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TheDigestiveSystem(alsocalledthegastrointestinaloralimentarycanal)
TheprimaryfunctionsIngestionDigestionAbsorptionEliminationIntroductionAnatomically,thedigestivesystemconsistofa30-footlong,mucousmembrane-linedtubebeginningwithmouthandendingwiththeanus
ThedigestivesystemMouthPharynxEsophagusStomachSmallintestineLargeintestineLiverGallbladderPancreasAccessoryorgansofthedigestivesystem
TheoralcavityTheteethThetongueThepalateChewingandswallowingTheteethareusedtocut,tearandcrushfoodintosmallerpieces.Eachtoothconsistsofpulp,cementumandenamel.Theteethareclassifiedincisors,cuspidsandmolars.Thetonguemanipulatesfoodinthemouthduringmasticationanddeglutition.Thepalatethehardplateandthesoftplate(theuvulahangingfromthesoftplate)
Thepharynxorthroat,isalongmusculartubethatservesasapassagewayforfoodfromthemouthtotheesophagusandasapasswayforairfromnosetothewindpipe.Theesophagusisalongmusculartubeextendingfromthepharynxtothestomach.Foodispropelledbyrhythmiccontractionsofmusclesinthewalloftheesophagus.Thisprocessiscalledperistalsis.
ThestomachItiscomposedofanupperportioncalledfundus,amiddlesectionknownasthebodyandalowerportion,calledtheantrum.Thecardiacsphincterrelaxesandcontractstomovefoodfromtheesophagusintothestomach,whereasthepyloricsphincterallowsfoodtoleavethestomachwhenitsufficientlydigested.Asthestomachfills,therugaeunfolded,exposingthedigestiveglandsandstimulatingthemtosecretdigestiveenzymesandhydrochloricacid.Thesesubstanceshelptransformfoodpresenttoasemifluidsubstance.
Thesmallintestineistheregionofthegutwherenearlyallofthechemicaldigestionofthenutritioncomponentsoffoodtakeplace.Itdividedinto3sections:1)theduodenum2)thejejunum3)theileumInthewalloftheentiresmallintestinearemillionsofvilli.Itisthroughthecapillariesinthevillithatcompletelydigestednutrientspassintothebloodstreamandlymphvessels.
Thelargeintestineisdividedinto4parts:cecum,colon,sigmoidcolon,andrectum.Thececumisconnectedtothesmallintestinebytheileocecalvalve.Thecolonhas3divisions:theascendingcolon,thetransversecolon,thesigmoidcolon.Asfluidwastefromthesmallintestinepassthroughvarioussectionsofthecolon,waterisreabsorbedintobody.Therectumservesasareservoirforfeces.
Theliver:locatedintheupperrightquadrantofabdomen,producesbile.Besidesproducingbile,ithasseveralothervitalfunctions.Itmanufacturesbloodproteins,destorysolderythrocytesandreleasesbilirubin,removespoisons(detoxification)fromtheblood,storesandreleasesglycogenneededbythebody.
Thegallbladder:apear-shapedsacbehindthelowerportionoftheliver,storesbile,whichiscontinuouslysecretedbythehepaticcellsbetweenmeals.
Thepancreas:behindthestomach,manufacturesdigestivejuicecontainingenzyme(amylaseandlipase)thataidinthedigestionofproteins,starchesandfats.Italsosecretesinsulinandglucagon.
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