1、药学英语第五版原文翻译IntroductiontoPhysiologyIntroductionPhysiologyisthestudyofthefunctionsoflivingmatter.Itisconcernedwithhowanorganismperformsitsvariedactivities:howitfeeds,howitmoves,howitadaptstochangingcircumstances,howitspawnsnewgenerations.Thesubjectisvastandembracesthewholeoflife.Thesuccessofphysiolog
2、yinexplaininghoworganismsperformtheirdailytasksisbasedonthenotionthattheyareintricateandexquisitemachineswhoseoperationisgovernedbythelawsofphysicsandchemistry.Althoughsomeprocessesaresimilaracrossthewholespectrumofbiologythereplicationofthegeneticcodefororexamplemanyarespecifictoparticulargroupsofo
3、rganisms.Forthisreasonitisnecessarytodividethesubjectintovariouspartssuchasbacterialphysiology,plantphysiology,andanimalphysiology.Tostudyhowananimalworksitisfirstnecessarytoknowhowitisbuilt.Afullappreciationofthephysiologyofanorganismmustthereforebebasedonasoundknowledgeofitsanatomy.Experimentscant
4、henbecarriedouttoestablishhowparticularpartsperformtheirfunctions.Althoughtherehavebeenmanyimportantphysiologicalinvestigationsonhumanvolunteers,theneedforprecisecontrolovertheexperimentalconditionshasmeantthatmuchofourpresentphysiologicalknowledgehasbeenderivedfromstudiesonotheranimalssuchasfrogs,r
5、abbits,cats,anddogs.Whenitisclearthataspecificphysiologicalprocesshasacommonbasisinawidevarietyofanimalspecies,itisreasonabletoassumethatthesameprincipleswillapplytohumans.Theknowledgegainedfromthisapproachhasgivenusagreatinsightintohumanphysiologyandendoweduswithasolidfoundationfortheeffectivetreat
6、mentofmanydiseases.Thebuildingblocksofthebodyarethecells,whicharegroupedtogethertoformtissues.Theprincipaltypesoftissueareepithelial,connective,nervous,andmuscular,eachwithitsowncharacteristics.Manyconnectivetissueshaverelativelyfewcellsbuthaveanextensiveextracellularmatrix.Incontrast,smoothmuscleco
7、nsistsofdenselypackedlayersofmusclecellslinkedtogetherviaspecificcelljunctions.Organssuchasthebrain,theheart,thelungs,theintestines,andtheliverareformedbytheaggregationofdifferentkindsoftissues.Theorgansarethemselvespartsofdistinctphysiologicalsystems.Theheartandbloodvesselsformthecardiovascularsyst
8、em;thelungs,trachea,andbronchitogetherwiththechestwallanddiaphragmformtherespiratorysystem;theskeletonandskeletalmusclesformthemusculoskeletalsystem;thebrain,spinalcord,autonomicnervesandganglia,andperipheralsomaticnervesformthenervoussystem,andsoon.Cellsdifferwidelyinformandfunctionbuttheyallhavece
9、rtaincommoncharacteristics.Firstly,theyareboundedbyalimitingmembrane,theplasmamembrane.Secondly,theyhavetheabilitytobreakdownlargemoleculestosmalleronestoliberateenergyfortheiractivities.Thirdly,atsomepointintheirlifehistory,theypossessanucleuswhichcontainsgeneticinformationintheformofdeoxyribonucle
10、icacid(DNA).Livingcellscontinuallytransformmaterials.Theybreakdownglucoseandfatstoprovideenergyforotheractivitiessuchasmotilityandthesynthesisofproteinsforgrowthandrepair.Thesechemicalchangesarecollectivelycalledmetabolism.Thebreakdownoflargemoleculestosmalleronesiscalledcatabolismandthesynthesisofl
11、argemoleculesfromsmalleronesanabolism.Inthecourseofevolution,cellsbegantodifferentiatetoservedifferentfunctions.Somedevelopedtheabilitytocontract(musclecells),otherstoconductelectricalsignals(nervecells).Afurthergroupdevelopedtheabilitytosecretedifferentsubstancessuchashormonesorenzymes.Duringembryo
12、logicaldevelopment,thisprocessofdifferentiationisre-enactedasmanydifferenttypesofcellareformedfromthefertilizedegg.Mosttissuescontainamixtureofcelltypes.Forexample,bloodconsistsofredcells,whitecells,andplatelets.Redcellstransportoxygenaroundthebody.Thewhitecellsplayanimportantroleindefenseagainstinf
13、ectionandtheplateletsarevitalcomponentsintheprocessofbloodclotting.Thereareanumberofdifferenttypesofconnectivetissuebutallarecharacterizedbyhavingcellsdistributedwithinanextensivenoncellularmatrix.Nervetissuecontainsnervecellsandglialcells.ThePrincipalOrganSystemsThecardiovascularsystemThecellsoflar
14、gemulticellularanimalscannotderivetheoxygenandnutrientstheyneeddirectlyfromtheexternalenvironment.Theoxygenandnutrientsmustbetransportedtothecells.Thisisoneoftheprincipalfunctionsoftheblood,whichcirculateswithinbloodvesselsbyvirtueofthepumpingactionoftheheart.Theheart,bloodvessels,andassociatedtissu
15、esformthecardiovascularsystem.Theheartconsistsoffourchambers,twoatriaandtwoventricles,whichformapairofpumpsarrangedsidebyside.Therightventriclepumpsdeoxygenatedbloodtothelungswhereitabsorbsoxygenfromtheair,whiletheleftventriclepumpsoxygenatedbloodreturningfromthelungstotherestofbodytosupplythetissue
16、s.Physiologistsareconcernedwithestablishingthefactorsresponsiblefortheheartbeat,howtheheartpumpsthebloodaroundthecirculation,andhowitisdistributedtoperfusethetissuesaccordingtotheirneeds.Fluidexchangedbetweenthebloodplasmaandthetissuespassesintothelymphaticsystem,whicheventuallydrainsbackintothebloo
17、d.TherespiratorysystemTheenergyrequiredforperformingthevariousactivitiesofthebodyisultimatelyderivedfromrespiration.Thisprocessinvolvestheoxidationoffoodstuffstoreleasetheenergytheycontain.Theoxygenneededforthisprocessisabsorbedfromtheairinthelungsandcarriedtothetissuesbytheblood.Thecarbondioxidepro
18、ducedbytherespiratoryactivityofthetissuesiscarriedtothelungsbythebloodinthepulmonaryarterywhereitisexcretedintheexpiredair.Thebasicquestionstobeansweredincludethefollowing:HowistheairmovedinandoutofthelungsHowisthevolumeofairbreathedadjustedtomeettherequirementsofthebodyWhatlimitstherateofoxygenupta
19、keinthelungsThedigestivesystemThenutrientsneededbythebodyarederivedfromthediet.Foodistakeninbythemouthandbrokendownintoitscomponentpartsbyenzymesinthegastrointestinaltract.Thedigestiveproductsarethenabsorbedintothebloodacrossthewalloftheintestineandpasstotheliverviatheportalvein.Thelivermakesnutrien
20、tsavailabletothetissuesbothfortheirgrowthandrepairandfortheproductionofenergy.Inthecaseofthedigestivesystem,keyphysiologicalquestionsare:HowisfoodingestedHowisitbrokendownanddigestedHowaretheindividualnutrientsabsorbedHowisthefoodmovedthroughthegutHowaretheindigestibleremainseliminatedfromthebodyThe
21、kidneysandurinarytractThechieffunctionofthekidneysistocontrolthecompositionoftheextracellularfluid.Inthecourseofthisprocess,theyalsoeliminatenon-volatilewasteproductsfromtheblood.Toperformthesefunctions,thekidneysproduceurineofvariablecompositionwhichistemporarilystoredinthebladderbeforevoiding.Thek
22、eyphysiologicalquestionsinthiscaseare:howdothekidneysregulatethecompositionofthebloodHowdotheyeliminatetoxicwasteHowdotheyrespondtostressessuchasdehydrationWhatmechanismsallowthestorageandeliminationoftheurineThereproductivesystemReproductionisoneofthefundamentalcharacteristicsoflivingorganisms.Theg
23、onadsproducespecializedsexcellsknownasgametes.Atthecoreofsexualreproductionisthecreationandfusionofthemaleandfemalegametes,thespermandova(eggs),withtheresultthatthegeneticcharacteristicsoftwoseparateindividualsaremixedtoproduceoffspringthatdiffergeneticallyfromtheirparents.ThemusculoskeletalsystemTh
24、isconsistsofthebonesoftheskeleton,skeletalmuscles,joints,andtheirassociatedtissues.Itsprimaryfunctionistoprovideameansofmovement,whichisrequiredforlocomotion,forthemaintenanceofposture,andforbreathing.Italsoprovidesphysicalsupportfortheinternalorgans.Herethemechanismofmusclecontractionisacentralissu
25、e.Theendocrineandnervoussystems.TheendocrineandnervoussystemsTheactivitiesofthedifferentorgansystemsneedtobecoordinatedandregulatedsothattheyacttogethertomeettheneedsofthebody.Twocoordinatingsystemshaveevolved:thenervoussystemandtheendocrinesystem.Thenervoussystemuseselectricalsignalstotransmitinfor
26、mationveryrapidlytospecificcells.Thusthenervespasselectricalsignalstotheskeletalmusclestocontroltheircontraction.Theendocrinesystemsecreteschemicalagents,hormones,whichtravelinthebloodstreamtothecellsuponwhichtheyexertaregulatoryeffect.Hormonesplayamajorroleintheregulationofmanydifferentorgansandare
27、particularlyimportantintheregulationofthemenstrualcycleandotheraspectsofreproduction.Theimmunesystemprovidesthebodysdefensesagainstinfectionbothbykillinginvadingorganismsandbyeliminatingdiseasedordamagedcells.Althoughitishelpfultostudyhoweachorganperformsitsfunctions,itisessentialtorecognizethatthea
28、ctivityofthebodyasawholeisdependentontheintricateinteractionsbetweenthevariousorgansystems.Ifonepartfails,theconsequencesarefoundinotherorgansystemsthroughoutthewholebody.Forexample,ifthekidneysbegintofail,theregulationoftheinternalenvironmentisimpairedwhichinturnleadstodisordersoffunctionelsewhere.
29、HomeostasisComplexmechanismsareatworktoregulatethecompositionoftheextracellularfluidandindividualcellshavetheirownmechanismsforregulatingtheirinternalcomposition.Theregulatorymechanismsstabilizetheinternalenvironmentdespitevariationsinboththeexternalworldandtheactivityoftheanimal.Theprocessofstabili
30、zationoftheinternalenvironmentiscalledhomeostasisandisessentialifthecellsofthebodyaretofunctionnormally.Takingoneexample,thebeatingoftheheartdependsontherhythmicalcontractionsofcardiacmusclecells.Thisactivitydependsonelectricalsignalswhich,inturn,dependontheconcentrationofsodiumandpotassiumionsinthe
31、extracellularandintracellularfluids.Ifthereisanexcessofpotassiumintheextracellularfluid,thecardiacmusclecellsbecometooexcitableandmaycontractatinappropriatetimesratherthaninacoordinatedmanner.Consequently,theconcentrationofpotassiumintheextracellularfluidmustbekeptwithinanarrowrangeiftheheartistobea
32、tnormally.HowDoesTheBodyRegulateItsOwnCompositionTheconceptofbalanceInthecourseofaday,anadultconsumesapproximately1kgoffoodanddrinks23litersoffluid.Inamonth,thisisequivalenttoaround30kgoffoodand6090litersoffluid.Yet,ingeneral,bodyweightremainsremarkablyconstant.Suchindividualsaresaidtobeinbalance;th
33、eintakeoffoodanddrinkmatchestheamountsusedtogenerateenergyfornormalbodilyactivitiesplusthelossesinurineandfeces.Insomecircumstances,suchasstarvation,intakedoesnotmatchtheneedsofthebodyandmuscletissueisbrokendowntoprovideglucoseforthegenerationofenergy.Here,theintakeofproteinislessthantherateofbreakdownandtheindividualissaidto
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