digestive system part 2

aboutabout 2525--cmcm--long long muscularmuscular tubetube

functionfunction: : forwardingforwarding swallowedswallowed foodfood fromfromthethe pharynxpharynx downdown intointo thethe stomachstomach

itsits lumen is lumen is starstar--shapedshaped, , duedue toto thethelongitudinallongitudinal reservereserve foldsfolds

thethe typicaltypical structurestructure ofof thethe alimentaryalimentary canalcanalappearsappears inin thisthis segmentsegment

epitheliumepithelium ((laminalamina epithelialisepithelialis mucosaemucosae):):stratifiedstratified, , nonkeratinizednonkeratinized squamoussquamousepitheliumepithelium atat itsits entireentire lengthlengthlaminalamina propriapropria mucosaemucosae comprisescomprises cardiaccardiacesophagealesophageal glandsglands ((glandulaeglandulae oesophageaeoesophageaecardiacaecardiacae) ) inin itsits beginingbegining andand terminalterminalportionsportions; ; thesethese glandsglands resembleresemble thethe cardiaccardiacglandsglands, hence , hence thethe namename

cardiaccardiac esophagealesophageal glandsglands produceproduce neutralneutral mucin, mucin, whichwhich protectsprotects thethe cellscells againstagainst thethe possiblepossible refluxrefluxofof gastricgastric juicejuiceinin thethe laminalamina propriapropria, , therethere areare scatteredscattered lymphaticlymphaticelementselements, , frequentlyfrequently inin thethe vicinityvicinity ofof thethe excretoryexcretoryductsductslaminalamina muscularismuscularis mucosaemucosae is is composedcomposed ofof mainlymainlylongitudinallongitudinal smoothsmooth musclemuscle cellscells

is is thrownthrown intointo longitodinallongitodinal foldsfolds, , justjust likelikemucousmucous membranemembranetherethere areare mixedmixed oror purelypurely mucousmucous smallsmallsalivarysalivary glandsglands, , whichwhich areare calledcalled esophagealesophagealglandsglands properproper ((glandulaeglandulae oesophageaeoesophageaepropriaepropriae))

inin thethe upperupper oneone--thirdthird, , striatedstriated musclemuscle cancan be be foundfound, , onlyonly

inin thethe middlemiddle approximatelyapproximately oneone--thirdthirdsegmentssegments, , thethe striatedstriated andand smoothsmooth musclesmusclesareare intermingledintermingled

inin thethe lowerlower oneone--thirdthird, , therethere areare smoothsmoothmusclemuscle cellscells, , onlyonly

tunicatunica adventitiaadventitia is is thethe outermostoutermost mainmain layerlayerofof thethe esophagusesophagus; ; thisthis layerlayer connectsconnects thethemajoritymajority ((cervicalcervical andand thoracicthoracic portionsportions) ) ofofthethe organorgan toto thethe surroundingsurrounding tissuetissue

thethe abdominalabdominal portionportion, , howeverhowever, is , is replacedreplacedbyby tunicatunica serosaserosa ((serousserous membranemembrane))

beanbean--shaped hollow muscular organ of the shaped hollow muscular organ of the gastrogastro--intestinal tract involved in the second intestinal tract involved in the second phase of digestionphase of digestionitit has has fourfour anatomicalanatomical partsparts: : cardiacardia, fundus, , fundus, bodybody andand pyloruspylorusitit has has threethree histologicalhistological distinctdistinct partsparts: (1) : (1) cardiacardia, (2) , (2) thethe fundus fundus andand thethe bodybody havehave thethesamesame histologicalhistological propertiesproperties, (3) , (3) pyloruspylorus

simplesimple columnarcolumnar epitheliumepithelium invaginatesinvaginatesintointo thethe laminalamina propriapropria, , therebythereby itit makesmakesgastricgastric pitspits ((foveolaefoveolae gastricaegastricae))thethe tubulartubular glandsglands ((cardiaccardiac --, , fundicfundic-- andandpyloricpyloric glandsglands) ) ofof stomachstomach emptyempty intointo thethebottombottom ofof thethe gastricgastric pitspitsthethe epithelialepithelial cellscells produceproduce thickthick, , neutralneutralmucinmucin, , whichwhich protectsprotects thethe cellscells themselvesthemselvesfromfrom highlyhighly acidicacidic gastricgastric juicejuice

looseloose connectiveconnective tissuetissue, , whichwhich maymay containcontainmanymany lymphocyteslymphocytesallall thethe gastricgastric glandsglands areare locatedlocated inin thisthis laminalaminainin thethe threethree histologicalhistological portionsportions ofof thethestomachstomach thethe glandsglands display display somewhatsomewhatdifferentdifferent morphologymorphology; ; theirtheir productsproducts areare alsoalsodifferentdifferent

a a laminalamina muscularismuscularis mucosaemucosaewellwell--developeddeveloped, , usuallyusually is is composedcomposed ofof twotwo sublayerssublayersofof smoothsmooth musclemuscle cellscells

looseloose coonectingcoonecting tissuetissue, , containingcontainingbloodblood vesselsvessels

lymphaticslymphatics

lymphocyteslymphocytes

solitarysolitary fatfat cellscells

macrophagesmacrophages

mastmast cellscells

containscontains smoothsmooth musclemuscle cellscellscomposedcomposed ofof sublayerssublayers::

outermostoutermost sublayersublayer:: discontinuousdiscontinuous; ; comprisecomprise mainlymainlylongitudinallylongitudinally orientedoriented smoothsmooth musclesmuscles cellscells, , whichwhich maymaybe be absentabsent fromfrom areasareas withinwithin thethe pyloricpyloric portionportionmiddlemiddle sublayersublayer: : circularlycircularly arrangedarranged smoothsmooth musclemuscle cellscells, , wellwell--developeddeveloped throughoutthroughout thethe stomachstomach; ; thethe middlemiddlesublayersublayer is is greatlygreatly enhancedenhanced inin thethe pyloricpyloric portionportion, , wherewhereitit isis calledcalled pyloricpyloric sphinctersphincter musclemuscleinnermostinnermost sublayersublayer: : obliqueoblique bundlesbundles ofof smoothsmooth musclemusclecellscells maymay occuroccur

The The stomachstomach is is anan intraperitonealintraperitoneal organorgan. . ItsItsoutermostoutermost mainmain layerlayer isis a a serousserous membranemembraneofof looseloose coonectivecoonective tissuetissue andand mesotheliummesotheliumtowardstowards thethe peritonealperitoneal cavitycavity..

locatedlocated inin thethe laminalamina propriapropria, , whichwhich arearedifferentdifferent inin thethe histologicalhistological portionsportions::

cardiaccardiac glandsglands

fundicfundic glandsglands

pyloricpyloric glandsglands

simplesimple oror branchedbranched glandsglands, , locatedlocated inin thethe cardiaccardiacportionportion

thethe secretorysecretory cellscells resembleresemble thethe surfacesurface mucousmucous cellscellsofof thethe gastricgastric pitspits

produceproduce mucinmucin

branchedbranched tubulartubular glandsglandsseveralseveral glandsglands openopen intointo oneone gastricgastric pitpithavehave segmentssegments

inin thethe upperupper segmentsegment (( neckneck ))neckneck mucousmucous cellscellsundifferentiatedundifferentiated stemstem cellscells

inin thethe middlemiddle andand lowerlower segmentssegments ((principalprincipalsegmentsegment))

H ClH Cl--producingproducing parietalparietal cellscellschiefchief cellscells, , whichwhich secretesecrete pepsinogenpepsinogenenteroendocrineenteroendocrine cellscells

inin thethe pyloricpyloric regionregion, , thethe gastricgastric pitspits arearedeeperdeeper thanthan inin thethe otherother onesonesthethe pyloricpyloric glandsglands areare branchedbranched tubulartubularglandsglands withwith curvedcurved endsendsthethe secretorysecretory cellscells stainstain lightlylightlytheythey produceproduce mucin mucin andand antibacterialantibacteriallysozymelysozymeenteroentero--endocrineendocrine cellscells areare alsoalso presentpresent