营养和消化 大学生物 Nutrition and Digestion

Chapter21,NutritionandDigestion,0,0,Introduction,Allanimalsmusteattoprovideenergyandthebuildingblocksusedtoassemble(組合)newmolecules.Animalsalsoneedessentialvitaminsandminerals.,0,Introduction,Themodernhumandietindevelopedcountriesallowsaccesstorelativelycheapandavailablecalorie-densefoods.Thisdiet,combinedwithsedentary(坐)jobsandinactivelifestyles,hasledtoanobesitycrisisintheUnitedStatesleadingto68%ofpeoplecategorizedasoverweightand100million(十億)peoplecategorizedasobese.Thus,themoderndietappearstobecontributingtoshorter,lesshealthylives.,Chapter21:BigIdeas,Nutrition,ObtainingandProcessingFood,TheHumanDigestiveSystem,0,OBTAININGANDPROCESSINGFOOD,0,21.1Animalsobtainandingesttheirfoodinavarietyofways,Mostanimalshaveoneofthreekindsofdiets.Herbivores(草食)eatplantsandincludecattle(家牛),snails,andseaurchins(海膽).Carnivores(肉食)eatmeatandincludelions,hawks,andspiders.Omnivores(雜食)eatplantsandotheranimalsandincludehumans,roaches(蟑螂),raccoons(浣熊),andcrows(烏鴉).,0,Animalsobtainandingesttheirfoodindifferentways.Suspensionfeeders(懸浮物攝食者)sift(過濾)smallorganismsorfoodparticlesfromwater.Substratefeeders(基質攝食者)liveinorontheirfoodsourceandeattheirwaythroughit.Fluidfeeders(流體攝食者)sucknutrient-richfluidsfromalivinghost.Bulkfeeders(大塊攝食者)ingestlargepiecesoffood.,21.1Animalsobtainandingesttheirfoodinavarietyofways,管蠕蟲,Caterpillar,Feces,蒼鷺,0,21.2Overview:Foodprocessingoccursinfourstages,Foodisprocessedinfourstages.Ingestion(攝食)istheactofeating.Digestion(消化)isthebreakingdownoffoodintomoleculessmallenoughforthebodytoabsorb.Absorption(吸收)isthetake-upoftheproductsofdigestion,usuallybythecellslining(內襯)thedigestivetract.Elimination(排除)istheremovalofundigestedmaterialsoutofthedigestivetract.,Mechanicaldigestion,Piecesoffood,Smallmolecules,Chemicaldigestion(hydrolysis),Nutrientmoleculesenterbodycells,Undigestedmaterial,Ingestion,Digestion,Absorption,Elimination,FoodMolecules,Components,Protein,Protein-digestingenzymes,Carbohydrate-digestingenzymes,Nucleic-acid-digestingenzymes,Fat-digestingenzymes,Aminoacids,Polysaccharide,Disaccharide,Monosaccharides,Nucleicacid,Nucleotides,Fat,Glycerol,Fattyacids,(核苷酸),0,21.3Digestionoccursinspecializedcompartments,Sponges(海綿)digestfoodinvacuoles(液泡).Mostanimalsdigestfoodincompartments(室).Cnidarians(腔腸動物)andflatworms(扁蟲)haveagastrovascularcavity(消化循環腔)withasingleopening,themouth.Foodentersthemouth.Enzymesbreakdownthefood.Foodparticlesmoveintocellsliningthecompartment.Undigestedmaterialsareexpelledbackoutthemouth.,0,Mostanimalshaveanalimentarycanal(消化道)withamouth,ananus,andspecializedregionsassociatedwithone-wayflowoffood.,21.3Digestionoccursinspecializedcompartments,0,Thenormalone-wayflowmovesfoodintothepharynx(咽)orthroat,downtheesophagus(食道)toacrop(嗉囊)wherefoodissoftenedandstored,gizzard(砂囊),wherefoodisground(磨碎)andstored,and/orstomach(胃)wherefoodisgroundandstored,totheintestines,wherechemicaldigestionandnutrientabsorptionoccur,andfinallyundigestedmaterialsareexpelledthroughtheanus(肛門).,21.3Digestionoccursinspecializedcompartments,Tentacles,Mouth,Food(awaterflea),Gastrovascularcavity,Digestiveenzymesbeingreleasedfromaglandcell,Fooddigestedtosmallparticles,Afoodparticlebeingengulfed,Afoodparticledigestedinafoodvacuole,hydra(水螅),(吞入),Earthworm,Mouth,Pharynx,Esophagus,Crop,Gizzard,Intestine,Anus,Grasshopper,Esophagus,Esophagus,Bird,Mouth,Mouth,Crop,Crop,Gizzard,Stomach,Intestine,Anus,Anus,Midgut,Hindgut,Gastricpouches,嗉囊,砂囊,後腸,中腸,胃囊,咽,0,THEHUMANDIGESTIVESYSTEM,0,21.4Thehumandigestivesystemconsistsofanalimentarycanalandaccessoryglands,Inhumans,foodisingestedandchewedinthemouthororalcavity,pushedbythetongueintothepharynx,movedalongbyalternatingwavesofcontractionandrelaxationbysmoothmuscleinthewallsofthecanalinaprocesscalledperistalsis(蠕動),andmovedinandoutofthestomachbysphincters(括約肌).,0,21.4Thehumandigestivesystemconsistsofanalimentarycanalandaccessoryglands,Thefinalstepsofdigestionandnutrientabsorptioninhumansoccurinthesmallintestine.Undigestedmaterialsmovethroughthelargeintestine,fecesarestoredintherectum(直腸),andthenexpelledouttheanus.,Key,Alimentarycanal,Accessorydigestiveglands,Rectum,Anus,Smallintestine,Largeintestine,Stomach,Esophagus,Oralcavity,Aschematicdiagramofthehumandigestivesystem,Salivaryglands,Gall-bladder,Liver,Pancreas,膽囊,Esophagus,Pharynx,Esophagus,Sphincters,Stomach,Smallintestine,Nasalcavity,Oralcavity(mouth),Tongue,Smallintestine,Largeintestine,Rectum,Anus,Salivaryglands,Gall-bladder,Liver,Pancreas,0,21.5Digestionbeginsintheoralcavity,Mechanicaldigestionandchemicaldigestionbegininthemouth.Chewingcuts,smashes,andgrindsfood,makingiteasiertoswallow.Thetonguetastes,shapesthefoodintoaballcalledabolus(食團),andmovesittowardthepharynx.,0,21.5Digestionbeginsintheoralcavity,Salivaryglands(唾液腺)releaseaslipperyglycoprotein(糖蛋白)thatmoistens(濡濕)andlubricates(潤滑)foodforeasierswallowing,buffers(緩衝)thatneutralizeacids,salivaryenzymeamylase(澱粉酶)thatbeginsthehydrolysisofstarch,andantibacterialagentsthatkillsomebacteriaingestedwithfood.,Incisors,Canine,Premolars,Molars,“Wisdom”tooth,Tongue,Salivaryglands,Openingofasalivaryglandduct,門牙,犬齒,前臼齒,臼齒,智齒,0,21.6Afterswallowing,peristalsismovesfoodthroughtheesophagustothestomach,Airmovesfromthepharynx,intothelarynx,pastthevocalcordsinthevoicebox,intothetrachea,andintothelungs.,0,21.6Afterswallowing,peristalsismovesfoodthroughtheesophagustothestomach,Swallowedfoodanddrinkmovefromthepharynx,intotheesophagus,andintothestomach.Duringswallowing,thetipofthelarynx(喉)movesupward,preventingthefoodfromenteringthetrachea.,Swallowingreflex(sphincterrelaxed),Epiglottisdown,Larynxup,會厭,Swallowingcompleted(sphinctercontracted),Epiglottisup,Larynxdown,Esophagealsphincter(contracted),Bolusoffood,Musclescontract,squeezingthebolusthroughtheesophagus.,Musclesrelax,allowingthepassagewaytoopen.,Bolusoffood,Stomach,0,21.7CONNECTION:TheHeimlichmaneuvercansavelives,TheHeimlichmaneuver(哈姆立克氏急救法)involvesaforcefulelevationofthediaphragm(橫膈膜),pushesairintothetrachea,andcandislodge(移動)foodfromthepharynxortracheaduringchoking(窒息).Braindamagewilloccurwithinminutesifnoairwayisopen.,0,21.8Thestomachstoresfoodandbreaksitdownwithacidandenzymes,Thestomachcanstretchandstoreupto2litersoffoodanddrink.Somechemicaldigestionoccursinthestomach.Thestomachsecretesgastricjuice(胃液),madeupofMucus(粘液)aprotein-digestingenzyme,andstrongacidwithapHofabout2thatkillsingestedbacteria,breaksapartcellsinfood,anddenaturesproteins.,0,21.8Thestomachstoresfoodandbreaksitdownwithacidandenzymes,Pepsinogen(胃蛋白酶原)andHClproduceactivepepsin(胃蛋白酶).Pepsinogen,H+,andClaresecretedintothelumen(內腔)ofthestomach.HClconvertssomepepsinogentopepsin.Pepsinhelpsactivatemorepepsinogen,startingachainreaction.Pepsinbeginsthechemicaldigestionofproteins.,0,Whatpreventsthegastricjuicesfromdigestingthewallsofthestomach?Thesecretionofpepsinintheinactiveformofpepsinogenhelpsprotectthecellsofthegastricglands.MucushelpsprotectthestomachliningagainstHClandpepsin.Newcellslining(內層)thestomachareproducedabouteverythreedaystothosethathavebeendamaged.,21.8Thestomachstoresfoodandbreaksitdownwithacidandenzymes,Esophagus,Sphincter,Lumen(cavity)ofstomach,Sphincter,Stomach,Smallintestine,Gastrin,Interiorsurfaceofthestomach,Releaseofgastricjuice(mucus,HCl,andpepsinogen),Pits,Epithelium,Mucouscells,Chiefcells,Parietalcells,Gastricgland,Pepsinogen,Pepsin(activeenzyme),HCl,Cl,H,胃泌素,主細胞,胃壁細胞,坑,0,21.9CONNECTION:Digestiveailmentsincludeacidrefluxandgastriculcers,Acidrefluxofchyme(食糜)inthestomachbackintotheesophaguscausesthefeelingofheartburn.Gastroesophagealrefluxdisease(GERD)(胃食道逆流)resultsfromfrequentandsevereacidrefluxthatharmstheliningoftheesophagus.Opensoresintheliningofthestomach,calledulcers,mayform.Bacterialinfections(Helicobacterpylori)(胃幽門螺旋桿菌)inthestomachandduodenum(十二指腸)canproduceulcers.,Bacteria,Mucouslayerofstomach,0,21.10Thesmallintestineisthemajororganofchemicaldigestionandnutrientabsorption,Thesmallintestineisnamedforitssmallerdiameter,about6meterslong,thesiteofmuchchemicaldigestion,andwheremostnutrientsareabsorbed.,0,21.10Thesmallintestineisthemajororganofchemicaldigestionandnutrientabsorption,Thefirst25cmofthesmallintestineistheduodenum(十二指腸),wherechymesquirted(噴出)fromthestomachmixeswithdigestivejuicesfromthepancreas,liver,gallbladder,andglandcellsintheintestinalwall.Thepancreas(胰臟)producespancreaticjuicecontainingamixtureofdigestiveenzymesandanalkaline(鹼性)solutionrichinbicarbonate(碳酸氫根).Theliverproducesbile,whichisstoredinthegallbladderuntilitisneeded.Bilebreaksupfatsintosmalldropletsthataremoresusceptibletoattackbydigestiveenzymes.Theintestinalwallproducesdigestiveenzymes.,Liver,Gall-bladder,Bile,Intestinalenzymes,Duodenumofsmallintestine,Chyme,Stomach,Pancreas,Pancreaticjuice,麥芽糖,澱粉酶,Trypsin:胰蛋白酵素Chymotrypsin:胰凝乳蛋白酶,0,Thesurfaceareaforabsorptioninthesmallintestineisgreatlyincreasedbyfoldsoftheintestinallining,fingerlikeprojectionscalledvilli(絨毛),andtinyprojectionsofthesurfaceofintestinalcellscalledmicrovilli(微絨毛).,21.10Thesmallintestineisthemajororganofchemicaldigestionandnutrientabsorption,Veincarryingbloodtotheliver,Musclelayers,Largecircularfolds,Villi,Intestinalwall,Lumen,Nutrientabsorption,Villi,Lymphvessel,Bloodcapillaries,Epithelialcells,Lumenofintestine,Microvilli,Nutrientabsorption,Fats,Blood,Lymph,Epithelialcellsofavillus,Aminoacidsandsugars,Fattyacidsandglycerol,0,Nutrientspassintoepithelialcellsbydiffusionandagainstconcentrationgradients.Fattyacidsandglycerolarerecombinedintofats,coatedwithproteins,andtransportedintolymphvessels.,21.10Thesmallintestineisthemajororganofchemicaldigestionandnutrientabsorption,0,Otherabsorbednutrientssuchasaminoacidsandsugarspassoutoftheintestinalepithelium,acrossthethinwallsofthecapillariesintoblood,andfinallytotheliver.,21.10Thesmallintestineisthemajororganofchemicaldigestionandnutrientabsorption,Villi,Lymphvessel,Bloodcapillaries,Epithelialcells,Lumenofintestine,Microvilli,Nutrientabsorption,Fats,Blood,Lymph,Epithelialcellsofavillus,Aminoacidsandsugars,Fattyacidsandglycerol,0,21.11Oneoftheliversmanyfunctionsisprocessingnutrient-ladenbloodfromtheintestines,Bloodfromthedigestivetractdrainsintothehepaticportalvein(肝門靜脈)totheliver.,0,21.11Oneoftheliversmanyfunctionsisprocessingnutrient-ladenbloodfromtheintestines,Theliverperformsmanyfunctions.Theliverconvertsglucoseinbloodtoglycogen(肝醣),storesglycogenandreleasessugarsbackintothebloodasneeded,synthesizesmanyproteinsincludingblood-clottingproteinsandlipoproteinsthattransportfatsandcholesteroltobodycells,modifiessubstancesabsorbedinthedigestivetractintolesstoxicforms,andproducesbile.,Liver,Intestines,Heart,Hepaticportalvein,0,21.12Thelargeintestinereclaimswaterandcompactsthefeces,Thelargeintestine,orcolon,isabout1.5mlongand5cmindiameter,hasapouchcalledthececum(盲腸)nearitsjunctionwiththesmallintestine,whichbearsasmallfingerlikeextension,theappendix(闌尾),containslargepopulationsofE.coli,whichproduceimportantvitamins,absorbsthesevitaminsandwaterintothebloodstream,andhelpsformfirmfeces,whicharestoredintherectum(直腸)untilelimination.,0,21.12Thelargeintestinereclaimswaterandcompactsthefeces,Diarrhea(腹瀉)occurswhentoolittlewaterisreclaimedfromthecontentsofthelargeintestine.Constipation(便秘)occurswhentoomuchwaterisreclaimed.,Cecum,Appendix,Endofsmallintestine,Largeintestine(colon),Unabsorbedfoodmaterial,Smallintestine,Rectum,Anus,0,21.13EVOLUTIONCONNECTION:Evolutionaryadaptationsofvertebratedigestivesystemsrelatetodiet,Thelengthofthedigestivetractoftencorrelateswithdiet.Ingeneral,thealimentarycanalsrelativetotheirbodysizearelongerinherbivoresandomnivoresandshorterincarnivores.,Stomach,Smallintestine,Cecum,Colon(largeintestine),Carnivore,Herbivore,0,Manyherbivoreshavespecializationsofthegutthatpromotethegrowthofcellulose-digestingbacteriaandprotists(原生生物)becausetheseanimalslacktheenzymesneededtodigestcelluloseinplants.Thesemutualisticorganismsmaybehousedinthececum,inacoyoteorkoala,thelargeintestineandthececuminrabbitsandsomerodents,orthestomachofruminants(反芻動物)suchascattle,sheep,anddeer.,21.13EVOLUTIONCONNECTION:Evolutionaryadaptationsofvertebratedigestivesystemsrelatetodiet,0,NUTRITION,0,21.14Overview:Ananimalsdietmustsatisfythreeneeds,Allanimalshavethesamebasicnutritionalneeds.Animalsmustobtainfueltopowerallbodyactivities,organicmoleculestobuildtheanimalsownmolecules,andessentialnutrients,orsubstancestheanimalcannotmakeforitself.,0,21.15Chemicalenergypowersthebody,Cellularrespirationproducesthebodysenergycurrency,ATP,byoxidizingorganicmoleculesdigestedfromfoodandusuallyusingcarbohydratesorfatsasfuel.Agramoffathasmorethantwiceasmanycaloriesasagramofcarbohydrateorprotein.,0,21.15Chemicalenergypowersthebody,Theenergycontentoffoodismeasuredinkilocalories(1kcal=1,000calories).DietarycaloriesareactuallykilocaloriesandarewrittenasCalories.,0,Therateofenergyconsumptionbyananimaliscalleditsmetabolicrate(代謝率),thesumofalltheenergy-requiringbiochemicalreactionsoveragivenintervaloftime.Thebasalmetabolicrate(BMR)(基礎代謝率)istheenergyarestinganimalrequireseachday.ThemetabolicrateistheBMRplustheenergyneededforphysicalactivity.Excessenergyisstoredasglycogenorfat.,21.15Chemicalenergypowersthebody,慢跑,0,21.16Ananimalsdietmustsupplyessentialnutrients,Essentialnutrientscannotbemadefromanyrawmaterial.Therearefourclassesofessentialnutrients.Essentialfattyacids,suchaslinoleicacid(亞油酸),areusedtomakephospholipids(磷脂質)ofcellmembranesandfoundinseeds,grains,andvegetables.Essentialaminoacidsareusedtomakeproteinsandfoundinmeats,eggs,andmilk.,0,Vitaminsareorganicnutrients.Mineralsaresimpleinorganicnutrients.Malnutrition(營養不良)isachronicdeficiencyincaloriesoroneormoreessentialnutrients.Themostcommontypeofhumanmalnutritionisproteindeficiency.Under-nutrition(營養不足)occurswhendietsdonotsupplysufficientchemicalenergyorapersonsuffersfromanorexianervosa(厭食症)orbulemia(暴食症).,21.16Ananimalsdietmustsupplyessentialnutrients,Essentialaminoacids,Corn,Beansandotherlegumes,Lysine,Tryptophan,Isoleucine,Leucine,Phenylalanine,Threonine,(Histidine),Valine,Methionine,0,21.17Ahealthyhumandietincludes13vitaminsandmanyessentialminerals,Essentialvitaminsandmineralsarerequiredinminuteamounts(微量)andabsolutelyessentialtogoodhealth.Vitaminsareorganicnutrientsthatmaybewatersoluble,suchasvitaminsBandC,orfatsoluble,suchasvitaminsA,D,E,andK.,0,Minerals(礦物質)aresimpleinorganicnutrients.Calciumandphosphorusarerequiredinlargeramounts.Ironisneededtomakehemoglobin(血紅素).Iodineisrequiredtomakethyroidhormones.Mostpeopleingestmoresaltthantheyneed.,21.17Ahealthyhumandietincludes13vitaminsandmanyessentialminerals,0,TheRecommendedDietaryAllowances(RDAs)(營養攝取建議表)aretheminimumamountsofnutrientsthatareneededeachdayanddeterminedbyanationalscientificpanel.Overdosesofvitaminscanbeharmful.Ingeneral,excesswater-solublevitaminswillbeeliminatedinurine.However,excessfat-solublevitaminscanaccumulatetotoxiclevelsinbodyfat.,21.17Ahealthyhumandietincludes13vitaminsandmanyessentialminerals,0,21.18SCIENTIFICDISCOVERY:Scientistsuseobservationsandexperimentstodeterminenutritionalneeds,Manyinsightsintohumannutritionhavecomefromepidemiology(流行病學),thestudyofhumanhealthanddiseaseswithinpopulations.TheessentialneedforvitaminCwasrevealedbythehighincidenceofscurvy(壞血病)insailorsonlongseavoyages.Theneedforfolicacid(葉酸)topreventneuraltubedefectsinnewbornswasrevealedbystudiesofpregnantwomenoflowsocioeconomicstatus.Since1998,folicacidhasbeenaddedtofoodssuchasbreadandcerealssoldintheUnitedStates.,0,21.19CONNECTION:Foodlabelsprovidenutritionalinformation,Foodlabelsindicateservingsize,caloriesperserving,amountsofselectednutrientsperservingandasapercentageofdailyvalue,andrecommendationsfordailylimitsofselectednutrients.,Ingredients:wholewheatflour,water,highfructosecornsyrup,wheatgluten,soybeanorcanolaoil,molasses,yeast,salt,culturedwhey,vinegar,soyflour,calciumsulfate(sourceofcalcium).,0,21.20EVOLUTIONCONNECTION:Thehumanhealthproblemofobesitymayreflectourevolutionarypast,Overnourishmentistheconsumptionofmorefoodenergythanisneededfornormalmetabolism.Obesityistheexcessiveaccumulationoffat.TheWorldHealthOrganizationrecognizesobesityasamajorglobalhealthproblem.IntheUnitedStates,thepercentageofobesepeoplehasdoubledtomorethan30%inthepasttwodecades,andanother35%areoverweight.,0,Weightproblemsoftenbeginatayoungage.15%ofchildrenandadolescents(青少年)intheUnitedStatesareobese.Another17%areoverweight.Obesityleadstotype2diabetes,cancerofthecolonandbreasts,andcardiovasculardisease.,21.20EVOLUTIONCONNECTION:Thehumanhealthproblemofobesitymayreflectourevolutionarypast,0,Obesityisestimatedtobeafactorin300,000deathsperyearintheUnitedStates.A15-yearstudypublishedin2010indicatesthatobesitynowsurpassessmokinginitscontributiontodiseaseandtheshorteningofhealthylifespans.,21.20EVOLUTIONCONNECTION:Thehumanhealthproblemofobesitymayreflectourevolutionarypast,0,Thecomplexityofweightcontrolinhumansisevidentfromstudiesofthehormoneleptin.Leptin(瘦素)isproducedbyadipose(fat)cellsandsuppressesappetite.Obesechildrenwhohaveaninheritedmutantformoftheleptingeneloseweightafterleptintreatments.However,highlevelsinotherwisehealthypeopledonotsuppressappetite(食慾).,21.20EVOLUTIONCONNECTION:Thehumanhealthproblemofobesitymayreflectourevolutionarypast,0,21.21CONNECTION:Whatarethehealthrisksandbenefitsofweightlossplans?,Whyaresomanypeopleoverweight?Isitlackofexercise,theamountoffood,thequalityoffood,oracombinationoftheabove?TheU.S.marketforweightlossproductsandserviceshasgonefromabout$60millionayearin1999tomorethan$48billionayeartoday.,0,21.21CONNECTION:Whatarethehealthrisksandbenefitsofweightlossplans?,Weightlossdietsmayhelpindividualsloseweightbuthavehealthrisksleadingtomalnourishment.Someseverelyobeseindividualsmaybecandidatesforweightlosssurgery.,0,21.21CONNECTION:Whatarethehealthrisksandbenefitsofweightlossplans?,Scientificstudiesofweightlossdietsindicatethatthebestwaytoloseweightandkeepitoffistoincreaseexerciseandeatabalanceddietwithadequateamountsofallessentialnutrients.,Weight(pounds),100,120,140