藥學(xué)英語第五版原文翻譯

./IntroductiontoPhysiologyIntroductionPhysiologyisthestudyofthefunctionsoflivingmatter.Itisconcernedwithhowanorganismperformsitsvariedactivities:howitfeeds,howitmoves,howitadaptstochangingcircumstances,howitspawnsnewgenerations.Thesubjectisvastandembracesthewholeoflife.Thesuccessofphysiologyinexplaininghoworganismsperformtheirdailytasksisbasedonthenotionthattheyareintricateandexquisitemachineswhoseoperationisgovernedbythelawsofphysicsandchemistry.Althoughsomeprocessesaresimilaracrossthewholespectrumofbiology—thereplicationofthegeneticcodefororexample—manyarespecifictoparticulargroupsoforganisms.Forthisreasonitisnecessarytodividethesubjectintovariouspartssuchasbacterialphysiology,plantphysiology,andanimalphysiology.Tostudyhowananimalworksitisfirstnecessarytoknowhowitisbuilt.Afullappreciationofthephysiologyofanorganismmustthereforebebasedonasoundknowledgeofitsanatomy.Experimentscanthenbecarriedouttoestablishhowparticularpartsperformtheirfunctions.Althoughtherehavebeenmanyimportantphysiologicalinvestigationsonhumanvolunteers,theneedforprecisecontrolovertheexperimentalconditionshasmeantthatmuchofourpresentphysiologicalknowledgehasbeenderivedfromstudiesonotheranimalssuchasfrogs,rabbits,cats,anddogs.Whenitisclearthataspecificphysiologicalprocesshasacommonbasisinawidevarietyofanimalspecies,itisreasonabletoassumethatthesameprincipleswillapplytohumans.Theknowledgegainedfromthisapproachhasgivenusagreatinsightintohumanphysiologyandendoweduswithasolidfoundationfortheeffectivetreatmentofmanydiseases.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.Cellsdifferwidelyinformandfunctionbuttheyallhavecertaincommoncharacteristics.Firstly,theyareboundedbyalimitingmembrane,theplasmamembrane.Secondly,theyhavetheabilitytobreakdownlargemoleculestosmalleronestoliberateenergyfortheiractivities.Thirdly,atsomepointintheirlifehistory,theypossessanucleuswhichcontainsgeneticinformationintheformofdeoxyribonucleicacid<DNA>.Livingcellscontinuallytransformmaterials.Theybreakdownglucoseandfatstoprovideenergyforotheractivitiessuchasmotilityandthesynthesisofproteinsforgrowthandrepair.Thesechemicalchangesarecollectivelycalledmetabolism.Thebreakdownoflargemoleculestosmalleronesiscalledcatabolismandthesynthesisoflargemoleculesfromsmalleronesanabolism.Inthecourseofevolution,cellsbegantodifferentiatetoservedifferentfunctions.Somedevelopedtheabilitytocontract<musclecells>,otherstoconductelectricalsignals<nervecells>.Afurthergroupdevelopedtheabilitytosecretedifferentsubstancessuchashormonesorenzymes.Duringembryologicaldevelopment,thisprocessofdifferentiationisre-enactedasmanydifferenttypesofcellareformedfromthefertilizedegg.Mosttissuescontainamixtureofcelltypes.Forexample,bloodconsistsofredcells,whitecells,andplatelets.Redcellstransportoxygenaroundthebody.Thewhitecellsplayanimportantroleindefenseagainstinfectionandtheplateletsarevitalcomponentsintheprocessofbloodclotting.Thereareanumberofdifferenttypesofconnectivetissuebutallarecharacterizedbyhavingcellsdistributedwithinanextensivenoncellularmatrix.Nervetissuecontainsnervecellsandglialcells.ThePrincipalOrganSystemsThecardiovascularsystemThecellsoflargemulticellularanimalscannotderivetheoxygenandnutrientstheyneeddirectlyfromtheexternalenvironment.Theoxygenandnutrientsmustbetransportedtothecells.Thisisoneoftheprincipalfunctionsoftheblood,whichcirculateswithinbloodvesselsbyvirtueofthepumpingactionoftheheart.Theheart,bloodvessels,andassociatedtissuesformthecardiovascularsystem.Theheartconsistsoffourchambers,twoatriaandtwoventricles,whichformapairofpumpsarrangedsidebyside.Therightventriclepumpsdeoxygenatedbloodtothelungswhereitabsorbsoxygenfromtheair,whiletheleftventriclepumpsoxygenatedbloodreturningfromthelungstotherestofbodytosupplythetissues.Physiologistsareconcernedwithestablishingthefactorsresponsiblefortheheartbeat,howtheheartpumpsthebloodaroundthecirculation,andhowitisdistributedtoperfusethetissuesaccordingtotheirneeds.Fluidexchangedbetweenthebloodplasmaandthetissuespassesintothelymphaticsystem,whicheventuallydrainsbackintotheblood.TherespiratorysystemTheenergyrequiredforperformingthevariousactivitiesofthebodyisultimatelyderivedfromrespiration.Thisprocessinvolvestheoxidationoffoodstuffstoreleasetheenergytheycontain.Theoxygenneededforthisprocessisabsorbedfromtheairinthelungsandcarriedtothetissuesbytheblood.Thecarbondioxideproducedbytherespiratoryactivityofthetissuesiscarriedtothelungsbythebloodinthepulmonaryarterywhereitisexcretedintheexpiredair.Thebasicquestionstobeansweredincludethefollowing:Howistheairmovedinandoutofthelungs?Howisthevolumeofairbreathedadjustedtomeettherequirementsofthebody?Whatlimitstherateofoxygenuptakeinthelungs?ThedigestivesystemThenutrientsneededbythebodyarederivedfromthediet.Foodistakeninbythemouthandbrokendownintoitscomponentpartsbyenzymesinthegastrointestinaltract.Thedigestiveproductsarethenabsorbedintothebloodacrossthewalloftheintestineandpasstotheliverviatheportalvein.Thelivermakesnutrientsavailabletothetissuesbothfortheirgrowthandrepairandfortheproductionofenergy.Inthecaseofthedigestivesystem,keyphysiologicalquestionsare:Howisfoodingested?Howisitbrokendownanddigested?Howaretheindividualnutrientsabsorbed?Howisthefoodmovedthroughthegut?Howaretheindigestibleremainseliminatedfromthebody?ThekidneysandurinarytractThechieffunctionofthekidneysistocontrolthecompositionoftheextracellularfluid.Inthecourseofthisprocess,theyalsoeliminatenon-volatilewasteproductsfromtheblood.Toperformthesefunctions,thekidneysproduceurineofvariablecompositionwhichistemporarilystoredinthebladderbeforevoiding.Thekeyphysiologicalquestionsinthiscaseare:howdothekidneysregulatethecompositionoftheblood?Howdotheyeliminatetoxicwaste?Howdotheyrespondtostressessuchasdehydration?Whatmechanismsallowthestorageandeliminationoftheurine?ThereproductivesystemReproductionisoneofthefundamentalcharacteristicsoflivingorganisms.Thegonadsproducespecializedsexcellsknownasgametes.Atthecoreofsexualreproductionisthecreationandfusionofthemaleandfemalegametes,thespermandova<eggs>,withtheresultthatthegeneticcharacteristicsoftwoseparateindividualsaremixedtoproduceoffspringthatdiffergeneticallyfromtheirparents.ThemusculoskeletalsystemThisconsistsofthebonesoftheskeleton,skeletalmuscles,joints,andtheirassociatedtissues.Itsprimaryfunctionistoprovideameansofmovement,whichisrequiredforlocomotion,forthemaintenanceofposture,andforbreathing.Italsoprovidesphysicalsupportfortheinternalorgans.Herethemechanismofmusclecontractionisacentralissue.Theendocrineandnervoussystems.TheendocrineandnervoussystemsTheactivitiesofthedifferentorgansystemsneedtobecoordinatedandregulatedsothattheyacttogethertomeettheneedsofthebody.Twocoordinatingsystemshaveevolved:thenervoussystemandtheendocrinesystem.Thenervoussystemuseselectricalsignalstotransmitinformationveryrapidlytospecificcells.Thusthenervespasselectricalsignalstotheskeletalmusclestocontroltheircontraction.Theendocrinesystemsecreteschemicalagents,hormones,whichtravelinthebloodstreamtothecellsuponwhichtheyexertaregulatoryeffect.Hormonesplayamajorroleintheregulationofmanydifferentorgansandareparticularlyimportantintheregulationofthemenstrualcycleandotheraspectsofreproduction.Theimmunesystemprovidesthebody’sdefensesagainstinfectionbothbykillinginvadingorganismsandbyeliminatingdiseasedordamagedcells.Althoughitishelpfultostudyhoweachorganperformsitsfunctions,itisessentialtorecognizethattheactivityofthebodyasawholeisdependentontheintricateinteractionsbetweenthevariousorgansystems.Ifonepartfails,theconsequencesarefoundinotherorgansystemsthroughoutthewholebody.Forexample,ifthekidneysbegintofail,theregulationoftheinternalenvironmentisimpairedwhichinturnleadstodisordersoffunctionelsewhere.HomeostasisComplexmechanismsareatworktoregulatethecompositionoftheextracellularfluidandindividualcellshavetheirownmechanismsforregulatingtheirinternalcomposition.Theregulatorymechanismsstabilizetheinternalenvironmentdespitevariationsinboththeexternalworldandtheactivityoftheanimal.Theprocessofstabilizationoftheinternalenvironmentiscalledhomeostasisandisessentialifthecellsofthebodyaretofunctionnormally.Takingoneexample,thebeatingoftheheartdependsontherhythmicalcontractionsofcardiacmusclecells.Thisactivitydependsonelectricalsignalswhich,inturn,dependontheconcentrationofsodiumandpotassiumionsintheextracellularandintracellularfluids.Ifthereisanexcessofpotassiumintheextracellularfluid,thecardiacmusclecellsbecometooexcitableandmaycontractatinappropriatetimesratherthaninacoordinatedmanner.Consequently,theconcentrationofpotassiumintheextracellularfluidmustbekeptwithinanarrowrangeiftheheartistobeatnormally.HowDoesTheBodyRegulateItsOwnComposition?TheconceptofbalanceInthecourseofaday,anadultconsumesapproximately1kgoffoodanddrinks2~3litersoffluid.Inamonth,thisisequivalenttoaround30kgoffoodand60~90litersoffluid.Yet,ingeneral,bodyweightremainsremarkablyconstant.Suchindividualsaresaidtobeinbalance;theintakeoffoodanddrinkmatchestheamountsusedtogenerateenergyfornormalbodilyactivitiesplusthelossesinurineandfeces.Insomecircumstances,suchasstarvation,intakedoesnotmatchtheneedsofthebodyandmuscletissueisbrokendowntoprovideglucoseforthegenerationofenergy.Here,theintakeofproteinislessthantherateofbreakdownandtheindividualissaidtohaveanegativenitrogenbalance.Equally,ifthebodytissuesarebeingbuiltup,asisthecaseforgrowingchildren,pregnantwomenandathletesintheearlystagesoftraining,thedailyintakeofproteinisgreaterthanthenormalbodyturnoverandtheindividualisinpositivenitrogenbalance.Thisconceptofbalancecanbeappliedtoanyofthebodyconstituentsincludingwaterandsaltandisimportantinconsideringhowthebodyregulatesitsowncomposition.Intakemustmatchrequirementsandanyexcessmustbeexcretedforbalancetobemaintained.Additionally,foreachchemicalconstituentofthebodythereisadesirableconcentrationrange,whichthecontrolmechanismsareadaptedtomaintain.Forexample,theconcentrationofglucoseintheplasmaisabout4~5mmol/Lbetweenmeals.Shortlyafterameal,plasmaglucoserisesabovethislevelandthisstimulatesthesecretionofthehormoneinsulinbythepancreas,whichactstobringtheconcentrationdown.Astheconcentrationofglucosefalls,sodoesthesecretionofinsulin.Ineachcase,thechangesinthecirculatinglevelofinsulinacttomaintaintheplasmaglucoseatanappropriatelevel.Thistypeofregulationisknownasnegativefeedback.Duringtheperiodofinsulinsecretion,theglucoseisbeingstoredaseitherglycogenorfat.Anegativefeedbackloopisacontrolsystemthatactstomaintainthelevelofsomevariablewithinagivenrangefollowingadisturbance.Althoughtheexamplegivenabovereferstoplasmaglucose,thebasicprinciplecanbeappliedtootherphysiologicalvariablessuchasbodytemperature,bloodpressure,andtheosmolalityoftheplasma.Anegativefeedbacklooprequiresasensorofsomekindthatrespondstothevariableinquestionbutnottootherphysiologicalvariables.Thusanosmoreceptorshouldrespondtochangesinosmolalityofthebodyfluidsbutnottochangesinbodytemperatureorbloodpressure.theinformationfromthesensormustbecomparedinsomewaywiththedesiredlevelbysomeformofcomparator.ifthetwodonotmatch,anerrorsignalistransmittedtoaneffector,asystemthatcanacttorestorethevariabletoitsdesiredlevel.thesefeaturesofnegativefeedbackcanbeappreciatedbyexaminingasimpleheatingsystem.thecontrolledvariableisroomtemperature,whichissensedbyathermostat.theeffectorisaheaterofsomekind.whentheroomtemperaturefallsbelowthesetpoint,thetemperaturedifferenceisdetectedbythethermostatwhichswitchesontheheater.thisheatstheroomuntilthetemperaturereachesthepersetlevelwhereupontheheaterisswitchedoff.Tosummarize,thebodyisactuallyasocialorderofabout100trillioncellsorganizedintodifferentfunctionalstructures,someofwhicharecalledorgans.eachfunctionalstructuresitssharetothemaintenanceofhomeostaticconditionsintheextracellularfluid,whichiscalledtheinternalenvironment.aslongasnormalconditionsaremaintainedinthisinternalenvironment,thecellsofthebodycontinuetoliveandfunctionproperly.Eachcellbenefitsfromhomeostasis,andinturn,eachcellcontributesitssharetowardthemaintenanceofhomeostasis.Thisreciprocalinterplayprovidescontinuousautomaticityofthebodyuntiloneormorefunctionalsystemslosetheirabilitytocontributetheirshareoffunction.Whenthishappens,allthecellsofthebodysuffer.Extremedysfunctionleadstodeath;moderatedysfunctionleadstosickness.生理學(xué)簡(jiǎn)介介紹生理學(xué)是研究生物體功能的科學(xué).它研究生物體如何進(jìn)行各種活動(dòng),如何飲食,如何運(yùn)動(dòng),如何適應(yīng)不斷改變的環(huán)境,如何繁殖后代.這門學(xué)科包羅萬象,涵蓋了生物體整個(gè)生命過程.生理學(xué)成功地解釋了生物體如何進(jìn)行日?；顒?dòng),基于的觀點(diǎn)是生物體好比是結(jié)構(gòu)復(fù)雜而靈巧的機(jī)器,其操作受物理和化學(xué)規(guī)律控制.盡管從生物學(xué)整個(gè)范疇看,生物體某些活動(dòng)過程是相似的——如基因編碼的復(fù)制——但許多過程還是某些生物體群組特有的.鑒于此有必要將這門學(xué)科分成不同部分研究,如細(xì)菌生理學(xué)、植物生理學(xué)和動(dòng)物生理學(xué).要研究一種動(dòng)物如何活動(dòng),首先需要了解它的構(gòu)成.要充分了解一個(gè)生物體的生理學(xué)活動(dòng)就必須掌握全面的解剖學(xué)知識(shí).一個(gè)生物體的各部分起著什么作用可通過實(shí)驗(yàn)觀察得知.盡管我們對(duì)志愿者進(jìn)行了許多重要的生理調(diào)查,但是實(shí)驗(yàn)條件需要精確控制,所以我們當(dāng)前大多生理知識(shí)還是源于對(duì)其它動(dòng)物如青蛙,兔子,貓和狗等的研究.當(dāng)我們明確大多數(shù)動(dòng)物物種的特定生理過程存在共同之處時(shí),相同的生理原理適用于人類也是合理的.通過這種方法,我們獲得了大量的知識(shí),從而讓我們對(duì)人類生理學(xué)有了更深入的了解,為我們有效治療許多疾病提供了一個(gè)堅(jiān)實(shí)的基礎(chǔ).機(jī)體的基本組成物質(zhì)是細(xì)胞,細(xì)胞結(jié)合在一起形成組織.組織的基本類型有上皮組織,結(jié)締組織,神經(jīng)組織和肌組織,每類組織都有各自的特征.許多結(jié)締組織中細(xì)胞量相對(duì)較少,但是有大量的細(xì)胞外基質(zhì).相比而言,光滑的肌組織由大量密密麻麻的肌細(xì)胞通過特定的細(xì)胞連接組成.各種器官如腦,心臟,肺,小腸和肝等由不同種類的組織聚集而成.這些器官是不同生理系統(tǒng)的組成部分.心臟和血管組成心血管系統(tǒng)；肺,器官,支氣管,胸壁和膈肌組成呼吸系統(tǒng)；骨骼和骨骼肌組成骨骼肌系統(tǒng)；大腦,脊髓,自主神經(jīng)和神經(jīng)中樞以及周圍軀體神經(jīng)組成神經(jīng)系統(tǒng)等等.細(xì)胞在形體和功能上差異很大,但是它們有某些共同的特征.第一,它們由限制膜包被,即細(xì)胞質(zhì)膜；第二,細(xì)胞有把大分子分解為小分子來釋放活動(dòng)所需能量的能力；第三,在生命過程中某個(gè)階段,細(xì)胞體內(nèi)存在一個(gè)以脫氧核糖核酸<DNA>形式包含基因信息的細(xì)胞核.活體細(xì)胞不斷轉(zhuǎn)化物質(zhì).它們?yōu)槠渌顒?dòng)提供能量分解葡萄糖和脂肪,比如自身生長(zhǎng)和修復(fù)所需的蛋白質(zhì)運(yùn)動(dòng)和合成.這些化學(xué)變化統(tǒng)稱為新陳代謝.把大分子分解為小分子的過程稱為分解代謝,小分子合成大分子的過程稱為合成代謝.細(xì)胞在進(jìn)化過程中不斷分化進(jìn)行不同的功能活動(dòng).有些細(xì)胞具有收縮能力〔如肌細(xì)胞,有些可以傳導(dǎo)電信號(hào)〔如神經(jīng)細(xì)胞.進(jìn)一步進(jìn)化的細(xì)胞能夠分泌不同物質(zhì)如荷爾蒙〔如內(nèi)分泌細(xì)胞或酶.胚胎發(fā)育過程中,分化的過程由于很多不同細(xì)胞來源于受精卵而再次發(fā)生.大多數(shù)組織包含有不同的細(xì)胞類型.比如,血液中含紅細(xì)胞,白細(xì)胞和血小板.紅細(xì)胞運(yùn)輸全身的氧氣.白細(xì)胞在抵御感染時(shí)起重要作用,血小板是血液凝集過程中重要的成分.結(jié)締組織有多種不同類型,但有一個(gè)共同特征,即細(xì)胞分布在豐富的細(xì)胞外基質(zhì)中.神經(jīng)組織含神經(jīng)細(xì)胞和神經(jīng)膠質(zhì)細(xì)胞.主要的器官系統(tǒng)心血管系統(tǒng)大型多細(xì)胞動(dòng)物體的細(xì)胞不能從外界環(huán)境中獲取直接所需的氧氣和營(yíng)養(yǎng)物質(zhì).這些氧氣和營(yíng)養(yǎng)物質(zhì)必須轉(zhuǎn)運(yùn)到細(xì)胞.這是血液的主要功能之一,血液憑借心臟的泵血作用在血管內(nèi)流動(dòng)循環(huán).心臟、血管和結(jié)締組織組成了心血管系統(tǒng).心臟包括四個(gè)腔,兩個(gè)心房和兩個(gè)心室構(gòu)成了一對(duì)并排存在的泵.右心室將脫氧的血液泵至肺中,肺中的血液吸收空氣中的氧氣,而左心室把從肺回流來的有氧血液泵出至身體其它部位,供應(yīng)給各組織.生理學(xué)家研究促使心臟跳動(dòng)的因素,心臟如何泵送血液使其循環(huán),心臟如何根據(jù)各組織所需分配血液.血漿和組織間的流動(dòng)液體交換流入淋巴系統(tǒng),最終回流到血液中.呼吸系統(tǒng)機(jī)體進(jìn)行各項(xiàng)活動(dòng)所需的能量最終來源于呼吸.這一過程包括食物〔主要是糖類和脂肪的氧化,釋放它們所含的能量.這一過程中,氧氣來自于肺中的空氣,經(jīng)由血液到達(dá)全身各組織.組織呼吸活動(dòng)中釋放的二氧化碳由肺動(dòng)脈中的血液運(yùn)送至肺,然后呼氣排出體外.需回答的基本問題如下：空氣是如何進(jìn)出肺的？呼吸的空氣量如何適應(yīng)機(jī)體所需？限制肺吸收氧氣頻率的因素是什么？消化系統(tǒng)機(jī)體所需營(yíng)養(yǎng)物質(zhì)來源于飲食.食物經(jīng)口腔進(jìn)入體內(nèi),在胃腸道內(nèi)經(jīng)酶將其分解成小分子物質(zhì).這些消化物通過腸壁吸收入血液,通過門靜脈進(jìn)入肝臟.經(jīng)肝臟作用后,這些營(yíng)養(yǎng)物質(zhì)能夠滿足組織生長(zhǎng)修復(fù)及能量需求.在消化系統(tǒng)部分,重要的生理學(xué)問題是：食物是如何消化的？食物如何被個(gè)體分解消化？個(gè)體營(yíng)養(yǎng)物質(zhì)如何吸收？食物如何在腸內(nèi)轉(zhuǎn)運(yùn)的？未消化的殘留如何從體內(nèi)排出？泌尿系統(tǒng)腎臟主要功能是控制細(xì)胞外液體的形成.在這一過程中,腎臟也會(huì)把不可揮發(fā)的廢物排出去.為行使這一功能,在排出之前,腎臟產(chǎn)生含有各種成分的尿液并將其暫時(shí)儲(chǔ)存在膀胱中.這一部分主要的生理學(xué)問題是：腎臟如何調(diào)節(jié)血液中的成分？如何排出有毒廢物？如何應(yīng)對(duì)像脫水這樣的應(yīng)激反應(yīng)？以及尿液可以存儲(chǔ)和排出體外的機(jī)制是什么？生殖系統(tǒng)生殖是活生物體的一個(gè)基本特征.生殖腺產(chǎn)生專門的性細(xì)胞,被稱為配子.性生殖的核心是雌雄配子即精子和卵子的產(chǎn)生和融合,因此兩個(gè)獨(dú)立個(gè)體的基因特征融合而產(chǎn)生一個(gè)基因上與雙親不同的后代.運(yùn)動(dòng)系統(tǒng)這一系統(tǒng)由骨、骨骼肌、關(guān)節(jié)和它們的相關(guān)組織組成.其主要功能是提供運(yùn)動(dòng)需要,維持姿勢(shì)及呼吸運(yùn)動(dòng).它也為內(nèi)臟器官提供物理支持.這一部分,肌肉收縮機(jī)制是主要問題.內(nèi)分泌系統(tǒng)和神經(jīng)系統(tǒng)不同器官系統(tǒng)的活動(dòng)需要協(xié)作和調(diào)節(jié),以便共同作用滿足機(jī)體需要.人體有兩大調(diào)節(jié)系統(tǒng)：神經(jīng)系統(tǒng)和內(nèi)分泌系統(tǒng).神經(jīng)系統(tǒng)通過電信號(hào)迅速將信息傳導(dǎo)給特定細(xì)胞.這樣神經(jīng)將電信號(hào)傳遞給骨骼肌以控制收縮.內(nèi)分泌系統(tǒng)分泌化學(xué)物質(zhì)―激素.激素通過血流到達(dá)施與調(diào)節(jié)作用的細(xì)胞.激素在許多不同器官中起著重要作用,在月經(jīng)期調(diào)節(jié)和其它生殖方面尤其重要.免疫系統(tǒng)通過殺死入侵的有機(jī)體,清除致病或損傷細(xì)胞為機(jī)體提供防御功能.雖然研究各器官如何行使功能很有益處,但我們必須認(rèn)識(shí)到機(jī)體作為一個(gè)整體所做的活動(dòng)依賴于各器官系統(tǒng)間錯(cuò)綜復(fù)雜的相互作用.如果一部分無法正常工作,全身其它器官系統(tǒng)也會(huì)受到影響.例如,如果腎臟出現(xiàn)問題,內(nèi)部環(huán)境的調(diào)節(jié)受損,結(jié)果導(dǎo)致其它器官系統(tǒng)功能紊亂.穩(wěn)態(tài)各種復(fù)雜機(jī)制共同作用調(diào)節(jié)細(xì)胞外液的形成,不同個(gè)體細(xì)胞有自身機(jī)制調(diào)節(jié)內(nèi)在組成成分.盡管外界環(huán)境和動(dòng)物活動(dòng)不停變化,調(diào)節(jié)機(jī)制維持著體內(nèi)環(huán)境的穩(wěn)定.內(nèi)部環(huán)境的穩(wěn)定被稱為穩(wěn)態(tài),它是機(jī)體能夠正常發(fā)揮作用所必須的.例如,心臟的跳動(dòng)依賴于心肌細(xì)胞有節(jié)律的收縮.這一活動(dòng)依賴于電信號(hào),而電信號(hào)反過來依賴存在于細(xì)胞外和細(xì)胞內(nèi)液體中鈉和鉀離子的濃度.如果細(xì)胞外液中鉀離子過多,心肌細(xì)胞興奮性增強(qiáng),可能出現(xiàn)不規(guī)律的收縮.因此,要維持心臟正常跳動(dòng),細(xì)胞外液中鉀離子的濃度就必須控制在一定范圍內(nèi).機(jī)體如何調(diào)節(jié)物質(zhì)成分平衡的概念一天中,一個(gè)成人需要消耗約1千克食物,2~3升液體.以一個(gè)月計(jì)算,這相當(dāng)于約30千克食物,60~90升液體.然而,一般來說,機(jī)體體重是基本不變的.這類個(gè)體可以說處于平衡狀態(tài).食物和液體的攝入量相當(dāng)于正常機(jī)體活動(dòng)消耗的能量加上尿液和糞便中丟失的能量.在一些情況下,如饑餓狀態(tài),攝入量與機(jī)體所需量并不相當(dāng),肌組織斷裂,提供葡萄糖產(chǎn)生能量.蛋白質(zhì)的攝入低于肌組織斷裂的速度,機(jī)體處于負(fù)氮平衡.同樣地,如果機(jī)體組織正處于生長(zhǎng)期,如生長(zhǎng)期的兒童,孕婦和早期訓(xùn)練階段的運(yùn)動(dòng)員,那么蛋白質(zhì)的日常攝入量比正常機(jī)體所需要的多.相反,此時(shí)個(gè)體處于正氮平衡.平衡的概念可以應(yīng)用到機(jī)體的任何構(gòu)成成分上,包括水和鹽,而且平衡在機(jī)體調(diào)節(jié)其自身成分上是非常重要的.攝入必須等于所需,為維持機(jī)體平衡,任何多余的能量都必須排出.此外,因?yàn)闄C(jī)體的每種化學(xué)成分都有一個(gè)可取的濃度范圍,控制機(jī)制維持這個(gè)范圍.例如,兩餐間血糖濃度大約為4~5mmol/L.進(jìn)食后不久,血糖含量超過這一范圍,刺激胰腺分泌胰島素,降低濃度.隨著葡萄糖濃度的下降,胰島素分泌減少.在此情況下,循環(huán)胰島素水平的改變都是為了使血漿中的葡萄糖維持在一個(gè)合適的范圍內(nèi).這種調(diào)節(jié)稱為負(fù)反饋機(jī)制.在胰島素分泌期間,葡萄糖像肝糖原或脂肪一樣被儲(chǔ)存.負(fù)反饋調(diào)節(jié)是在機(jī)體出現(xiàn)紊亂時(shí),將一些變量控制在限定范圍內(nèi)的一個(gè)控制系統(tǒng).雖然上面的例子講到血糖,但這一基本原則可以應(yīng)用到其它生理變量中如體溫、血壓和血漿的滲透濃度.負(fù)反饋調(diào)節(jié)需要一種能對(duì)不確定的變量做出反應(yīng)而對(duì)其它生理變量不應(yīng)答的傳感器.因此,滲透壓感受器應(yīng)該能對(duì)機(jī)體體液滲透的變化而不是體溫和血壓的變化產(chǎn)生應(yīng)答.感受器傳遞的信息必須和理想水平〔系統(tǒng)的調(diào)定點(diǎn)以比較者的身份,以某種方式進(jìn)行比較.如果兩者不相符,一個(gè)錯(cuò)誤信號(hào)就會(huì)傳遞給效應(yīng)器,效應(yīng)器是一種能使變量保持在理想水平的系統(tǒng).負(fù)反饋的這些特點(diǎn)可以通過檢測(cè)一種簡(jiǎn)單的加熱系統(tǒng)來理解.被控制的變量是室溫,它可以由一個(gè)溫度計(jì)檢測(cè)到,效應(yīng)器是一種加熱器.當(dāng)室溫降低到調(diào)定點(diǎn)以下時(shí),溫度計(jì)就可以監(jiān)測(cè)到溫度的變化而開啟加熱器,對(duì)室內(nèi)進(jìn)行加溫,直到室溫升高到先前調(diào)好的調(diào)定點(diǎn),加熱器關(guān)閉.總而言之,機(jī)體實(shí)際上是由100萬億細(xì)胞有序組成了不同的功能結(jié)構(gòu),其中一些被稱為器官.每個(gè)功能結(jié)構(gòu)都在維持細(xì)胞外液穩(wěn)態(tài)方面發(fā)揮其作用,這稱之為內(nèi)環(huán)境.只要內(nèi)部環(huán)境處于正常狀態(tài),機(jī)體細(xì)胞繼續(xù)生存并正常運(yùn)行.每個(gè)細(xì)胞都從穩(wěn)態(tài)中獲益,反過來,每個(gè)細(xì)胞都為穩(wěn)態(tài)做出貢獻(xiàn).這種相互作用促使機(jī)體持續(xù)自主運(yùn)行,直至一個(gè)或多個(gè)功能系統(tǒng)不能正常運(yùn)轉(zhuǎn).此時(shí),機(jī)體所有細(xì)胞都會(huì)受損.功能極度異常會(huì)導(dǎo)致死亡,輕微的功能異常導(dǎo)致疾病的發(fā)生.TheOtherSideofAntibioticsAntibioticshaveeliminatedorcontrolledsomanyinfectiousdiseasesthatvirtuallyeveryonehasbenefitedfromtheir

useatonetimeoranother.Evenwithoutsuchpersonalexperience,however,onewouldhavetobeisolatedindeedtobe

unawareofthevirtues,realandspeculative,ofthese"miracle"drugs.TheAmericanpress,radio,andtelevisionhave

doneagoodjobofreportingthetrulyremarkablestoryofsuccessesinthechemicalwarongerms.What’smore,any

shortcomingsontheirparthavebeenmorethanmadeupforbytheaggressivepublicrelationsactivityofthepharmaceutical

companieswhichmanufactureandsellantibiotics.Incomparison,theinadequaciesandpotentialdangersoftheseremarkabledrugsaremuchlesswidelyknown.Andthelack

ofsuchknowledgecanbebad,especiallyifitleadspatientstopressuretheirdoctorsintoprescribingantibioticswhen

suchmedicationisn’treallyneeded,orleadsthemtoswitchdoctorsuntiltheyfindonewhois,sotospeak,

antibiotics-minded.Becausethegoodsideoftheantibioticsstoryissoverywell-known,thereseemsmorepointheretoareviewofsomeof

theimmediateandlong-rangeproblemsthatcancomefromtoday’scasualuseofthesedrugs.Itshouldbemadeclearin

advancethatcalamitiesfromtheuseofantibioticsarerareinrelationtotheenormousamountsofthedrugsadministered.Butthepotentialhazards,solittletouchedongenerally,doneedaclearstatement.Theantibioticsarenot,strictly

speaking,exclusivelyprescriptiondrugs.Anumberofthemarepermittedinsuchover-the-counterproductsasnasalsprays,

lozenges,troches,creams,andointments.Eveniftheseproductsdonoharm,thereisnopointwhatsoeverinusingthem.If

youhaveaninfectionseriousenoughtowarrantthelaunchingofchemicalwarfare,youneedmuchbiggerdosesofthe

antibioticsthananyofthenon-prescriptionproductsareallowedtocontain.Over-the-counterproducts,however,accountforonlyasmallpercentageoftotalantibioticsproduction.Itisthe

prescriptiondosagesthatgivepeopletrouble.Thesedrugs—evenallowingforthediverseabilitiesofthemany

narrow-spectrumonesandtheversatilityofthebroad-spectrumones—arenotthecure-alls,theyoftenarebilledasbeing.Therearewidegapsintheirabilitytomastercontagiousdiseases.Suchimportantinfectionsasmumps,measles,commoncolds,

influenza,andinfectioushepatitisstillawaitconquest.Allarevirusinfectionsanddespiteintenseefforts,verylittle

progresshasbeenmadeinchemotherapyagainstviruses.Onlysmallprogresshasbeenachievedagainstfungi.Manystrainsof

bacteriaandfungiarenaturallyresistanttoallcurrentlyavailableantibioticsandotherchemotherapeuticdrugs.Some

microorganismsoriginallysensitivetotheactionofantibiotics,especiallystaphylococcus,havedevelopedresistantstrains.Thisacquiredresistanceimposesonthelongrangevalueofthedrugsaveryimportantlimitation,whichisnotadequately

metbythefrequentintroductionofnewantimicrobialagentstocombattheproblem.Ithasbeenprettywellestablishedthattheincreaseinstrainsofbacteriaresistanttoanantibioticcorrelates

directlywiththedurationandextentofuseofthatantibioticinagivenlocation.Inonehospitalasurveyshowedthat,

beforeerythromycinhadbeenwidelyusedthere,allstrainsofstaphylococcitakenfrompatientsandpersonnelwere

sensitivetoitsaction.Whenthehospitalstartedextensiveuseoferythromycin,however,resistantstaphylococcusstrains

begantoappear.Thedevelopmentofbacterialresistancecanbeminimizedbyamorediscriminatinguseofantibiotics,andtheperson

takingthedrugcanhelphere.Whenanantibioticmustbeused,thebestwaytopreventthedevelopmentofresistanceisto

wipeouttheinfectionasrapidlyandthoroughlyaspossible.Ideally,thisrequiresabactericidaldrug,whichdestroys,

ratherthanabacteriostaticdrug,whichinhibits.Andthedrugmustbetakeninadequatedosageforaslongasitis

necessarytoeradicatetheinfectioncompletely.Thedoctor,ofcourse,mustchoosethedrug,butpatientscanhelpbybeing

suretotakethefullcourseoftreatmentrecommendedbythedoctor,eventhoughsymptomsseemtodisappearbeforeallthe

pillsaregone.Inrareinstancestheemergenceofresistancecanbedelayedorreducedbycombinationsofantibiotics.Treatmentoftuberculosiswithstreptomycinaloneresultsinahighdegreeofresistance,butifpara-aminosalicylicacidor

isoniazidisusedwithstreptomycinthepossibilitythatthiscomplicationwillariseisgreatlyreduced.Inhospitaltreatmentofsevereinfections,thesensitivityoftheinfectingorganismtoappropriateantibioticsis

determinedinthelaboratorybeforetreatmentisstarted.Thisenablesthedoctortoselectthemosteffectivedrugordrugs;

itdetermineswhethertheantibioticisbactericidalorbacteriostaticforthegermsathand;anditsuggeststheamount

neededtodestroythegrowthofthebacteriacompletely.Ineitherhospitalorhome,asepticmeasurescanhelptoreducethe

prevalenceofresistantstrainsofgermsbypreventingcrossinfectionandtheresultantspreadingoforganisms.Everyoneoftheantibioticsispotentiallydangerousforsomepeople.Severalseriousreactionsmayresultfromtheir

use.Oneisasevere,sometimesfatal,shock-likeanaphylacticaction,whichmaystrikepeoplewhohavebecomesensitizedto

penicillin.Anaphylacticreactionhappenslessfrequentlyandislessseverewhentheantibioticisgivenbymouth.Itis

mostapttooccurinpeoplewithahistoryofallergy,orarecordofsensitivitytopenicillin.Verysmallamountsof

penicillin,eventhetraceswhichgetintothemilkofcowsforafewdaysaftertheyaretreatedwiththeantibioticfor

mastitis,maybesufficienttosensitize;hence,thestrongcampaignbyfoodanddrugofficialskeepssuchmilkoffthe

market.Tominimizetheriskofanaphylacticshockinillnesseswhereinjectionsofpenicillinarethepreferredtreatment,a

carefuldoctorwillquestionthepatientcarefullyaboutallergiesandpreviousreactions.Incaseofdoubtanother

antibioticwillbesubstitutediffeasible,orotherprecautionarymeasureswillbetakenbeforetheinjectionisgiven.Otheruntowardreactionstoantibioticsaregastrointestinaldisorders—suchassoremouth,cramps,diarrhea,oranal

itch—whichoccurmostfrequentlyafteruseofthetetracyclinegroupbuthavealsobeenencounteredafteruseofpenicillin

andstreptomycin.Thesereactionsmayresultfromsuppressionbytheantibioticofbacterianormallyfoundinthe

gastrointestinaltract.Withtheircompetitionremoved,antibiotic-resistantstaphylococciorfungi,whicharealsonormally

present,arefreetoflourishandcausewhatiscalledasuper-infection.Suchinfectionscanbeextremelydifficulttocure.Afewantibioticshavesuchtoxiceffectsthattheirusefulnessisstrictlylimited.Theyincludestreptomycinand

dihydrostreptomycin,whichsometimescausedeafness,andchloramphenicol,whichmayinjurethebonemarrow.Drugswithsuch

seriouspotentialdangersastheseshouldbeusedonlyiflifeisthreatenedandnothingelsewillwork.Allthepossible

troublesthatcanresultfromantibiotictreatmentshouldnotkeepanyonefromusingoneofthesedrugswhenitisclearly

indicated.Norshouldtheydiscouragecertainpreventiveusesofantibioticswhichhaveprovedextremelyvaluable.

抗生素的另一面抗生素已經(jīng)消除或控制了很多傳染病,實(shí)際上每個(gè)人都從這種或那種使用中受益.即使沒有這樣的個(gè)人經(jīng)驗(yàn),人們也不得不孤立地認(rèn)識(shí)到這些"奇跡"藥物的優(yōu)點(diǎn),真實(shí)性和推測(cè)性.美國(guó)新聞界,廣播電臺(tái)和電視臺(tái)在報(bào)道有關(guān)細(xì)菌化學(xué)戰(zhàn)爭(zhēng)成功的真實(shí)故事方面做得很好.更重要的是,制造和銷售抗生素的制藥公司的積極的公共關(guān)系活動(dòng)已經(jīng)彌補(bǔ)了他們的缺點(diǎn).相比之下,這些顯著的藥物的不足之處和潛在的危險(xiǎn)是廣為人知的.缺乏這樣的知識(shí)可能是不好的,