DIGESTIVE SYSTEM for B sc Nursing students

SYSTEM for B sc Nursing students

1. DIGESTIVESYSTEM
Digestionisdefinedasaprocessthatinvolvesphysicalandchemicalbreak
downofinsolublecomplexfoodmaterialsintosimplesolubleones.Digestivesystemis
madeupofgastroIntestinaltract(GIT)oralimentarycanalansaccessoryorgans,whichhelp
intheprocessofabsorptionandabsorption.GITisatubularstructureextendingfromthe
mouthuptoanuswithalengthofabout30feet.GITisformedby2typesoforgans.
1.PRIMARYDIGESTIVEORGANS:Whereactualdigestiontakesplace.Primary
digestiveorgansare:mouth,Pharynx,esophagus,stomach,smallintestineandlarge
intestine.
2.ACCESSORYDIGESTIVEORGANS:Helpstheprimarydigestiveorgansfortheprocess
ofdigestion.Theaccessorydigestiveorgansareteeth,tongue,salivaryglands,
exocrinepartsofpancreas,liverandgallbladder.
FUNCTIONSOFDIGESTIVESYSTEM
1.Ingestionorconsumptionoffoodsubstances.
2.Breakdownthemintosmallerones.
3.Transportofthesmallparticlestodifferentareasofthedigestivetract.
4.Secretionofnecessaryenzymesandothersubstancesfordigestion.
5.Digestionofthefoodparticles.
6.Absorptionofthedigestiveproducts.
7.Removalofunwantedsubstancesfromthebody.
PRIMARYMECHANISMSOFTHEDIGESTIVESYSTEM
Ingestion :Consumptionoffoodintothemouth.
Digestion :Agroupofprocessthatbreakcomplexmoleculesintosimplerones.
Motility :Movementbythemuscularcomponentsofthedigestivetract.
Secretion :Releaseofnecessaryenzymesandsubstancesfordigestion.
Absorption:MovementofdigestednutrientsthroughtheGITintothebloodandthe
internalenvironment.
Assimilation:Utilizationofabsorbedmaterialsbythecellsofthebody.
Elimination:Removalofunwantedsubstancesfromthebody.

2. HUMANDIGESTIVETRACT

3. MOUTHANDSALIVARYGLANDS
Oralcavityorbuccalcavityisformedbycheeks,lipsandpalate.Itenclosesthe
teeth,tongueandsalivaryglands.Digestivejuicepresentinthemouthissaliva,whichis
secretedbythesalivaryglands.
SALIVARYGLANDS
Inhumans,thesalivaissecretedby3pairsofmajorsalivaryglandsandsome
minorsalivaryglands.Themajorsalivaryglandsareparotid,submaxillaryorsub
mandibularandsublingualglands.Theminorsalivaryglandsarelingualmucousglands,
lingualserousglandsandbuccalglands.Salivaisamixtureofserousandmucousfluid
containingdigestiveenzymes.Ithelpstokeeptheoralcavitymoistandbeginstheprocess
ofchemicaldigestion.1000–1500mlsalivasecretedperday.
Thelargestofthesalivaryglandistheparotidgland.Itisaserousgland
locatedjustanteriortoeachear.Aparotidductenterstheoralcavityadjacenttothe
seconduppermolars.
Thesubmandibularglandsproducemoreserousthanmucoussecretions.
Thesubmandibularductsopenintotheoralcavityaneachsideofthefrenulumofthetongue.
Thesublingualglands,thesmallestofthe3pairedsalivaryglandsproduce
primarilymucoussecretions.Theyareimmediatelybelowthemucousmembraneinthe
flooroftheoralcavity.Eachsublingualglandhas10/12smallductsopeningintothefloor
oftheoralcavity.
FUNCTIONSOFSALIVA
Salivaisanessentialdigestivejuice,sinceithasmanyfunctions.
1.Helpsinswallowingandlubricatesthefood.
2.Salivabyitssolventactiondissolvesthesolidfoodsubstancesandstimulatestaste
budsforrecognitionoftaste.
3.Helpsinthedigestionofcarbohydratesbytheactionofcarbohydratedigesting
enzyme-salivaryamylaseorptyalin.
4.Duetoconstantsecretionofsaliva,themouthandteetharerinsedandkeptfreefrom
fooddebris;shedepithelialcellsandforeignparticles.Inthiswaysalivaprevents
bacterialgrowthbyremovingmaterialswiththehelpoflysozymeenzyme,whichplays
theantimicrobialactivity.
5.Bymoisteningandlubricatingsoftpartsofthemouthlikecheeks,lipsetc,salivahelps

4. inspeech.
6.Excretoryfunctioninthebodybyexcretingsomeviruseslikemumps,rabiesetc.
7.Regulatebodytemperatureandwaterbalance.
COMPOSITIONANDPROPERTIESOFSALIVA
Salivacontains99.5%waterand0.5%solids.SlightlyacidicwithpHof6.35–6.85.
SALIVA
REGULATIONOFSALIVARYSCRETION
Thesecretionofsalivaisregulatedbynervousmechanism.Salivaryglandare
underthecontrolofautonomicnervoussystemandreceiveefferentfibersfromboth
parasympatheticandsympatheticdivisionsofautonomicnervoussystem.
Whentheparasympatheticfibersofsalivaryglandsarestimulated,alarge
quantityofwaterysalivaissecreted.Theamtoforganicconstituentisless.Itisbecause
theparasympatheticfibersactivatetheacinarcellsanddilatethebloodvesselsofsalivary
glands.Theneurotransmitterisacetylcholine.
Thestimulationofsympatheticfiberscauseslesssecretionofsaliva.Whichis
Water(99.5%) Solids(0.5
%)
Organicsubstances
Inorganic
substances
Gases
Enzymes
Amylase,
maltase,lactoferritin,pospahatase,
kallikrein,carbonicanhydraseetc
linguallipase,
lysozyme,
Otherorganic
substances
Protein–Mucin&
albumin,bloodgroup
antigens,freeamino
Sodium,
calcium,
potassium,
Bicarbonate,
Chloride,
phosphateetc.
O2
CO2
N2

5. thickandrichinmucus.Itisbecauseofthesefibersactivatetheacinarcellsandcause
vasoconstrictionbysecretingnoradrenaline.
REFLEXREGULATIONOFSALIVARYSECRETION
Salivarysecretionisregulatedbynervousmechanismanditisareflex
phenomenon.Salivaryreflexesareof2types.1.Unconditionedreflexand2.Conditioned
reflex.
1.UNCONDITIONEDREFLEX
Inbornreflexthatispresentsincebirth.Thisreflexinducessalivarysecretionwhenany
substanceisplacedinthemouth.Itisduetothestimulationofnerveendingsinthe
mucusmembraneoftheoralcavity.
2.CONDITIONEDREFLEX
Acquiredbyexperience.Bythisreflexsalivarysecretionoccursbythesight,smell,hearing
orthoughtoffood.Itisduetotheimpulsesarisingfromeyes,nose,earetc.
STOMACH
Itisaholloworgansituatedjustbelowthediaphragmontheleftsideintheabdominal
cavity.Volumeofemptystomachis50ml.Undernormalconditions,itcanexpandto
accommodate1-1.5litresofsolidsandliquids.However,itiscapableofexpandingstill
furtherupto4liters.

6. Inhuman,stomachhas4parts:Cardiacregion,Fundus,Bodyorcorpus,Pyloricregion.
1.Cardiacregion:Itistheupperpartofthestomachwhereoesophagusopens.The
openingisguardedbyasphinctercalledcardiacsphincterwhichopensonlytowards
stomach.Thisportionisalsoknownascardiacend.
2.Fundus:Itisasmalldomeshapedstructure.Itiselevatedabovethelevelof
esophagealopening.
3.Bodyorcorpus:Itisthelargestpartofthestomachformingabout75-80%ofthe
wholestomach.Itextendsfromjustbelowthefundusuptothepyloricregion.
4.Pyloricregion:Ithas2parts,antrumandpyloricregion.Thebodyofthestomach
endsinantrum.Thejunctionbetweenbodyandantrumismarkedbyanangular
notchcalledincisuraangularis.
GLANDSOFSTOMACH
Theglandsofthestomacharethegastricglands,whicharetubularstructuremadeup
ofdifferenttypesofcells.2ormoregastricglandsjointogetherandopenintothestomach
cavityviagastricpits.Gasticglandsareclassifiedinto3typesonthebasisoftheirlocation
inthestomach.
1.Fundicglands:Situatedinbodyandfundusofstomach.
2.Pyloricglands:Presentinpyloricpartofthestomach.

7. 3.Cardiacglands:Locatedinthecardiacregiononthestomach.
FUNCTIONSOFGASTRICGLANDS
Functionofgastricglandistosecretegastricjuice.
FUNCTIONSOFSTOMACH
1.Storagefunction Mechanicalfunction,digestivefunction,Protective
function,Hemopoieticfunction,Excretory
function.
2.Formationofchyme
COMPOSITIONANDPROPERTIESOFGASTRICJUICE
Gastricjuice Vol:1200–1500ml/day
pH:0.9–1.2
GASTRIC
GLANDS
Water99.5% Solids0.5%
OrganicsubstancesInorganicsubstances
Enzymes Otherorganic

8. FUNCTIONSOFGASTRICJUICE
Digestivefunction:Thegastricjuiceactsmainlyonproteins.Theproteolytic
enzymesofthegastricjuicearepepsinandrennin.Gastriclipaseisaweaklipolytic
enzyme.
Hemopoieticfunction:Intrinsicfactorofgastricjuiceplaysanimportantrolein
erythropoiesis.Itisnecessaryforabsorptionofvit.B12fromGITintotheblood.
Protectivefunction:Thethickmucuspresentinthegastricjuiceisresponsibleforthe
protectionofgastricwall.
FunctionsofHcl:Itactivatespepsinogenintopepsin,Killssomeofthebacteria
enteringthestomachalongwithfoodsubstances–thisactioniscalledbacteriolytic
action,Provideacidmediumwhichisnecessaryfortheactionsofhormone.
REGULATIONOFSTOMACHSECRETION
Approximately2–3litersofgastricsecretionsareproducedperday.Bothnervousand
hormonalmechanismsregulategastricsecretions.TheneuronalmechanismsinvolveCNS
reflexesintegratedwithinthemedullaandhigherbraincentersinfluencethereflexes.Local
reflexesareintegratedwithintheintramuralplexusinthewallofdigestivetractanddonot
involveCNS.Regulationofstomachsecretioncanbedividedinto3phases.
1.Cephalicphase
2.Gastricphases
3.Intestinalphase
Cephalic(reflex)phase
Inthisphase,secretionofgastricjuicebythestimuliarisingfromhead.Thisphaseisunder
nervouscontrol.Duringthisphase,thegastricsecretionoccursevenwithoutthepresence

9. offoodinthestomach.ThegastricjuicesecretedduringthisphaseiscalledAppetitejuice
andislessinquantitybutrichinenzymesandHCl.
Thisphasebeginseitherwhenfoodisplacedinthemouthorwhenapersonthinks,
smells,seesorhearsaboutfood.Whenfoodisplacedinthemouth,itstimulatessaliva
secretion.Simultaneously,itstimulatesthetastebudsandotherreceptorsinthemouth
whichsendsensoryimpulsestothebrain.Motorimpulsesfromthebrainpassthroughthe
vagusnervewhichstimulatesgastricglandstoincreasethesecretion.Thistypeofreflexis
calledUnconditionedreflex.
Thesight,smell,hearingorthoughtoffoodinducessalivasecretionandimpulsesfrom
thesesensoryorgansstimulatesthecerebralcortexwhichsendsmotorimpulsestothe
vagusnervetherebystimulatinggastricsecretion.ThistypeofreflexiscalledConditioned
reflex.
sight,aroma,taste,thought----->hypothalamusgustatorycenters----->vagal
nucleiofmedulla----->vagusnerve(parasympathetic)----->increasedgastric
secretion.
Gastricphase
Thesecretionofgastricjuicewhenfoodentersthestomach,itiscalledgastricphase.Itis
underbothnervousandhormonalcontrol.Thegastricjuicesecretedinthisphaseisrichin
pepsinogenandHcl.Themechanismsinvolvedinthisphaseare:-
1.Nervousmechanismthroughmyentricreflexandvagovagalreflex
2.Hormonalmechanismthroughgastrin.
Thestimuliwhichinitiatethismechanismsare–Distensionofstomach,mechanical
stimulationofgastricmucosabybulkoffoodandchemicalstimulationofgastricmucosaby
thefoodcontents.
foodreachesthestomach-------->neuralmechanism,hormonalmechanism,distention
&lowacidity--->digestedproteins--->vagalafferentstomedulla--->increaseinpH--->vagal
efferentstostomach--->gastrinreleased--->parasympatheticAChrelease--->enzymes&
HClreleased-->increasedgastricsecretion
controlofHClsecretingparietalcells
gastrin,histamine,&AChincreasethereleaseofHClfromparietalcells
H+comesfromcarbonicacidrelease
Intestinalphase
Thisphaseiscontrolledbytheentranceofacidicchymeintotheduodenum.Thepresence
ofchymeintheduodenuminitiatesbothneuralandhormonalmechanismswhichfirst

10. stimulateandtheninhibitgastricsecretions.WhenpHofchymeis3orabovethe
stimulatoryresponseoftheintestinalphaseisgreatest.Gastrinreleasedfromthe
duodenumratherthanfromthestomachiscarriedinthebloodtothestomach,whereit
stimulatesgastricsecretions.CNSalsoincreasegastricsecretionduringthisphase.
WhenpHofchymeis2orbelow,inhibitoryimpulseisgreatest.Thehormone,secretin
whichinhibitssecretionsandisreleasedfromduodenum.Fattyacidsandotherlipidsinthe
duodenuminitiatethereleaseof2hormonescholecytokinin–pancreozyminandGastric
Inhibitorypolypeptide(GIP)thatalsoinhibitsgastricsecretions.Acidicchymeinduodenum
alsoinitiatesCNSandlocalreflexestoinhibitgastricsecretions.
excitatoryphaseinhibitoryphase-->chymeenterstheduodenum->inhibitionof
vagalnuclei--->releaseofintestinalgastrin->inhibitionoflocalreflexes
continuedgastricsecretionactivationofsympathetics--->releaseofinhibitory
hormone:(secretin,cholecystokininCCK,gastricinhibitorypeptideGIP).
INTERDIGESTIVEPHASE:Secretionofsmallamountofgastricjuiceinbetweenmeals(or
duringtheperiodoffasting)iscalledinterdigestivephase.Gastricsecretionduringthis
phaseismainlyduetothehormoneslikegastrin.Alcoholandcaffeine,increasesthegastric
secretionbystimulatinggastricmucosa.
PANCREAS
Pancreasisadualorganhaving2functions,theendocrinefunctionsandtheexocrine
function.Theendocrinefunctioninvolvesproductionofthehormones.Theexocrine
functioninvolvesthesecretionofpancreaticjuice.
FUNCTIONSOFPANCREATICJUICE
Pancreaticjuicehasdigestivefunctionandneutralizingactions.
1.Digestionofproteins:Themajorproteolyticenzymesinthepancreaticjuicearetrypsin
andchymotrypsin.Otherproteolyticenzymesarecarboxypeptidase,nuclease,
elastaseandcollagenase.
2.Digestionoflipids:Thelipolyticenzymespresentinpancreaticjuicearepancreatic
lipase,cholesterolesterhydrolase,phospholipaseA&B.
3.Digestionofcarbohydrates:Pancreaticamylaseistheamylolyticenzymepresentin
pancreaticjuice.Likesalivaryamylase,thepancreaticamylasealsoconvertsstarch

11. intodextrinandmaltose.
4.Neutralizingactionofpancreaticjuice:Whenacidchymeentersintestinerrom
stomach,pancreaticjuicewithlargequantityofbicarbonateisreleasedintointestine.
Itmakesthepancreaticjuicehighlyalkaline.Thisalkalinepancreaticjuiceneutralizes
acidityofchymeintheintestine.Neutralizingactionisanimportantfunctionof
pancreaticjuice,becauseitprotectstheintestinefromthedestructiveactionofacidic
chyme.
COMPOSITIONANDPROPERTIESIFPANCREATICJUICE
Pancreaticjuice Vol:500–800ml/day
pH:8–8.3
Water99.5% Solids0.5%
OrganicsubstancesInorganicsubstances
Sodium,Calcium,Pottassium
Magnesiu,Bicarbonate,
chloride,Phosphate,Sulphate.
Enzymes Otherorganicsubstances
(albuminandglobulin)
Proteolyticenzymes
Trypsin
Chymotrypsin
Carboxypeptodase
Nuclease
Ellastase
Collaginase
Lipolyticenzymes
Pancreaticlipase
PhospholipaseA
PhospholipaseB
Colipase
Bilesaltactivatedlipase
Amylolyticenzymes
Pancreaticamylase

12. REGULATIONOFPANCREATICSECRETION
1.parasympathetic-causesreleaseduringcephalicandgastricphasesofgastric
secretion
2.secretin-hormonethatcausesreleaseof"bicarbonate-rich"pancreaticjuicesin
responsetothepresenceofHCl
3.cholecystokinin-hormonethatcausesreleaseof"enzyme-rich"pancreaticjuicein
responsetothepresenceofproteinsandfats.
LIVERANDGALLBLADDER
Liveristhedualorganhavingbothsecretaryandexcretoryfunctions.Itisthelargest
glandinthebodyweighingabout1.5kginman.Itislocatedintheupperandrightsideofthe
abdominalcavityimmediatelybeneathdiaphragm.
COMPOSITIONOFBILE
Bile
Volume:800–1200ml
pH:8–8.6
Water(97.6%) Solids(2.4%)
Organicsubstances Inorganicsubstances
Bilesalts Sodium
Bilepigments Calcium
Cholesterol Potassium
Fattyacids Chloride
Lecithin Bicarbonate
Mucin
SECRETIONOFBILE
Bileissecretedbyhepatocytes.Theinitialbilesecretedbyhepatocytes,itcontain
largequantityofbileacids,bilepigments,cholesterol,lecithinandfattyacids.From
hepatocytes,bileisreleasedintocanaliculi.Fromherethebileentersthecommonhepatic

13. ductbypassingthroughsmallductsandhepaticducts.Fromcommonhepaticduct,bileis
divertedeitherdirectlyintotheintestineorintogallbladderwhereitisstored.
Sodium,bicarbonateandwaterareaddedtobilewhenitpassesthroughtheducts.
Thesesubst6ancesaresecretedbytheepithelialcellsoftheducts.Thusadditionof
sodium,bicarbonate,andwaterincreasesthetotalquantityofbile.
STORAGEOFBILE
Mostofthebilefromtheliverentersthegallbladderwhereitisstored.Itisreleased
fromgallbladderintotheintestinewheneveritisrequired.Whenbileisstoredingall
bladderitundergoesmanychangesbothinqualityandquantitysuchas:
Alargeamountofwaterandelectrolytesareabsorbedresultinginhigh
concentrationofbilesalts,bilepigments,cholesterol,fattyacidsandlecithin.
ThepHandspecificgravityofbilearealteredingallbladder.
Someamountofmucinisaddedtobile.
BILESALTS:Thesearethesodiumandpotassiumsaltsofthebileacids,whichare
conjugatedwithglycineortaurine.
FUNCTIONSOFBILE
Bilesaltsinbilearerequiredfordigestionandabsorptionoffatsintheintestine.
Thebilesaltscombinewithfatsandmakecomplexesoffatscalledmicelles.The
fatsintheformofmicellescanbeabsorbedeasily.
Bilepigmentsarethemajor3excretoryproductsofthebile.
Bilesaltactaslaxatives.Laxativeisanagentwhichinducesdefecation.
Bileinhibitsthegrowthofcertainbacteriainthelumenofintestinebyitsnatural
detergentaction.
Bilesaltsstimulatethesecretionofbilefromliver;thisactioniscalledcholereticaction.
ItmaintainsanoptimumpHfortheactionofdigestiveenzymes.
Itpreventstheformationofgallstones.
Themucininbileactsasalubricantforthechimeinintestine.
Itactasacholagogue,isanagentwhichincreasesthereleaseofbilefromgallbladder.
FUNCTIONSOFLIVER
Liveristhelargestglandandoneofthevitalorgansofthebody.Itpreparesmany

14. vitalmetabolicandhomeostaticfunctions,whichare:
2.STORAGEFUNCTION:Manysubstanceslikeglycogen,aminoacids,iron,folicacidand
vitA,B12&Darestoredinliver.
3.METABOLICFUNCTION:Metabolismofcarbohydrates,proteins,fats,vitaminsand
manyhormonesiscarriedoutinliver.
4.SYNTHETICFUNCTION:LiverProducesglucosebygluconeogenesis.Italso
synthesizessteroids,somatomedinandheparin.
5.SECRETORYFUNCTION:Bileisthesecretaryproductofliver.
6.EXCRETORYFUNCTION:Liverexcretescholesterol,bilepigments,heavymetals,toxins,
bacteriaandvirusthroughbile.
7.HEATPRODUCTION:Enormousamountofheatisproducedinliverbecauseofthe
metabolicreaction.
8.HEMOPOIETICFUNCTION:Infetus,liverproducesthebloodcells.
9.HEMOLYTICFUNCTION:ThesenileRBCsafterthelifespanof120daysaredestroyed
byREcellsofliver.
10.INACTIVATIONOFHORMONESANDDRUGS:thefatsolubledrugsareconvertedinto
watersolublesubstances,whichareexcretedthroughbileorurine.
11.DEFENSIVEANDDETOXIFICATIONFUNCTION:TheREcellsoftheliverplayan
importantroleinthedefenseofthebodybydetoxification.
REGULATIONOFBILESECRETION
Bilesecretionisacontinuousprocessthroughtheamountmaybelessduringfasting.
Itincreases3hrsaftermeals.Thesecretionofbilefromtheliverandreleaseofbile
fromthegallbladderareinfluencedbysomechemicalfactorswhicharecategorizedinto
3groups.
CHOLERETICS:Substances,whichincreasethesecretionofbilefromliver,areknownas
choleretics.Ex:Ach,Secretinetc.
CHOLAGOGUES:Itisanagent,whichincreasesthereleaseofbilefromgallbladderintothe
intestine.Ex:Bilesalts,Calciumetc.
HYDROCHLORETICAGENTS:Thiscausessecretionofbilefromliverwithlargeamtofsolids
andwater.Ex:HCl.
GALLBLADDER
Thebilesecretedfromliverisstoredingallbladder.Thecapacityofgallbladderis

15. approximately50ml.Themajorfunctionsofgallbladderarethestorageand
concentrationofbile.
3.Storageofbile.
4.Concentrationofbile.
5.AlterationofpHofbile.
6.Secretionofmucin.
7.Maintenanceofpressureinbiliarysystem.
JAUNDICEORICTERUS
Itisaconditioncharacterizedbyyellowcoloroftheskin,mucusmembraneanddeeper
tissuesduetoincreasedbilirubinlevelintheblood.Thenormalserumbilirubinlevelis
0.5-1.5mg/dl.Jaundiceoccurswhenbilirubinlevelexceeds2mg/dl.Jaundiceis
classifiedinto3types.
PREHEPATICORHEMOLYTICJAUNDICE:Itoccursbecauseofexcessive
destructionofRBCsresultinginincreasedbloodleveloffreebilirubin.Any
conditionthatcauseshemolyticanemiacanleadtohemolyticjaundice.
HEPATICORHEPATOCELLULARORCHOLESTATICJAUNDICE:Itoccursdueto
thedamageofhepaticcells.Becauseofthedamage,theconjugatedbilirubin
fromlivercannotbeexcretedanditreturnstoblood.Causesincludeviral
hepatitis,alcoholichepatitis,livercirrhosis.
POSTHEPATICOROBSTRUCTIVEOREXTRAHEPATICJAUNDICE:Thistypeof
jaundiceoccursbecauseoftheobstructionofbileflowatanylevelofthebiliary
system.Thebilecannotbeexcretedintothesmallintestine.So,bilesalts
andbilepigmentsenterthecirculation.Causesincludegallstones,cancerof
biliarysystemorpancreas.
SMALLINTESTINE
SmallintestineisthepartoftheGITextendingbetweenthepyloricsphincterof
stomachandileocecalvalve,whichopensintolargeintestine.Itiscalledsmall
intestinebecauseofitssmalldiametercomparedtothatoflargeintestine.Butitis
longerthanlargeintestine.Itslengthisabout6meters.Maximumabsorptionof
digestedfoodproductstakesplacehere.Smallintestineconsistsof3portions.
1.Proximalpartknownasduodenum.
2.Middlepartknownasjejunum.

16. 3.Distalpartknownasileum.
Secretionfromsmallintestineiscalledsuccusentericus.
FUNCTIONSOFSUCCUSENTERICUS
DIGESTIVEFUNCTION:Theenzymesofsuccusentericusactonthepartially
digestedfoodandconvertthemintofinaldigestiveproducts.
PROTECTIVEFUNCTION:Themucuspresentinthesuccusentericusprotectthe
intestinalwallfromtheacidchime,whichenterstheintestinefromstomach:there
byitpreventsintestinalulcer.
ACTIVATORFUNCTION:Theenterokinasepresentinintestinaljuiceactivates
trypsinogenintotrypsin.Trypsininturnactivatesotherenzymes.
HEMOPOIETICFUNCTION:Theintrinsicfactorofcastle,whichplaysanimportant
roleinerythropoiesis.
HYDROLYTICPROCESS:Intestinaljuicehelpsinalltheenzymaticreactionsof
digestion.
COMPOSITIONOFSUCCUSENTERICUS
Succusentericus Volume:
1800ml/day
pH :8.3
Water99.5% Solids0.5%
OrganicsubstancesInorganicsubstances
Sodium, calcium, potassium,
bicarbonateetc
EnzymesOtherorganicsubstances
Mucus,intrinsicfactor&defensins
Proteolyticenzymes Lipolyticenzymes Amylolyticenzymes
Enterokinase

17. REGULATIONOFSECRETIONSUCCUSENTERICUS
Thesecretionofsuccusentericusisregulatedbybothnervousandhormonal
mechanisms.
NERVOUSMECHANISM
Stimulationofparasympatheticnervescausesvasodilationandincreasethesecretion
ofsuccusentericus.Stimulationofsympatheticnervescausesvasoconstrictionand
decreasesthesecretionofsuccusentericus.But,theroleofthesenervesintheregulation
ofintestinalsecretioninphysiologicalconditionisuncertain.
Whenchymeentersthesmallintestine,themucosaisstimulatedbytactilestimulior
irritation.Itcausesdevelopmentoflocalnervousreflexes,whichstimulatetheglandsof
intestine.

18. HORMONALREGULATION
Whenthechymeentersthesmallintestine,theintestinalmucosasecreteenterokinin,
secretinandcholecytokinin.Whichpromotethesecretionofsuccusenterokinaseby
stimulatingtheintestinalglands.
LARGEINTESTINE
Thelargeintestineisalsoknownascolon.Itextendsfromileocecalvalveuptoanus.
ThelargeintestinaljuiceisawateryfluidwithpHof8.0.
COMPOSITIONOFLARGEINTESTINALJUICE
Largeintestinaljuice
Water99.5% Solids0.5%
Organicsubstances Inorganicsubstances
Albumin Sodium
Globulin Calcium
Mucin Potassium
Urea Bicarbonate
Debrisofepithelialcells Chloride
Phosphate
Sulphate
FUNCTIONLARGEINTESTINALJUICE
NEUTRALIZATIONOFACIDS:Strongacidsformedbybacterialactioninlargeintestineare
neutralizedbythealkalinenatureoflargeintestinaljuice.Thealkalinityofthisjuiceismainly
duetothepresenceoflargequantityofbicarbonate.
LUBRICATIONACTIVITY:Themucinpresentinsecretionoflargeintestinelubricatesthe
mucosaoflargeintestineandthebowelcontents.Sothatthemovementofbowelis

19. facilitated.
FUNCTIONSOFLARGEINTESTINE
1.Absorptivefunction(water,electrolytes,alcoholetc)
2.Formationoffeces
3.Excretoryfunction(Heavymetals,mercury,lead,bismuth)
4.Secretoryfunction(mucinandinorganicsubstanceslikechloride&bicarbonate)
5.Syntheticfunction
MOVEMENTSOFGASTROINTESTINALTRACT
MASTICATION
MasticationorchewingisthefirstmechanicalprocessintheGITbywhichthefood
substancesarecutintosmallparticlesandcrushedorgroundintoasoftbolus.The
significanceofmasticationincludes,
8.Breakdownoffoodstuffsintosmallerparticles.
9.Mixingofsalivawithfoodsubstancesthoroughly.
10.Lubricationandmoisteningofdryfoodbysalivasothat,theboluscanbeeasily
swallowed.
11.Appreciationoftasteofthefood.
DEGLUTTITION
Deglutitionorswallowingistheprocessbywhichfoodispassedfrommouthto
stomach.Ithas3stages:
1.Oralstage:inthisstage,foodenterpharynxfrommouth.Itisavoluntarystage.
a.Thebolusisplacedoverpostero-dorsalsurfaceofthetongue.Itiscalledthe
preparatoryposition
b.Theanteriorpartofthetongueisretractedanddepressed.
c.Theposteriorpartofthetongueiselevatedandretractedagainsthardpalate.This
pushesthebolusbackwardsintothepharynx
d.Thenforcefulcontractionoftongueagainstthepalateproducesapositivepressureinthe
posteriorpartoftheoralcavity
Pharyngealphase:Thisphaseisareflexthatisinitiatedbystimulatingthereceptorsinthe
oropharynx. Bolusispushedintothepharynxbythetongueandatthistimethesoft

20. palateelevatestoclosethepassagebetweenoropharynxandnasoparynx.Theepiglottis
closesthelaryngealopeningtoprevententryoffoodintorespiratorypassage.Thereflex
relaxationoftheupperesophagealsphincterandthebolusmovetotheesophagus.During
thisphasetherespirationremainsstopped.
Esophagealphase:Whenthebolusreachestheupperendofesophagus,theupper
esophagealsphinctercontractsandbolusmovetowardsthebodyofesophagus.Thisisthe
primaryperistalsis,andhelpstosendthebolustothestomachwiththehelpofgravity.Ifit
failsandbolusremainsintheesophagus,andthenduetostretchingofbolussecondary
peristalticwavestartinthewallofesophagusandthebolusiscarriedtothestomach.The
relaxationofloweresophagealsphincterhelpsintothemovementofbolustothestomach
fromesophagus.
MOVEMENTSINSTOMACH:
Theseareduetothecontractionofsmoothmusclespresentinitswall.Whenthe
stomachisempty,itproducessomemovementsorcontractionscalledhungercontractions
whichareslightlypainful.Theyaremainlyduetothepressurechangesinthestomach.
Digestiveperistalsisisthetypeofmovementsinthestomach.Thesemovementsstart
assoonasfoodentersintothestomach.Themovementsinitiallyisintheformofsmall
inclentationofthewallbutsoonencirclesthemidpartofthestomachintheformofring
constrictionwhichthenproceedslikeawavetowardsthepylorus.Initially,thecontractionis
week,butgraduallyitincreasesinstrengthinthepylorusitbecomesstrongenoughtobisect
thecavityofstomach.Thesewavesofcontractionoccurregularlyattherateof3/minand
suchcontractionsarealsoresponsibleforgastricemptying.Duringthisdigestiveperistalsis,
fundusremainssilent.
GastricEmptying:
Itisdefinedastheprocessbywhichthestomachemptiesitscontentsintotheduodenum.
Whendigestiveperistalsisreachestheendofthestomachthepylorusandduodenum
contracttogether.Butbeforetheperistalsisfullyreachesthepylorus,asmallpartofthe
chymepassesintoduodenumduetothecontractionofbodyofstomach.Inthenext
moment,whentheperistalsisreachesfullytothepylorus,majorpartofthechymeisthrown
backforcefullyintothecavityofstomachduetocontractionofpylorus.Theretropulsion
alongwiththegrindingactionofpyloriccontractionsconvertsthegastriccontentstothe
chyme.

21. MOVEMENTSINSMALLINTESTINE:
Mixingmovements
a.Segmentalcontractions:
b.Pendularmovements
Propulsivemovements:Peristalsis
a.SegmentalContractions:Itisthemixingmovementswhichitmixesthechymewiththe
digestivejuicesinthesmallintestine.Ithelpsinabsorptionbybringingnewerareasof
chymeincontactwiththemucousmembrane.
Inthismovements,severalconstrictionoccursimultaneouslyalongthelengthofthe
intestinewhichdividesintheintestineintonumeroussegments.Inthenextmomentfresh
constrictionappearthepreviouslyuncontractedportionssothatthecontentsaresubdivided.
Pendularmovements:Thistypeofmovementhelpsinmixingandsharingofintestinal
contents.Inthismovement,alongsegmentofintestineslipsoveritscontentsto–
and-frowiththeregularityofthependulum,andhencearecalledpendular
movements.
2.Peristalsis:Itisapropulsivemovementfoundinmanytubularorganswithsmooth
muscleattheirwallslikegut,ureter,fallopiantubesetc.,Peristalsiscarriesthecontentsof
thetubeforwardthroughthelumen.PeristalsisishighlyusefulinGITasit
1.Movesthechymeforwardsothatitisexposedtodifferentdigestivejuices.
2.Forwardmovementofchymealsohelpsintheabsorptionwhichcanoccuralongthewhole
lengthoftheintestine.
ItpreventsbacterialgrowthinSIbycontinuouslypushingthecontentsdowntothecolon.
Augmentbloodandlymphflowandithelpsabsorptionfromintestine.
Parasympatheticnervestimulateandsympatheticnerveinhibitperistalsis.Chemicalslike
gastrin,CCK–PZ,serotoninincreasesandsecretindecreasesperistalsis.
MOVEMENTSOFVILLI
Intestinalvillishows2typesofmovements
Lashingmovement:Villimovelikewhipcuttingthroughthechyme.
Pumpingmovement:m:Alternateshorteningandlengtheningoccurs.
Villidonotmoveinemptystomach.MovementofvilliareimportantforabsorptioninSI.
Theileo–cecalsphincteratthejunctionofileumandlargeintestineremainsmildly
contractedmostofthetimebutperistalsiscontractionreachingtheileo–cecalsphincter

22. fromSIcausesittorelaxandallowmovementofchymefromSIintotheCecum.Valve
preventsthebackflowofchymefromcecumtoSmallintestine.
MOVEMENTSOFLARGEINTESTINE:
Inthecolonchymeisconvertedintofeces.Absorptionofwaterandsalts,thesecretion
ofmucusandextensiveactionsofmicroorganismsareinvolvedintheformationoffeces.
Thecolonstoresthemuntiltheyareeliminatedbyaprocesscalleddefecation.Largepartof
thecolonundergoesstrongmovementcalledmassperistalsis,whicharethemodifiedform
ofperistalsis.Intheselargesegmentofcoloncontractatatimeandthuspushesthe
contentsforcefullytowards.Thecontentsreachestherectumtogiverisetodesirefor
defecation.
DEFECATION:
Itistheprocessbywhichthefecalmatterisexpelledtotheexterior.Inthisprocessthe
fecesenterstherectumduetomassperistalsisandthedesirefordefecationfeltduetorise
ofintrarectalpressureaconsequentstretchingofrectalwall.Whendesireisattended
persontakesasuitableposture,suitableplaceandvoluntaryrelaxationofexternalsphincter
occurwherebythefecesisexpelledout.Rectalstretchingstimulatecoloncontraction,thus
morefecesisexpelled.Afteracompletedefecation,majorpartofdistalcolonisevaccuated
.
Ifthedesireisnotattended,thereisastrongvoluntarycontractionoftheexternal
sphincter.Aftersometimethedesireisautomaticallylost.Ifthisiscontinuedforalong
timebowelhabitbecomesirregularandthepersonmaysufferfromconstipation.
ComponentsofFeces:25%waterand75%solids.Solidportionconsistsoforganic
andinorganicconstituents.
DIGESTION&ABSORPTION:
Inthemouth,salivaryamylaseconvertsstarchtomaltose,maltotrioseandα-
dextrins.Inthestomach,pepsinconvertsproteinstopeptidesandlingualandgastric
lipasesconvertsometriglyceridesintofattiacids,diglyceridesandmonoglycerides.Thus
chymeenteringtheSIcontainspartiallydigestedcarbohydrates,proteinsandlipids.The
completionofthedigestionofcarbohydrates,proteinsandlipidsareacollectiveeffortof
pancreaticjuice,bileandintestinaljuiceintheSI.
Digestion&absorptionofcarbohydrates:-
Salivaryamylasemaycontinueinstomachforawhile,theacidicpHofthe

23. stomachdestroyssalivaryamylaseandendsitsactivity.Thus,afewstarchesarereduced
tomaltose.Butsomestarchesarenotbrokenandisenterintopancreaticjuice.Itactsin
thesmallintestine.Amylasenotactincellulose(indigestibleplantfiber).Thissplittingis
takeplaceonlybythepresenceofbrushborderenzymescalledα–dextrinase.
α-dextrin α-dextrinase Glucose
Starch Amylase Cellulose
Sucrose1 Glucose+Fructose
Lactose2 Glucose+Galactose
Maltose3 Glucosemolecules
1-Sucrase
2-Lactase
3-Maltase
Insomepeoplethemucosalcellsofthesmallintestinefailtoproduceenough
lactase,whichisessentialforthedigestionoflactase.Thisresultsinaconditioncalled
lactaseintolerance,inwhichundigestedlactoseinchymeretainsfluidinfeces,andbacterial
fermentationoflactoseresultsintheproductionofgases.Symotmsincludediarrhea,gas,
abdominalcrampsafterconsumptionofmilkandotherdairyproducts.
PassageofthedigestednutrientsfromtheGItractintothebloodorlymphis
calledAbsorption.Absorptionofmaterialsoccursviadiffusion,facilitateddiffusion,
osmosisandactivetransport.About90%absorptionofnutrientsoccursinthesmall
intestine.Other10%occurinthestomachandlargeintestine.
Absorptionofmonosaccharides:-Monosaccharidespassesfromthelumenthroughthe
apicalmembraneviafacilitateddiffusionoractivetransport.Fructose(monosaccharides
foundinfruits)istransportrdviafacilitateddiffusion.Glucoseandgalactoseare
transportedintoepithelialcellsofthevilliviasecondaryactivetransportthatiscoupledtothe
activetransportofNa+.Thetransporterhasbindingsitesforoneglucosemoleculeand
2Na+.Monosaccharidesthenmoveoutoftheepithelialcellsthroughtheirbasolateral
surfaceviafacilitateddiffusionandenterthecapillariesofthevilli.
AbsorptionofAminoacids,DipeptidesandTripeptides:-Mostproteinsareabsorbedas
aminoacidsviaactivetransportprocessthatoccurmainlyintheduodenumandjejunum.

24. Abouthalfoftheabsorbedaminiacidsarepresentinfood,whereastheotherhalfcomefrom
proteinsindigestivejuices.SomeaminoacidsenterepithelialcellsofthevilliviaNa+-
dependentsecondaryactivetransportthataresimilartotheglucosetransporter.Both
aminoacidsandmonosaccharidesaretransportedinthebloodtotheliverbywayofthe
hepaticportalsystem.
AbsorptionofLipids:-Alldietarylipidsareabsorbedviasimplediffusion.Adultsabsorbs
about90%ofthelipidspresentintheSIduetotheirlowerproductionofbile,whereasnew
bornorinfantsabsorbonlyabout85%oflipids.
Thelipiddigestionactedbytheemulsificationprocessandresults
monoglyceridesandfattiacids.Thelingualandpancreaticlipaseremovethetwoofthe
threefattiacidsfromglycerolduringdigestionofatriglycerides,theotherfattiacidsremains
attachedtoglycerolformingmonoglyceride.Thesmallamountofshortchainfattiacidsin
thedietpassesintotheepithelialcellsviasimplediffusionandfollowsabloodcapillaryofa
villus.Bilesaltsareamphipathic,theyhavebothpolar(hydrophillic)andnonpolarportions.
Thustheycanformmicellsofabout2–10nmdiametercontainingbilesalts.Thepolar
portionofbilesaltsattheirsurfacesoitcandissolvethewaterofintestinalfluid.When
chymereachestheileumthebilesaltsreabsorbedreturnedbybloodtotheliverthrough
Hepaticportalsystem.Thiscycleofbilesaltsecretioniscalledtheenterohepaticcirculation.
Whenlipidsarenotabsorbedproperlythefatsolublevitaminsarenotabsorbedinadequately.