thesmallertheindividual,thehigherthemetabolicrateandthefastertheheartrate.Parallelsmaybefoundamonganimalsofdifferentsizes;theheartrateofamouseisabout200beatsperminute,andthatofanelephantabout30beatsperminute.让我们回到成人心率这个问题上来，设定一个人拥有良好的健康状况。正如你所知，一个身体状态良好的运动员的心率较低。那些篮球运动员的脉搏在每分钟50次左右，马拉松3540持续的运动使得心脏泵血更加有力。心 输 出 量Letusreturntotheadultheartrate,andconsiderthepersonwhoisinexcellentphysicalcondition.Asyoumayknow,well-conditionedathleteshavelowrestingpulserates.Thoseofbasketballplayersareoftenaround50beatsperminute,andthepulseofamarathonrunneroftenrangesfrom35to40beatsperminute.Tounderstandwhythisisso,rememberthattheheartisamuscle.Whenourskeletalmusclesareexercised,theybecomestrongerandmoreefficient.Thesameistruefortheheart;consistentexercisemakesitamoreefficientpump,asyouwillseeinthenextdiscussion.Cardiacoutputistheamountofbloodpumpedbyaventricleinoneminute.Acertainlevelofcardiacoutputisneededatalltimestotransportoxygentotissuesandtoremovewasteproducts.Duringexercise,cardiacoutputmustincreasetomeetthebody’sneedformoreoxygen.Wewillreturntoexerciseafterfirstconsideringrestingcardiacoutput.为了计算心输出量，我们必须知道心率和每次心跳所泵出的血液量。心脏供血量这一术60毫升。下面这个简单的公式能使我们很容易计算出心输出Inordertocalculatecardiacoutput,wemustknowthepulserateandhowmuchbloodispumpedperbeat.Strokevolumeisthetermfortheamountofbloodpumpedbyaventricleperbeat;anaveragerestingstrokevolumeis60to80mlperbeat.Asimpleformulathenenablesustodeterminecardiacoutput:Cardiacoutput＝Strokevolume×pulse(heartrate)我们假定人安静时的心室跳动一次的供血量为7070量＝70ml70bpm（每分钟脉搏次数）＝4900ml/m5L)Letusputintothisformulaanaveragerestingstrokevolume,70ml,andanaveragerestingpulse,70beatsperminute(bpm): Cardiacoutput＝70ml×70bpm Cardiactput＝4,900mlperminute (approximately5liters)当然心输出量的多少会随着人体型的大小而变，但人在静息状态下的心输出量是每分56升。Naturally,cardiacoutputvarieswiththesizeoftheperson,buttheaveragerestingcardiacoutputis5to6litersperminute.,550输出量＝5,000/50＝100每搏量Ifwenowreconsidertheathlete,youwillbeabletoseepreciselywhytheathletehasalowrestingpulse.Inourformula,wewilluseanaveragerestingcardiacoutput(5liters)andanathlete’spulserate(50):CardiacOutput＝Strokevolume×pulse 5,000/50＝Strokevolume 100mlStrokevolume我们注意到静息状态下运动员的心脏供血量明显高于常人。运动员的强有力的心脏每次跳动能为身体提供更多血液。因此，静息状态下他们保持一个较低的心率 。 Noticethattheathlete srestingstrokevolumeissignificantlyhigherthantheaverage.Theathlete’smoreefficientheartpumpsmorebloodwitheachbeat,andsocanmaintainanormalrestingcardiacoutputwithfewerbeats.现在我们再考虑一下心脏对运动作何反映。人在运动的过程中心率会加快，心输出量也心脏供血量的计算公式如下：kindsofheartdiseaseinwhichtransmissionofimpulsesfromtheatriatotheventriclesisblocked.心输出量＝每搏量×心率 心输出量＝100ml×100bpm心输出量＝10,000ml(10liters)Nowletusseehowtheheartrespondstoexercise.Heartrate(pulse)increasesduringexercise,andsodoesstrokevolume.TheincreaseinstrokevolumeistheresultofStarling’sLawoftheHeart,whichstatesthatthemorethecardiacmusclefibersarestretched,themoreforcefullytheycontract.Duringexercise,morebloodreturnstotheheart;thisiscalledvenousreturn.Increasedvenousreturnstretchesthemyocardiumoftheventricles,whichcontractmoreforcefullyandpumpmoreblood,therebyincreasingstrokevolume.Therefore,duringexercise,ourformulamightbethefollowing: Cardiacoutput ＝ Stroke×pulse Cardiacoutput＝100ml×100bpm Cardiacoutput＝10,000ml(10liters)一个健康年轻人每分钟的心输出量可以增加到他安静时的４倍Thisexercisecardiacoutputistwicetherestingcardiacoutputwefirstcalculated,whichshouldnotbeconsideredunusual.Thecardiacoutputofahealthyyoungpersonmayincreaseuptofourtimestherestinglevelduringstrenuousexercise.Thisexercisecardiacoutputistwicetherestingcardiacoutputwefirstcalculated,whichshouldnotbeconsideredunusual.Thecardiacoutputofahealthyyoungpersonmayincreaseuptofourtimestherestinglevelduringstrenuousexercise.心率的调节虽然心脏自行跳动并保持其跳动，但心脏收缩的频率可根据情况的不同而发生变化。神经系统可以调节心脏收缩的力度并控制心率的必要变Althoughtheheartgeneratesandmaintainsitsownbeat,therateofcontractioncanbechangedtoadapttodifferentsituations.Thenervoussystemcananddoesbringaboutnecessarychangesinheartrateaswellasinforceofcontraction.脑髓质有两个心血管控制中心：加速中枢和抑制中枢。两中枢通过自主神经向心脏传送过迷走神经传输到心脏，降低心脏跳动的速率。Themedullaofthebraincontainsthetwocardiaccenters,theacceleratorcenterandtheinhibitorycenter.Thesecenterssendimpulsestotheheartalongautonomicnerves.Theautonomicnervoussystemhastwodivisions:sympatheticandparasympathetic.Sympatheticimpulsesfromtheacceleratorcenteralongsympatheticnervesincreaseheartrateandforceofcontraction.Parasympatheticimpulsesfromtheinhibitorycenteralongthevagusnervesdecreasetheheartrate.我们下一个问题是脑髓质接受了什么信息才引起这些变化呢？既然心脏泵出血液，维持血液中含氧量的变化就会刺激心率产生相应的变化。Ournextquestionmightbe:whatinformationisreceivedbythemedullatoinitiatechanges?Sincetheheartpumpsblood,itisessentialtomaintainnormalbloodpressure.Bloodcontainsoxygen,whichalltissuesmustreceivecontinuously.Therefore,changesinbloodpressureandoxygenlevelofthebloodarestimuliforchangesinheartrate.心输出量＝每搏量×心率 心输出量＝100ml×100bpm心输出量＝10,000ml(10liters)Nowletusseehowtheheartrespondstoexercise.Heartrate(pulse)increasesduringexercise,andsodoesstrokevolume.TheincreaseinstrokevolumeistheresultofStarling’sLawoftheHeart,whichstatesthatthemorethecardiacmusclefibersarestretched,themoreforcefullytheycontract.Duringexercise,morebloodreturnstotheheart;thisiscalledvenousreturn.Increasedvenousreturnstretchesthemyocardiumoftheventricles,whichcontractmoreforcefullyandpumpmoreblood,therebyincreasingstrokevolume.Therefore,duringexercise,ourformulamightbethefollowing:Cardiacoutput＝Strokevolume×pulseCardiacoutput＝100ml×100bpmCardiacoutput＝10,000ml(10liters)一个健康年轻人每分钟的心输出量可以增加到他安静时的４倍Thisexercisecardiacoutputistwicetherestingcardiacoutputwefirstcalculated,whichshouldnotbeconsideredunusual.Thecardiacoutputofahealthyyoungpersonmayincreaseuptofourtimestherestinglevelduringstrenuousexercise.Thisexercisecardiacoutputistwicetherestingcardiacoutputwefirstcalculated,whichshouldnotbeconsideredunusual.Thecardiacoutputofahealthyyoungpersonmayincreaseuptofourtimestherestinglevelduringstrenuousexercise.心率的调节虽然心脏自行跳动并保持其跳动，但心脏收缩的频率可根据情况的不同而发生变化。神经系统可以调节心脏收缩的力度并控制心率的必要变Althoughtheheartgeneratesandmaintainsitsownbeat,therateofcontractioncanbechangedtoadapttodifferentsituations.Thenervoussystemcananddoesbringaboutnecessarychangesinheartrateaswellasinforceofcontraction.脑髓质有两个心血管控制中心：加速中枢和抑制中枢。两中枢通过自主神经向心脏传送过迷走神经传输到心脏，降低心脏跳动的速率。Themedullaofthebraincontainsthetwocardiaccenters,theacceleratorcenterandtheinhibitorycenter.Thesecenterssendimpulsestotheheartalongautonomicnerves.Theautonomicnervoussystemhastwodivisions:sympatheticandparasympathetic.Sympatheticimpulsesfromtheacceleratorcenteralongsympatheticnervesincreaseheartrateandforceofcontraction.Parasympatheticimpulsesfromtheinhibitorycenteralongthevagusnervesdecreasetheheartrate.我们下一个问题是脑髓质接受了什么信息才引起这些变化呢？既然心脏泵出血液，维持血液中含氧量的变化就会刺激心率产生相应化。Ournextquestionmightbe:whatinformationisreceivedbythemedullatoinitiatechanges?Sincetheheartpumpsblood,itisessentialtomaintainnormalbloodpressure.Bloodcontainsoxygen,whichalltissuesmustreceivecontinuously.Therefore,changesinbloodpressureandoxygenlevelofthebloodarestimuliforchangesinheartrate.压力感受器和化学受体位于颈动脉和主动脉弓。位于颈动脉窦和主动脉窦的压力感受器些事实集中在一个特例中，我们就可以看出心脏调节是一种反射。Pressoreceptorsandchemoreceptorsarelocatedinthecarotidarteriesandaorticarch.orsinthecarotidsinusesandaorticsinusdetectchangesinbloodpressure.Chemoreceptorsinthecarotidbodiesandaorticbodydetectchangesintheoxygencontentoftheblood.Thesensorynervesforthecarotidreceptorsaretheglossopharyngealnerves;thesensorynervesforaorticarchreceptorsarethevagusnerves.Ifwenowputallthesefactstogetherinaspecificexample,youwillseethattheregulationofheartrateisareflex.一个处于卧位的人突然变为站位，或许会感到一阵稍微的头晕，这是因为脑部血压突降这些副交感神经脉冲减缓心率至正常休息频率。Apersonwhostandsupsuddenlyfromalyingpositionmayfeellight-headedordizzyforafewmoments,becausebloodpressuretothebrainhasdecreasedabruptly.Thedropinbloodpressureisdetectedbypressoreceptorsinthecarotidnoticethattheyare“ontheway”tothebrain,averystrategiclocation.Impulsesgeneratedbythepressoreceptorstrav