The Digestive System Name:_________________________________________Class:__________Date:____________

Vocabulary

Term Definition esophagus Narrowtubethatcarriesfoodfromthethroattothestomach.large intestine

Widetubeinwhichwaterisextractedtoformfeces;connectsthesmallintestinewiththeanus.

peristalsis Musclecontractionsthathelpfoodmovethroughthedigestivesystem.small intestine

Narrowtubeinwhichfurtherdigestionandabsorptiontakesplace;startsatthestomachandendsatthelargeintestine.

stomach Sac-likeorganattheendoftheesophaguswheremuchofthedigestiveprocesstakesplace.

villi Small,finger-likeprojectionsofthesmallintestinethatincreasesurfaceareaforabsorption.

How many organs of the digestive system can you name? Stomach?Mouth?Ittakesmanydifferentorgansworkingtogetherinordertodigestyourfood.Somearepartofthepipelinethatfoodpassesthrough.Othersmakespecialchemicalsthatareneededfordigestion. Organs of the Digestive System Themouthandstomacharejusttwooftheorgansofthedigestivesystem.Otherdigestivesystemorgansaretheesophagus,smallintestine,andlargeintestine.Below,youcanseethatthedigestiveorgansformalongtubeInadults,thistubeisabout30feetlong!Atoneendofthetubeisthemouth.Attheotherendistheanus.Foodentersthemouthandthenpassesthroughtherestofthedigestivesystem.Foodwasteleavesthebodythroughtheanus.Thisdiagramtotheleftshowstheliver,gallbladder,andpancreas.Theseorgansarepartofthedigestivesystem.Fooddoesnotpassthroughthem,buttheysecretesubstancesneededforchemicaldigestion.Theorgansofthedigestivesystemarelinedwithmuscles.Themusclescontract,ortighten,topushfoodthroughthesystem(Figurebelow).Themusclescontractinwaves.Thewavespassthroughthedigestivesystem

likewavesthroughaslinky.Thismovementofmusclecontractionsiscalledperistalsis.Withoutperistalsis,foodwouldnotbeabletomovethroughthedigestivesystem.Peristalsisisaninvoluntaryprocess,whichmeansthatitoccurswithoutyourconsciouscontrol.Thisdiagramshowshowmusclespushfoodthroughthedigestivesystem.Musclecontractionstravelthroughthesysteminwaves,pushingthefoodaheadofthem.Thisiscalledperistalsis.Theliver,gallbladder,andpancreasarealsoorgansofthedigestivesystem.Fooddoesnotpassthroughthesethree

organs.However,theseorgansareimportantfordigestion.Theysecreteorstoreenzymesorotherchemicalsthatareneededtohelpdigestfoodchemically. Mouth, Esophagus, and Stomach Themouthisthefirstorganthatfoodenters.Butdigestionmaystartevenbeforeyouputthefirstbiteoffoodintoyourmouth.Justseeingorsmellingfoodcancausethereleaseofsalivaanddigestiveenzymesinyourmouth.Onceyoustarteating,salivawetsthefood,whichmakesiteasiertobreakupandswallow.Digestiveenzymes,includingtheenzymeamylase,startbreakingdownstarchesintosugars.Yourtonguehelpsmixthefoodwiththesalivaandenzymes.Yourteethalsohelpdigestfood.Yourfrontteetharesharp.Theycutandtearfoodwhenyoubiteintoit.Yourbackteetharebroadandflat.Theygrindfoodintosmallerpieceswhenyouchew.Chewingispartofmechanicaldigestion.Yourtonguepushesthefoodtothebackofyourmouthsoyoucanswallowit.Whenyouswallow,thelumpofchewedfoodpassesdownyourthroattoyouresophagus.Theesophagusisanarrowtubethatcarriesfoodfromthethroattothestomach.Foodmovesthroughtheesophagusbecauseofperistalsis.Atthelowerendoftheesophagus,acircularmusclecontrolstheopeningtothestomach.Themusclerelaxestoletfoodpassintothestomach.Thenthemusclecontractsagaintopreventfoodfrompassingbackintotheesophagus.Somepeoplethinkthatgravitymovesfoodthroughtheesophagus.Ifthatweretrue,foodwouldmovethroughtheesophagusonlywhenyouaresittingorstandingupright.Infact,becauseofperistalsis,foodcanmovethroughtheesophagusnomatterwhatpositionyouarein—evenupsidedown!Justdon’ttrytoswallowfoodwhenyouareupsidedown—youcouldchoke!Thestomachisasac-likeorganattheendoftheesophagus.Ithasthickmuscularwalls.Themusclescontractandrelax.Thismovesthefoodaroundandhelpsbreakitintosmallerpieces.Mixingthefoodaroundwiththeenzymepepsinandotherchemicalshelpsdigestproteins.Water,salt,andsimplesugarscanbeabsorbedintothebloodfromthestomach.Mostothersubstancesarebrokendownfurtherinthesmallintestinebeforetheyareabsorbed.Thestomachstoresfooduntilthesmallintestineisreadytoreceiveit.Acircularmusclecontrolstheopeningbetweenthestomachandsmallintestine.Whenthesmallintestineisempty,themusclerelaxes.Thisletsfoodpassfromthestomachintothesmallintestine. Small Intestine Thesmallintestineaisnarrowtubethatstartsatthestomachandendsatthelargeintestine(Figureabove).Inadults,thesmallintestineisabout23feetlong.Chemicaldigestiontakesplaceinthefirstpartofthesmallintestine.Manyenzymesandotherchemicalsaresecretedhere.Thesmallintestineisalsowheremostnutrientsareabsorbedintotheblood.Thelatersectionsofthesmallintestinesarecoveredwithtinyprojectionscalledvilli.

Villicontainverytinybloodvessels.Nutrientsareabsorbedintothebloodthroughthesetinyvessels.Therearemillionsofvilli,so,altogether,thereisaverylargeareaforabsorptiontotakeplace.Infact,villimaketheinnersurfaceareaofthesmallintestine1,000timeslargerthanitwouldbewithoutthem.Theentireinnersurfaceareaofthesmallintestineisaboutasbigasabasketballcourt!Thisiswhatthevilliliningtheintestinelookslikewhenmagnified.Eachoneisactuallyonlyabout1millimeterlong.Villiarejustbarelyvisiblewiththeunaidedeye.

Thesmallintestineismuchlongerthanthelargeintestine.Sowhyisitcalled“small”?Ifyoucomparesmallandlargeintestines(Figureabove),youwillseethesmallintestineissmallerinwidththanthelargeintestine. Large Intestine Thelargeintestineisawidetubethatconnectsthesmallintestinewiththeanus.Inadults,itisaboutfivefeetlong.Wasteentersthelargeintestinefromthesmallintestineinaliquidstate.Asthewastemovesthroughthelargeintestine,excesswaterisabsorbedfromit.Aftertheexcesswaterisabsorbed,theremainingsolidwasteiscalledfeces.Circularmusclescontroltheanus.Theyrelaxtoletthefecespassoutofthebodythroughtheanus.Afterfecespassoutofthebody,theyarecalledstool.Releasingthestoolfromthebodyisreferredtoasabowelmovement. Summary Themainorgansofthedigestivesystemarethemouth,esophagus,stomach,smallintestine,andlargeintestine.Theliver,gallbladder,andpancreascontributechemicalsthataidindigestion. Review

1. Listfiveorgansofthedigestivesystem.

2. Describeperistalsis,andexplainwhyitisnecessaryfordigestion.

3. Describethestomachanditsfunction.

4. Inwhichorganofthedigestivesystemdoesabsorptionofnutrientstakeplace?