医学英语教程Chapter 5Digestive System

Chapter5DigestiveSystem

I.Introduction

Thedigestiveorgastrointestinalsystembeginswiththemouth,wherefoodenters,andendswith

theanus,wheresolidwastematerialleavesthebody.Thethreefunctionsofthesystemare

digestion,absorption,andelimination.

First,complexfoodmaterialtakenintothemouthisdigested,orbrokendown,mechanicallyand

chemically,asittravelsthroughthegastrointestinaltract.Digestiveenzymesspeedupchemical

reactionsandaidthebreakdownofcomplexnutrients.Complexproteinsaredigestedtosimpler

aminoacids;complicatedsugarsarereducedtosimplesugars,suchasglucose;andlargefat

moleculesarebrokendowntofattyacidsandglycerol.

Second,viaabsorptiondigestedfoodpassesintothebloodstreamthroughthewallsofthesmall

intestine.Thus,valuablenutrientstraveltoallcellsofthebody.Cellsthencatabolizenutrientsin

thepresenceofoxygentoreleaseenergystoredwithinthefood.Cellsalsouseaminoacid

nutrientstoanabolizelargeproteinmoleculesneededforgrowthanddevelopment.Althoughthe

wallsofthesmallintestinealsoabsorbfattyacidsandglycerol,thesenutrientsenterlymphatic

vesselsratherthanbloodvessels.Digestedfatseventuallyenterthebloodstreamaslymphvessels

joinwithbloodvesselsintheupperchestregion.

II.AnatomyandPhysiology

OralCavity

Thegastrointestinaltractbeginswiththeoralcavity.Oralmeanspertainingthemouth.Label

Figure5-1asyoulearnthemajorpartsoftheoralcavity.

Thecheeksformthewallsoftheoval-shapedoralcavity,andthelipssurroundtheopeningtothe

cavity.

Thehardpalateformstheanteriorportionoftheroofthemouth,andthemuscularsoftpalatelies

posteriortoit.Rugaeareirregularridgesinthemucousmembranecoveringtheanteriorportionof

thehardpalate.Theuvula,asmallsofttissueprojection,hangsfromthesoftpalate.Itaids

productionofsoundsandspeech.

Thetongueextendsacrosstheflooroftheoralcavity,andmusclesattachittothelowerjawbone.

Itmovesfoodaroundduringmastricationanddeglutition,papillae,smallraisedareasonthe

tongue,containtastebudsthataresensitivetothechemicalnatureoffoodsandallow

discriminationofdifferenttastesasfoodmovesacrossthetongue.

Thetonsils,massesoflymphatictissuelocatedindepressionsofthemucousmembranes,lieon

bothsidesoftheoropharynx.Theyarefilterstoprotectthebodyfromtheinvasionof

microorganismsandtheyproducelymphocytes,disease-fightingwhitebloodcells.

Thegumsarefleshytissuethatsuiroundthesocketsoftheteeth.Figure5-2showsadentalarch

with16permanentteeth,lablethefigurewiththefollowingnamesofteeth:

Central[I]Lateralincisor[2]Canine[3]Firstpremolar[4]

Secondpremo;ar[5]Firstmolar[6]Secondmolar[7]Thirdmolar[8]

Figure5-1

Oralcavity

Dentistsusespecitaltermstodescribethesurfacesofteeth.Thelabialsurface,forincisorand

canineteeth,isnearestthelips.Thebuccalsurface,forpremolarandmolarteeth,liesadjacentto

cheek,asillstratedinFigure5-2.Dentistsrefertoboththelabialandthebuccalsurfacesasthe

facialsurface,oppositetothefacialsurface,allteethhavealingualsurface.Themesialsurfaceof

atoothliesnearesttothemedianlineandthedistalsurface,farthestfromthemedialline.

Premolarsandmolarshaveanadditionalocclusalsurfacethatcomesincontactwitha

correspondingtoothintheoppsingarch.Theincisorsandcanineshaveasharpincisaledge.

Figure5-2

Upperpermanentteethwithinthedentalarch.

Figure5-3showstheinneranatomyofatooth,labelitasyoureadthefollowingdescription:

Atoothconsistsofacrown,whichshowsabovethegumline,andaroot,whichlieswithinthe

bonytoothsocket.Theoutermostprotectivelayerofthecrown,theenamel,protectsthetooth.

Enamelisadense,hard,whitesubstance-thehardestsubstanceinthebody.Dentin,themain

substanceofthetooth,liesbeneaththeenamelandextendsthroughoutthecrown.Yellowincolor,

dentiniscomposedofbonytissuethatissofterthanenamel.Thecementumcovers,protects,and

supportsthedentinintheroot.Aperiodontalmembranesurroundsthecementumandholdsthe

toothinplaceinthetoothsocket.

Thepulpliesunderneaththedentin.Thissoftanddelicatetissuefillsthecenterofthetooth.Blood

vessels,nerveendings,connectivetissue,andlymphaticvesselsarewithinthepulpcanal.Root

canaltherapyisoftennecessarywhendiseaseorabscessoccursinthepulpcanal.Adentistopens

thetoothfromaboveandcleansthecanalofinfection,nerves,andbloodvessels.Thecanalisthen

disinfectedandfilledwithmaterialtopreventtheentranceofmicroorganismsanddecay.

Threepairsofsalivaryglandssurroundtheoralcavity.Theseexocrineglandsproducesalivathat

containsimportantdigestiveenzymes.Saalivaisreleasedfromtheparotidgland,submandibular

gland,andsublingualglandoneachsideofthemouth.Narrowductscarrysalivaintotheoral

cavity.

Figure5-3

Anatomyofatooth

Figure5-4

Salivaryglands

Pharynx

Refertofinuge5-5.Thepharynxorthroatisamusculartube,about5incheslonglinedwitha

mucousmembrane.Itisacommonpassagewayforairtravelingfromthenosetothewindpipeand

foodtravelingfromtheoralcavitytotheesophagus.Whenswallowingoccurs,aflapfotissue,the

epiglottis,coversthetracheasothatfoodcannotenterandbecomelodgedthere.Seefigure5-5A

andB.

Figure5-5

Deglutition.(A)Epiglottisclosesoverthetracheaasthebolusoffoodpassesdownthepharynx

towardtheesophagus.(B)Epiglottisopensasthebolusmovesdowntheesophagus

Figure5-6tracesthepassageoffoodfromtheesophagusthroughthegastrointestinaltract.Label

itasyoureadthefollowingparagraphs.

Thegastrointestinaltract

Esophagus

Theesophagusisa9-to10-inchmuscilartubeextendingfromthepharynxtothestomach.

Peristalsisistheinvoluntary,progressive,rhythmiccontractionofmusclesinthewallofthe

esophaguspropellingabolustowardthestomach.Theprocessislikesqueezingamarblethrough

arubbertube.

Stomach

Foodpassesfromtheesophagusintothestomach.Thestomachhasthefollowingthreeparts:

fundus,body,andantrum.Ringsofmusclescalledsphincterscontroltheopeningsintoand

leadingoutofthestomach.Theloweresophagealsphincterrelaxesandcontractstomovefood

fromtheesophagusintothestomach,whereasthepyloricsphincterallowsfoodtoleavethe

stomachwhenitisready.Foldsinthemucousmembraneliningthestomacharecalledrugae.The

rugaecontaindigestiveglandsthatproducetheenzymepepsinandhydrochloricacid.

Thestomachpreparesfoodforthesmallintestine,wheredigestionandabsorptionintothe

bloodstreamtakeplace.Thestomachcontrolspassageoffoodsintothefirstpartofthesmall

intestinesothatitproceedsonlywhenitischemicallyreadyandinsmallamounts.Foodleaves

thestomachin1to4hoursorlonger,dependingontheamountandtypeoffoodeaten.

Greater

curvature

Figure5-7

Partsofthestomach.Thefundusandbodyareareservoirforingestedfoodandanareaforaction

byacidandpepsin.Theantrumisamusculargrindingchamberthatpulverizesfoodandfeedsit

graduallyintotheduodenum

SmallIntestine

Thesmallintestineextendsfor20feetfromthepyloricsphinctertothefirstpartofthelarge

intestine.Ithasthreeparts.Thefirstsection,theduodenum,isonly1footlong.Itreceivesfood

fromthestomachaswellasbilefromtheliverandgallbladderandpancreaticjuicefromthe

pancereas.Enzymesandbilehelpdigestfoodbeforitpassesintothesecondpartofthesmall

intestine,thejejunum,about8feetlong.Thejejunumconnectswiththethirdsection,theileum,

about11feetlong.Theileumattachestothefirstpartofthelargeintestine.

Millionsoftiny,microscopicprojectionscalledvillilinethewallsofthesmallintestine.Thetiny

capillariesinthevilliabsorbthedigestednutrientsintothebloodstreamandlymphvessels.Figure

5-8showsseveraldifferentviewsofvilliintheliningofthesmallintestine.

LargeIntestine

Thelargeintestineextendsfromtheendoftheileumtotheanus.Ithassixsections:cecum,

ascendingcolon,transeversecolon,descendingcolon,sigmoidcolon,andrectum.Thececumisa

pouchontherightsidethatconnectstotheileumattheileocecalvalve.Theappendixhangsfrom

thececum.Theappendixhashasnoclearfunctionandcanbecomeinflamedandinfectedwhen

cloggedorblocked.Thecolon,about5feetlong,hasthreedivisions.Theascendingcolonextends

fromthececumtotheundersurfaceoftheliver,whereitturnstothelefttobecomethetransverse

colon.Thetransversecolonpasseshorizontallytothelefttowardthespleen,andturnsdownward

intothedescendingcolon.Thesigmoidcolon,shapedlikeanSresemblingtheGreeklettersigma,

whichcurves,liesatdistalendofthedescendingcolonandleadsintotherectum.Therectum

terminatesintheloweropeningofthegastrointestinaltract,theanus.

Thelargeintestinerecivesthefluidwasteproductsofdigestionandstoresthesewastesuntilthey

canbereleasedfromthebody.Becausethelargeintestineabsorbsmostofthewaterwithinthe

wastematerial,thebodycanexpelsolidfeces.Defectionistheexpulsionorpassageoffecesfrom

thebodythroughtheanus.Diarrhea,orwaterystools,resultsfromreducedwaterabsorptioninto

thebloodstreamthroughthewallsofthelargeintestine.

Liver,Gallbladder,andPancreas

Threeimportantadditionalorgansofthedigestivesystem-theliver,gallbladder,andpancreas-play

crucialrolesintheproperdigestionandabsorptionofnutrients.labelFigure5-9asyoustudythe

following:

Theliver,locatedintherightupperquadrantoftheabdomen,manufacturesathick,orange-black,

sometimesgreenish,fluidcalledbile.Bilecontainscholesterol,bileacids,andseveralbile

pigments.Oneofthesepigments,bilirubin,isproducedfromthebreakdownofhemoglobinduring

normalredbloodcelldestruction.Bilirubintravelsviathebloodstreamtotheliver,whereitis

conjugatedwithanothersubstanceandaddedtobile.Thus,conjugatedbilirubinentersthe

intestinewithbile.Bacteriainthecolondegradebilirubinintoavarietyofpigmentsthatgive

fecesabrownishcolor.Bilirubinandbileleavethebodyinfeces.

Figure5-8

Villiintheliningofthesmallintestine

Figure5-9

Liver,gallbladder,andpancreas

Redbloodcell

destructionand

hemoglobinbreakdown

produce...

BILIRUBIN-Inblood

BILIRUBINandBILE

(degraded)

Colon

BILtRUBINandBILE

Loavethobodyinfeces

Figure5-10

Billirubinpathwayfrombloodstreamtoeliminationinfeces.

BloodstreamDuodenum

tocellsfordigestion

Figure5-11

Thepancreasanditsfunctions

Ifbilirubincannotleavethebody,itremainsinthebloodstream,causingjaundice,yellow

discolorationfotheskin,whitesoftheeyes,andmucousmembranes.Figure5-10reviewsthepath

ofbilirubinfromredbloodbloodcelldestructiontoeliminationwithbileinthefeces.

Thelivercontinuouslyreleasesbile,whichthentravelsthroughthehepaticducttothecysticduct.

Thecysticductleadstothegallbladder,apear-shapedsacundertheliver,whichstoresand

concentratesthebileforlateruse.Aftermeals,inresponsetothepresenceoffoodinthestomach

andduodenum,thegallbladdercontracts,forcingtheboleoutthecysticductintothecommonbile

duct.Meanwhile,thepancreassecretespancreaticjuicesthattravelviathepancreaticducttojoin

withthecommonbileductasitenterstheduodenum.Theduodenumthusreveivesamixtureof

bileandpancreaticjuices.

Bilehasadetergent-likeeffectoffatsintheduodenum.Intheprocessofemulsification,bile

breaksapartlargefatglobules,creatingmoresurfaceareasothatenzymesfromthepancreascan

digestthefats.Withoutbile,mostofthefattakenintothebodyremainsundigested.

Besidesproducingbile,theliverhasseveralothervitalandimportantfunctions:

1.Maintainingnormalbloodglucoselevels.Theliverremovesexcessglucosefromthe

bloodstreamandstoresitasglycogeninlivercells.Whenthebloodsugarlevelbecomes

dangerouslylow,theliverconvertsstoredglycogenbackintoglucoseviaaprocesscalled

glycogenolysis.Inaddition,thelivercanalsoconvertproteinsandfatsintoglucose,whenthe

bodyneedssugar,byaprocesscalledgluconeogenesis.

2.manufacturingbloodproteins,particularlythosenecessaryforbloodclotting

3.Releasingbilirubin,apigmentinbile

4.Removingpoisonsfromtheblood

Theprotalveinbringsbloodtheliverfromtheintestines.Digestedfoodspassintotheportalvein

directlyafterbeingabsorbedintothebloodstreamfromthesmallintestine,thusgivingtheliver

thefirstchancertousethenutrients.

Thepancreasisbothanexocrineandanendocrineorgan.Asanexocrinegland,itproduces

enzymestodigeststarch,suchasamylase,todigestfat,suchaslipase,andtodigestproteins,

suchasprotease.Thesepassintotheduodenumthroughthepancreaticduct.

Asanendocrinegland,thepancreassecretesinsulin.Thishromone,neededtohelpreleasesugar

fromtheblood,actsasacarriertobringglucoseintocellsofthebodytobeusedforenergy.

Figure5-12isaflowchartthattracesthepathwayoffoodthroughthegastrointestinaltract

ANUS

Fecesleavethebody

Figure5-12

Pathwayoffoodthroughthegastrointestinaltract

III.Vocabulary

Thislistreviewsmanynewtermsintroducedinthetext.Shortdefinitionsandadditional

informationreinforceyourunderstandingoftheterms.SeeSectionVIIIofthischapterfor

pronuciationofterms.

absorptionPassageofmaterialsthroughthewallsoftheintestineintothebloodstream

aminoacidsBuildingblocksofproteinsandproducedwhenproteinsaredigested

amylaseEnzymesecretedbythepancreastodigeststarch.

anusOpeningofthedigestivetracttotheoutsideofthebody

appendixBlindpouchhangingfromthececum.Itliterallymeans“hanging"“on”

bileDigestivejuicemadeintheliverandstoredinthegallbladder.Itbreaksuplarge

fatglobules.Bilewasoriginallycalledgall,proballybecauseithasabitter

taste.Itiscomposedofbilepigments,cholesterol,andbilesalts.

bilirubinPigmentreleasedbytheliverinbile

bowelintestine

canineteethPointed,dog-liketeeth,nexttotheincisors.Alsocalledcuspidsoreyeteeth

cecumFirstpartofthelargeintestine

colonlargeintestine

commonbileductCamesbilefromtheliverandgallbladdertotheduodenum

defecationExpulsionorpassageoffecesfromthebodythroughtheanus

deglutitionSwallowing

dentinMajortissuecomposingteeth,coveredbytheenamelinthe

crownandaprotectivelayerofcementumintheroot

digestionBreakdownofcomplexfoodstosimplerforms

duodenumFirstpartofthesmallintestine,Duo=2,den=10;theduodenummeasures

12incheslong.

eliminationRemovalofwastematerialfromthebody

emulsificationPhysicalprocessofbreakinguplargefatgloulesintosmallerglobules,

thusincreasingthesurfaceareathatenzymescanusetodigestthefat

enamelHard,outermostlayerofatooth

enzymeAchemicalthatspeedsupareactionbetweensubstances.Digestiveenzymeshelpinthe

breakdownofcomplexfoodstosimplerfoods

esophaugsTubeconnectingthethroattothestomach.Eso-meansinward;phag/omeans

swallowing

fattyacidSubstancesproducedwhenfataredigested

fecesSolidwastes;stools

gallbladderSmallsacundertheliver;storesbile

glucoseSmiplesugar

glycogenStarch;glucoseisstoredintheformofglycogeninlivercells

hydrochloricacidSubstanceproducedbythestomach,necessaryfordigestionoffood

ileumThirdpartofthesmallintestine;fromtheGreekeilos,meaning“twisted."Whenthe

abdomenwasviewedatautopsy,theintestineappearedtwistedandtheileumwasoften

anareaofobstruction

incisorOneoffourfrontteethinthedentalarch

insulinHormoneproducedbytheendocrinecellsofthepancreas.Ittransportssugarfromthe

bloodintocellsandstimulatesglycogenformationbytheliver

jejunumSecondpartofthesmallintestine.Thelatinjejunusmeans“empty"；thispartofthe

intestinewasalwaysemptywhenabodywasexaminedafterdeath.

lioasePancreaticenzymenecessarytodigestfats

liverAlargeorganlocatedintheRUQoftheabdomen.Theliversecreatesbiles;storessugar,

iron,andvitamins;producesbloodproteins;anddestroyswornoutreadbloodcells.

loweresophagealRingofmusclesbetweentheesophagusandthestomach.Alsocalledcariacsphincter

sphincter

masticationChewing

molarteethSixth,seventh,andeighthteethfromthemiddleoneithersideofthedental

arch.Premolarteetharethe4than(j5“teeth,beforethemolars

palateRoofofthemouth.Thehardpalateliesanteriortothesoftpalate

pancreasorganunderthestomach;producesinsulinandenzymes

papillaeSmallelevationsonthetongue.Apapillaisanipple-likeelevation

parotidglandSalivaryglandonthetongue.Apapillaisanipple-likeelevation

peristalsisPhythm-likecontractionsofthetubesofthegastrointestinaltractandother

tubularstructures.ReristalsismovesthecontentsthroughtheGItractat

differentrates;stomach,smallintestine,andcolonperi-meanssurround

and-stalsisisconstriction

pharynxThroat,thecommonpassagewayforfoodfromthemouthandairfromthenose

portalveinLargeveinbringingbloodtotheliverfromtheintestines

proteaseenzymesthatdigestprotein

pulpSofttissuewithinatooth,containingnervesandbloodvessels

pyloricsphincterRingofmusclefibersatthedistalregionofthestomach,whereitjoinsthe

duodenum.FromGreekpyloros,meaning“gatekeeper.”

rectumlastsectionofthecolon

rugaeRidgesonthehardpalateandthewallofthestomach

salivaDigestivejuiceproducedbysalivaryglands

salivaryglandsParotid,sublingual,andsubmandibularglands

sigmoidcolonLowerpartofthecolon;shapedlikeanS

sphincterRingofmusclefibersthatconstrictsapassageorclosesanaturalopening

stomachMuscularorganthatreceivesfoodfromtheesophagus.Thestomach'sparts

arethefundus,body,andantrum.

triglyceridesLargefatmoleculescomposedofthreepartsfattyacidandonepartglycerol

uvulaSofttissuehangingfromthesoftpalateintothemouth.Latin,uvameans

“grape.”

villyMicroscopicprojectionsinthewallsofthesmallintestinethatabsorb

nutrientsintothebloodstream.

IV.CombiningForms,Suffixes,andTerminology

CheckSectionVIIIofthischapterforhelpwithpronunciationofterms.Writethemeaningofthe

medicalterminthespaceprovided

Partsofthebody

CombiningFormMeaningTerminologyMeaning

an/oanusPerianal_________

append/oappendixappendectomy____—

appendic/oappendixappendicitis

SeeFigure5-13

bucc/ocheekbuccalmucosa

Amucosaiscomposedofepithelialcells

cec/ocecumcecal.

celi/obelly,abdomenceliac_______________________________

Abdomin/oandlaper/oalsomeanabdomen.

Whenmorethanonecombiningformhasthe

samemeaning,noruleexistsfortheproper

usageofoneortheother.Youwilllearnto

recognizeeachinitspropercontext.

Figure5-13

Stagesofappendicitis.(A)Obstructionandbacterialinfectioncausered,swollen,andinflamed

appendix.(B)Pusandbacteriainvadethewalloftheappendix.(C)Pusperforatesthewallofthe

appendixintotheabdomen,leadingtoperitonitis.

cheil/olipcheilosis_________________________________

labi/oalsomeanslip

cheolecyst/ogallbladdercholecystectomy___________________________

choledoch/ocommonbileductcholedochotomy___________________________

col/ocolon,largeintestinechostomy________________________________

-stomy,whenusedwithacombiningformforan

organ,emansanopeningtotheuotsideofthe

body.Astomaisanopeningbetweenanorgan

andthesurfaceofthebody

colon/ocoloncolonic_________________________________

colonoscopy_____________________________

dent/Itoothdentibuccal________________________________

Odont/oalsomeanstooth

enter/ointestines,usuallysmallintestineenterocolitis______________________________

Whentwocombiningformsforgastrointestinal

organsareinaterm,theoneclosesttothe

mouthappearsfirst

Figure5-14

(A)Sigmoidcolostomyafterresectionoftherectumandpartofthesigmoidcolon.(B)Ileostomy

afterresectionoftheentirecolon.Theileumisdrawnthroughtheabdominalwalltoforman

ileostomystoma

enterocolostomy_________________________

-stomy,whenusedwithtwoormore

combiningformsfororgans,meansthesurgical

creationofanopeningbetweenthoseorgans

insidethebody.Thisisananastomosis,whichis

anysurgicalconnectionbetweentwoparts,such

asvessels,ductsorbowelsegments

mesentery_______________________________

Partofthedoublefoldofperitoneumthat

stretchesaroundtheorgansintheabdomen,the

mesenteryholdstheorgansinplace.Literally,it

liesinthemiddleoftheintestines,amembrane

attachingtheintestinestothemusclewallatthe

backoftheabdomen

parenteral_______________________________

parmeansapartfrominthisterm.An

intravenouslinebringspaenteralnutrition

directlyintothebloodstream,bypassingthe

intestinaltract.Parenteralinjectionscanbe

subcutaneousandintramuscular,aswell

esophag/oesophagusesophageal

Note:Changingthesuffixfrom-alto-eal

softensthefinal"g"

ANASTOMOSES

Omentum

Endend

Transverse

colon

Mesocolon

Descending

colon

Mesentery

Sigmoid

colon

Bladder

Figure5-15

(A)Threetypesofanastomoses.(B)Mesentery.Theomentumandmesocolonarepartsofthe

mesentery.Theomentumactuallyhangsdownlikeanapronovertheintestines

faci/ofacefacial_______________________________

gastr/ostomachgastrostomy__________________________

gingiv/ogumsgingivitis___________________________