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1、LymphaticandImmuneSystemsIntroductionLymphisaclear,wateryfluidthatsurroundsbodycellsandflowsinasystemoflymphvesselsthatextendsthroughoutthebody.Lymphfluidisrichintwotypesofwhitebloodcells:Lymphocytesandmonocytes.Theliquidpartoflymphissimilartobloodplasmainthatitcontainswater,sa
2、lts,sugarandwastesofmetabolismsuchasureaandcreatinine,butlessprotein.IntroductionLymphactuallyoriginatesfromtheblood.Itisthefluidthatfiltersoutoftinybloodvesselsintothespacesbetweencells.Thisfluidthatsurroundsbodycellsiscalledinterstitialfluid.Interstitialfluidpassescontinuousl
3、yintospecializedthin-walledvesselscalledlymphcapillaries,whicharefoundcoursingthroughtissuespaces.Thefluidinthelymphcapillaries,nowcalledlymphinsteadofinterstitialfluid,passesthroughlargerlymphaticvesselsandthroughdepositsoflymphtissues(lymphnodes),finallytoreachlargelymphvesse
4、lsintheupperchest.Lymphenterstheselargelymphaticvessels,whichthenemptyintothebloodstream.AnatomyLymphcapillaries[1]beginatthespacesaroundcellsthroughoutthebody.Likebloodcapillaries,theyarethin-walledtubes.Lymphcapillariescarrylymphfromthetissuespacestolargelymphvessels[2].Lymph
5、vesselshavethickerwallsthanthoseoflymphcapillariesand,likeveins,containvalvessothatlymphflowsinonlyonedirection,towardthethoraciccavity.Collectionsofstationarylymphtissue,calledlymphnodes[3],arelocatedalongthepathofthelymphvessels,.Thesemassesoflymphcellsvesselsaresurroundedbya
6、fibrous,connectivetissuecapsuleLymphnodesnotonlyproducelymphocytesbutalsofilterlymphandtrapsubstancefrominflammatoryandcancerouslesions.Specialcells,calledmacrophages,locatedinlymphnodes(aswellasinthespleen,liver,lungs,brain,andspinalcord),phagocytoseforeignsubstances.Whenbacte
7、riaarepresentinlymphnodesthatdrainaparticularareaofthebody,thenodesbecomeswollenwithcollectionsofcellsandtheirengulfeddebrisandbecometender.Lymphnodesalsofightdiseasewhenspecializedlymphocytes(B-celllymphocytes),presentinthenodes,produceantibodies.Otherlymphocytes(T-celllymphoc
8、ytes)attackbacteriaandforeignorcancerouscells,pokingho
