消化系統(tǒng)英文

Ch23-DigestiveSystem,Part2SmallintestinePancreasLiver

-HepaticportalsystemGallbladder

-BileLargeIntestineChemicaldigestionandabsorptionJunctionofstomachandsmallintestineSmallIntestineMajorfunction-responsiblefor90%ofabsorptionandalsoimportantfordigestionDividedintothreeregionsDuodenum-‘mixingbowl’Jejunum-chemical

digestion/absorptionIleum-protection

fromlargeintestineLayersofthesmallintestinePlicaUniquetothesmallintestineisthepresenceofplica(plicaecirculares).Plicaarepermanentfoldsofthemucosaandsubmucosa.Ontheplica,youwillseevilli-

-Presentonlyinsmallintestine-Cryptsspacedbetweenthem-Donotconfusewith‘mircovilli’OneplicaOnevillusPlicaandvilliEachplicasupportsaforestofvilli.Eachvillusiscoveredwithsimplecolumnarepithelium.Theseepithelialcellshavemicrovilli.Phew!VillusandenzymesofthebrushbordercellsmicrovilliBrushbordercellThelaminapropriaofeachvilluscontainsalacteal,nervesandbloodvesselsRegionalFeaturesoftheSmallIntestineDuodenum-siteofchymeentry,whereitisblastedwithHCO3-(andotherthings)Alongduodenum,pHofchymechangesfrom1-2to7-8MucusglandsofmucosaAlso,Brunner’sglands(submucosalglands)Jejunum-firsthalfhasnumerousplicaeandvilli,buttheydecreaseinnumberenroutetoileumBrushborderenzymesIleum-lackplicae,

containmassesof

lymphoidtissue..why??DuodenumPlicaVilliCryptsBrunner’sGlands(submucosalglands)Jejunum-PanoramaIleumCryptsGobletCellsPeyer’sPatchesWhatorganssecreteintothesmallintestine?GallbladderLiverAnatomyofthepancreas-AnaccessorystructureofthesmallintestinePancreasWherehaveyouseenthepancreasbefore?Primarilyanexocrinegland(99%ofcells)Composedofaseriesofductulesthataresurroundedbysecretorycells,acinarcells

CuboidalepithelialcellsthatformpancreaticaciniPancreaticjuiceproducedbyacinarcellsAlkalinemixtureofenzymes,water,andionsOver1200mlof‘juice’producedeachday!Travelsinpancreaticduct,joinsthecommonbileductAcinarCellsEnzymesproducedbythepancreasPancreaticalpha-amylasePancreaticlipaseNucleasesFourinactiveproteolyticenzymesNotactivateduntiltheyreachthesmallintestineProteolyticEnzymesInactivetrypsinogenconvertedtoactivetrypsinbyenteropeptidase(enterokinase)TrypsinthenconvertsotherproenzymesintotheiractiveformsChymotrypsinCarboxypeptidase1234trypsinogenenteropeptidaseTrypsinisnowactive,and

willactivateotherproteases:

ChymotrypsinCarboxypeptidaseBrushbordercells56InactiveproteaseactiveproteaseInactiveproteasesreleased

fromacinarcellstrypsintrypsinTRYPSINLiverLargestvisceralorgan,3lbSurroundedbyfibrouscapsuleHasnumerouslobes,withnumerouslobulesCellsarecalledhepatocyesReceives~25%oftotalcardiacoutput!!BloodflowtoandfromtheliverisuniqueHepaticPortalSystemLiverreceives1/3ofbloodviahepaticartery(notshown)2/3fromhepaticportalveinThismajorveindrainscapillariesfrom:esophagus,stomach,smallandlargeintestineandTHENheadstoliverVenousbloodfromliverdumpsdirectlyintoinferiorvenacava

Anyguessesastoamajorfunctionoftheliver?HepaticPortalSystem-TheportalvenousbloodcontainsalloftheproductsofdigestionabsorbedfromtheGItract.

-Thusallnutrientsareprocessed/viewedintheliver(byhepatocytes)beforebeingreleasedbackintothecentralveins.LiverEachlobedividedintolobulesCellsoftheliverarehepatocytesArrangedasasinglelayerofcells,stackedDividedbysinusoidsBloodflowsthroughsinusoids,pastKupffercells(residentmacrophage)KupfferRBCsbacteriaLiverlobulesHepatocytesarrangedinto‘walls’.Wallsradiateoutwardfromacentralpoint.Thecentralareacontainsasingle,centralvein.BloodisflowingtowardscenterLiverlobules-PortalTriadsCentralVeinPortalTriad1mmMajorfunctionsoftheliverMetabolicregulationHematologicalregulationBileproduction

(itsonlytrue

digestivefunction)MetabolicRegulationHepatocytesregulatethecompositionofthebloodandbloodnutrientsTheydothisbyselectivelysecretingandabsorbingmoleculesfromthebloodWhatmolecules?Carbs,lipids,aminoacids,wasteproducts,vitamins,mineralsanddrugsPortaltriadMetabolicregulationHepatocytesadjustthecontentsofthebloodbyselectiveabsorptionandsecretionRemove/storeexcessnutrientsCorrectdeficienciesHepatocytesareabletotakeinand/orreleaselargemoleculeswithease,partlybecausethenearbycapillariesaresoleaky!hepatocytesAbigol’leakycapillary,asinusoidalcapillaryWhatroledoestheliverplayinaminoacidmetabolism?RemovesexcessaminoacidsfromthebloodstreamorreleasesstoredaminoacidsthataredeficientBesidesmaintenance/growth,whatmighttheseaminoacidsbeusedfor?Alanine,valine,leucine,proline,etc,etc.Whatroledoestheliverplayinlipidmetabolism?Regulatescirculatinglevelsoftriglycerides,fattyacids,andcholesterolIflevelsdecline,lipidstoresarebrokendownandreleasedALSO,wewillreturntoBilein3minutes,animportantplayerinlipidbreakdownWhatroledoestheliverplayincarbohydratemetabolism?Bloodglucoselevelsarekeptatornear90mg/dlIfbloodglucoselevelsrise,glucoseisstoredinliver

as______?

Ifglucoselevelsdrop,glycogenreservesintheliverarebrokendownandglucoseisreleasedintobloodOthermetabolicfunctionsoftheliverRemovalofwasteproductsAmmoniaisconvertedtoureaVitaminstorageThefatsolubleones!MineralstorageDruginactivationHematologicalregulationSynthesisofplasmaproteins(thinkalbumins,etc.)Removalofhormones(likeagiantsponge,thelivertakesNE,epi,thyroidhormones,steroidhormones,etc.‘outofthegame’)RemovalofantibodiesRemoval(orstorage)oftoxinsPhagocytosis(KupffercellschompupRBCsandareAPCs!)Productionofbile(1liter/day)KupfferRBCsHepatocytesproducebileBileismadeandthensecretedintochannelscalledbilecanaliculiCanaliculimergetojointhebileductsateachofthetriadstriadWhatisbile?Bileisanalkalinesolutioncontaining:water,electrolytes,bilirubin,phospholipids,triglycerides,cholesterol,andlipids

knownasbilesaltsFunctionofbile(bilesalts):

emulsifyfatsfordigestionBilesaltsarenotenzymes,theymerelyhelptobustuplargefatdropletsintosmallerfatdroplets.Whyisthisimportant?

GallBladderMajorfunctions:BilestorageBileconcentration,modificationGallbladderreceivesbilefromliverviathecysticductWhatregulatesreleaseofbile?Whenchymeentersthesmallintestine,CCKisreleasedCCKrelaxessphincter(sphincterofOddi)andtriggersmusclecontractionsthatsqueezethegallbladderandsendbileout,intoduodenumHowcleverthatCCKsecretionincreaseswhenchymeishighinfats!Interestingnote:CCKalsoslowsstomachmovement(releaseoffoodtoduodenum)Whatdoesthistellyouaboutahighfatmeal?ReviewofDigestionatSmallIntestineChymeentersduodenumfromstomachGetsblastedwithHCO3-,enzymesandbileWhichenzymes?Wherefrom?Areallenzymesactiveuponarrival?Whichonesare?Whichonesarenot?SegmentationprovidesmechanicaldigestionBilesaltssurroundfats,increasinglipaseeffectivenessABSORBPTIONofnutrients!!Oncemostabsorptiondone,twowavesofperistalsispushleft-oversintolargeintestines.Eachwavetakes~2hours.Animation-RecapThelastpart..largeintestineGeneralfunctionsReabsorptionofwaterAbsorptionofvitaminsmadebybacteriaCompactionandstorageoffecalmaterialAnatomyofthelargeintestineThelargeintestineis

comprisedofsections:CecumandappendixColon(ascending,transverse,descending,sigmoid)Rectum,leadsto

analcanalandanalcanalNote-

Largediameter

Thinwalls

HistologyoftheLargeIntestineColon-SimplecolumnarwithgobletcellsRectum-theanalcanalisstratifiedsquamousSo,asyoumovefromcolontoout:epitheliumchangesfromcolumnar(withgobletcells)

stratifiedsquamous

keratinizedstratifiedsquamous.MucosadoesnotproduceenzymesNovilliSiteof-

Vitamins,bile,andsomeH2OabsorptionAwordaboutbacterialfloraMostbacteriaareDOA(deadonarrival)atthelargeintestine,butsomesurviveandcomprisethebacterialfloraOver700species!Functions?ChemicalDigestionandAbsorptionVirtuallyallnutrientsfromthedietareabsorbedintoblood(orlymphvessels)acrossthemucosaofthesmallintestine.Muchofthisabsorptionhappensviaco-transportordiffusionacrosstheapicalmembraneofintestinalepithelialcells(thebrushbordercells),akaeneterocytesPart1&2FirststepsofmechanicalandchemicaldigestionPart3FinalstepsofchemicaldigestionandabsorptionChemicaldigestionandabsorptionRecallpolymersandmonomersHydrolysisHydrolysisisbreakingofabond‘withwater’ortheadditionofwaterDigestiveenzymeshydrolyzeonespecificsubstrateA-B-C-D+H2OA-B-H+OH-C-D

ABCDaseAbsorptionCarbohydrates-simple,hexosesugarswillbeabsorbedProteins-diortripeptidesaretypicallyabsorbed,alsoaminoacidsFats-Fattyacidsandmonoglyceridesareabsorbed(andthenconvertedimmediatelybacktotriglycerides)CarbohydratesSucrasecatalyzesthecleavageofthebondbetween(glucose-fructose)insucroseLactasecatalyzesthecleavageofthebondbetween(glucose-galactose)inlactoseMaltasecatalyzesthecleavageofthebondbetween(glucose-glucose)inmaltoseWheredowefindthesethreeenzymes?Enzymesaretransmembrane(oratleastmembrane-associated)proteinsFunctionatthemicrovilliofenterocytes(brushbordercells)ApicalsurfacebrushbordercellsSucraseMaltaseLactaseDisaccharidesinintestinallumeninteractwithbrushborderenzymes,andtheenzymaticproductsareabsorbedbrushbordercellsSucraseMaltaseLactaseSucroseMaltoseLactoseHexose

sugarsHexose

sugarsHexose

sugarsWhenbrushborderepithelialcellsfailtomakelactase….Lactoseisnotdigestedorabsorbed.BacteriafermentlactoseGas,diarrhea,etc.SucraseMaltaseLactaseAbsorptionofCarbsMonosaccharides(glucoseandgalactose)areintoepithelialcellmembranesviacotransport(alongwithNa+)Fructosemovesinvia

facilitateddiffusionAllmonosacs.pass

throughbasalmembraneofcell

(towardcapillary)by

facilitateddiffusionCo-transportAspecialtypeof

passivetransportMovesmorethanone

moleculeatsametime,

withmoleculesmovingin

samedirectionDoesn’tdirectlyrequireATP,butcellexpendsATPtomaintainhomeostasisCotransportcanfunctiondespiteanopposingconcentrationgradientExample-glucose/Na+co-transporterL

U

M

E

NCapillaryLactealAbsorbednutrientscanenteracapillaryoralactealSucroseMaltoseHexose

sugarsCarbsandpeptidesentercapillaries.Fatsenterlacteals.Animation-absorptionProteinDigestionEffectsofmastication(mechanicaldigestion)EffectsofpHonproteinstructureWhatenzymesarefirstinvolved?Wherearetheyfound?Whatenzymesareatbrushborder?Atbrushborder,trypsinogenisconvertedtotrypsinbyenterokinaseTrypsinthenactivates:chymotrypsin,elastaseandcarboxypepsidaseDipeptidasesatbrushborder!trypsinogentrypsinenterokinaseTrypsinactivates

pancreaticproteases.Dipeptidasesaremembraneenzymes.Dipeptidases!Activatespancreaticpeptidases.AbsorptionofproteinsAminoacidsareabsorbedbyFacilitateddiffusionCotransportOnceinsidethecellthey

transportedoutvia:FacilitateddiffusiondiffusionHepaticportal!DigestionoflipidsWhatenzymesareinvolved?Wherearetheyfound?LipidDigestionandAbsorptionFirstwithlipase