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1、CHAPTER50SMALLINTESTINEShaunMcKenzieandB.MarkEversandproximaltwothirdsofthetransversecolon.Thejunctureembryologyofthecranialandcaudallimbsiswherethevitellineductjoinsanatomytotheyolksac.Thisductstructurenormallybecomesobliteratedphysiologybeforebirth;however,itcanpersistasaM
2、eckel’sdiverticulummotilityinapproximately2%ofthepopulation.Thismidgutherniationendocrinefunctionpersistsuntilabout10weeksoffetalgestation,whentheintes-immunefunctiontinereturnstotheabdominalcavity.Aftercompletinga270-obstructiondegreerotationfromitsinitialstartingpoint,thep
3、roximalinflammatorydiseasesjejunumreenterstheabdomenandoccupiestheleftsideoftheneoplasmsabdomen,withsubsequentloopslyingmoretotheright.Thececumenterslastandislocatedtemporarilyintherightupperdiverticulardiseasequadrant;however,withtime,itdescendstoitsnormalpositionmiscellane
4、ousproblemsintherightlowerquadrant.Congenitalanomaliesofgutmal-rotationandfixationcanoccurduringthisprocess.Theprimitivesmallbowelislinedbyasheetofcuboidalcellsuntilabouttheninthweekofgestation,whenvillibeginThesmallintestineisamarvelofcomplexityandefficiency.Thetoforminthep
5、roximalintestineandthenproceedinacaudalprimaryroleofthesmallintestineisthedigestionandabsorp-fashionuntiltheentiresmallbowel,andeventhecolon,forationofdietarycomponentsaftertheyleavethestomach.Thisperiodoftime,arelinedbythesefinger-likeprojections.Cryptprocessdependsonamulti
6、tudeofstructural,physiologic,endo-formationbeginsinthe10thto12thweeksofgestation.Thecrine,andchemicalfactors.Exocrinesecretionsfromthelivercryptlayerofthesmallbowelisthesiteofcontinualcellrenewalandpancreasenablecompletedigestionofthefoodstuffs.Theandproliferation.Asthecells
7、ascendthecrypt-villousaxis,pro-enlargedsurfaceareaofthesmallintestinalmucosathenabsorbsliferationceases,andcellsdifferentiateintooneofthefourmainthesenutrients.Inadditiontoitsroleindigestionandabsorp-celltypes:absorptiveenterocytes,whichcomposeabout95%oftion,thesmallbowelist
8、helargestendocrineorganinthebodytheintestinalcellpopulation;gobletcells;Pan
