动物生理学6.消化与吸收(三)

胃底和胃体的上部主要用于接受和容纳作物，胃体中下部和胃窦的功能主要是混合、磨碎食物形成食糜，并向小肠输送食物（胃排空）。6.3.2GastricMotilityGastricpumpPhasiccontractionsBFundusCorpusAntrumPylorusA[pai’lɔ:rəs]6.3.2.1Formsandregulationofgastricmotility•Receptiverelaxation•Toniccontraction•Gastricperistalsis食物入胃5min后开始，从胃中部开始，每分3次,1分钟到幽门。意义：使食物与胃液充分混合，磨碎食物，推动食物向十二指肠移行。胃蠕动的控制基本电节律，迷走神经、胃泌素和胃动素加强之，促胰液素和抑胃肽抑制之。6.3.2.2GastricemptyinganditscontrolGastricemptying胃的排空食物由stomach排入duodenum的过程Theprocessbywhichthechymeisexpelledfromthestomachintotheduodenumiscalledgastricemptying.排空时间non-digestiblespheres[pai’lɔ:rik]胃内因素促进排空扩张刺激（排空速率与胃内食物量的平方根成正比)；蛋白质水解产物刺激胃窦释放胃泌素。ControlofGastricemptyingControlofgastricemptying十二指肠因素抑制排空•肠胃反射•十二指肠产生的激素，•酸、脂肪、过量的食糜、渗透压Inhibitoryeffectsinduodenumandjejunum–throughreflexesandhormonesInhibitoryreflexes–direct–myentericplexusindirect–viaextrinsicnervesNeuralreflexesstimulatedby:Distension,irritation,acidity,highosmolarity,protein/fatFatsandacidsalsostimulatereleaseofhumoralfactorswhichreducegastricemptyingCholecystokinin(CCK),stimulatedbyfatsSecretin,stimulatedbyacidsEnterogastricReflexregulatestherateatwhichchymeleavesthestomachThefeedbackregulationofgastricemptyingisperformedbyentero-gastricreflexesandreleaseofintestinalhormonesFigure14Figure14Itcausesenhancedrelaxationofthegastricreservoir,inhibitionoftheantralpump,andreducedopeningofthepyloricsphincter.VagalcenterInhibitoryvagalfibersNO,VIPetal.CCKAchEnhancedrelaxationandstorageStimulatingcholinergicvagalfibersNutrientsLongchainfattyacidsAminoacidsDipeptidsGlucoseOsmolalityHydrochloricacidReducedopeningofpyloricsphincterReducedcontractionBackflow++_Ach6.3.2.3gastricmotilityininterdigestivephase•在消化间期即空腹状态下，小肠运动的主要形式是周期性的移行性复合运动(migratingmotorcomplex,MMC)。MMC起源于胃的中部，向大肠方向缓慢移行。•小肠MMC是一种周期性的时相性收缩，根据小肠静止和运动空替出现的周期性变化．整个MMC周期可分为4个时相；I相为静止期．几乎没有收缩活动．持续约40～50min；Ⅱ相为间断的不规则收缩期，持续约40min；Ⅲ相为强力收缩期，以最大频率规律地收缩．十二指肠、空肠约为l2次/min，回肠10次/min，持续约l0min；Ⅳ相为过度期,持续约5min。MMC周期平均约为90～120min。小肠MMC的生理学作用主要有：•①起胃肠“清道夫”的作用，在下改进餐前清除粘液、脱落的上皮细胞，排出未消化的食物残渣；•②防止胃肠淤滞及肠道细菌过度增长•③产生饥饿信号，促进摄食活动。6.4Digestioninsmallintestine小肠是消化t和吸收最重要的部位，pancreaticjuice,bile,小肠液富含消化酶，消化和吸收在经小肠后基本完成。