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Bio230-LymphaticSystemMajorFunctions:1.FluidBalance-collectsexcesswaterandproteinsfrominterstitialfluidandreturnsittothebloodstream.2.Fat(lipid)absorptionandtransportationtobloodstream-Speciallymphaticcapillaries(lacteals)receiveallabsorbedfat(chyle)fromthesmallintestineandtransportitthroughtheThoracicDucttothevenoussystem.3.Defendsthebodyagainstpathogens(diseasecausingagentssuchasbacteria,viruses,fungi,parasites,cancer)ComponentsoftheLymphaticSystem:1.Lymph2.Lymphaticvessels3.LymphaticTissue/Organs______________________________________________________________________________________________WhatisLYMPH?(FirstcomponentoftheLymphaticSystem)Asbloodflowsthroughsystemiccapillariesasmallamountoffluidisexuded(discharged)intotheinterstitialspace,mostofthefluidisreturnedtothecirculationbyveins,butabout3litersadayisleftandreturnedtothecirculationvialymphaticvessels.Thisfluidiscalledlymph…kindalikeplasma,mostlywater,someproteinsandlotsofWBC’s(mostlylymphocytesandsomemonocytes).LymphisLatinfor“clearwater”.Lymphflowsinonedirection…alwaysbacktotheheart._____________________________________________________________________________________________________________LymphaticVessels(SecondcomponentoftheLymphaticSystem)include:Lymphaticcapillaries,lymphaticcollectingvessels,lymphatictrunksandlymphaticducts.a.Lymphaticcapillaries-thesecapillariesarefoundalongsidemostbloodcapillariesinthebody(notfoundinCNS).Composedoflooselyattachedoverlappingsimplesquamousepithelialcells.Thustheyarequitepermeable(evenmoresothanbloodcapillaries).Fluidenterseasily,asdoproteins,WBC’s,pathogensandcancercells.RememberthespecializedlymphaticcapillariesmentionedabovecalledLACTEALS?LymphwithinlactealsiscalledCHYLE.b.Lymphaticcollectingvessels=receivelymphfromlymphaticcapillaries.Similartoveins(tunicssimilar),butcontainmorevalves.TheselymphaticcollectingvesselspassthroughLYMPHNODES,wherelymphiscleanedofpathogensandcancercells.c.Lymphatictrunks=formedbytheunionofthelargestlymphaticvessels.Thereare5.1.Jugulartrunks(paired)-locatedatthebaseofeachinternaljugularvein;draintheheadandneck.2.Subclaviantrunks(paired)-draintheupperlimbs,superficialthoracicwall,andmammaryglands.3.Bronchomediastinaltrunks(paired)-drainthoracicorgansandthedeepthoracicwall.4.Intestinaltrunk(unpaired)-drainstheintestines,stomach,pancreas,spleen,andliver.5.Lumbartrunks(paired)-drainthelowerlimbs,pelvicandabdominalwalls,pelvicorgans,gonads,kidneys,andadrenalglands.

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d.Lymphaticducts=formedbytheunionoflymphatictrunks.Therearetwolymphaticducts.TheRIGHTLYMPHATICDUCTandtheTHORACICDUCT.1.RIGHTLYMPHATICDUCT-Drainslymphfromtherightarm,rightsideoftheheadandneck,andrightthorax.Dumpsthelymphbackintothevenouscirculationatthejunctionoftherightsubclavianveinandrightinternaljugularvein.2.THORACICDUCT-Over¾’softhebody’slymphisdrainedintothethoracicduct.ThisductbeginsintheabdomenasasaccalledtheCISTERNACHYLIcontinuessuperiorlytodrainlymphfromthelegs,abdomen,leftarm,leftsideofthethorax,leftsidesofhead&neck.TheThoracicductdumpsthelymphbackintothevenouscirculationbetweentheleftsubclavianveinandtheleftinternaljugularvein.Besureyoucan“see”theRightLymphaticDuctandTheThoracicDuctandtheircomponents,AlltheLymphfromthelowerextremitiesandabdomendrainintotheCisternaChyli.Besureyoucanseethis,rememberTheThoracicDuctreceivesLymphfromtheCisternaChyli.

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Thisnextdiagramshowshowthelymphaticsystemfollowsthevenoussystembacktotheheart.BesureyoucanseewheretheRightLymphaticDuctandtheThoracicDuctdumptheirlymphbackintothevenouscirculation.

Remember…lymphaticvesselsaresimilartoveins.Bothneedvalvestokeeplymphmovingforward(andnotbackwards),need“action”oftheskeletalmusclestohelpmovelymphmovingforwardtowardstheheart.InabilitytomovelymphresultsinaexcessofISF(interstitialFluid)accumulation,i.e.EDEMA._______________________________________________________________________________________________________________ThethirdcomponentoftheLymphaticSystemis-LymphaticTissue/Organs.Theseinclude:TheSpleen,Lymphnodes,Thymus,Tonsils,andPeyer’sPatchesinthesmallintestines.SPLEEN_-Largestmassoflymphatictissueinbody.LocatedinLUQ,behindstomach.Functions:1.Tofilterbloodofpathogens2.DestroyoldRBC’s3.ProductionoflymphocytesThespleenhasareasof“WhitePulp”and“RedPulp”.Thewhitepulphasacentralarterysurroundedbymassesoflymphocytes.Itishereinthewhitepulpthebloodisfilteredforpathogens,whicharedestroyedastheyactivatetheimmuneresponse.Thewhitepulpprovides

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theimmunefunctionofthespleen.Theredpulpsurroundsthewhitepulp.Itisherewheremacrophagesphagocytizeoldwornout/defectiveRBC’s.LYMPHNODES-Clusteredalongtheroutesoflymphaticvesselsandfilterthelymphthatflowsthroughthem.Afferentlymphaticvesselsbringlymphintothelymphnodes.Thelymphasitflowsthroughthelymphnodeisscrutinizedbymacrophages(whichphagocitizeforeignparticlesandpathogens)andlymphocytes(whichwillproliferateandmountanimmuneresponse)ifpathogensaredetected.Thisiswhyyouhave“swollen”lymphnodessometimeswhenyouare“sick”.Efferentvesselsleaveatanindentationinthenodecalledthehilum.Typicallytherearemoreafferent(incoming)thanefferent(outgoing)vessels,whichcreatesabottleneckthatforcesthelymphtoflowslowly,thusgivinglymphocytesandmacrophagesmoretimetoperformtheirsurveillance.duties!BELOWISADIAGRAMOFATYPICALLYMPHNODE:

Therearehundredsoflymphnodesinthebody.Mostaredeep,butlargesuperficialclustersarelocatedinthecervical,axillaryandinguinalregions.Thesearethelymphnodesyourdoctorpalpates(touches)toevaluateyouforpossible“pathogen”intrusion.Axillarylymphnodespalpatedduringafemalesbreastexamaspartofabreastcancerscreen.Yourcervicallymphnodesareusuallyenlargedandtenderwhenyouhaveathroatinfection.Nowyouknowwhy!!!THYMUS-Location=superiormediastinum,justsuperficialtothegreatvesselsoftheheart(pulmonarytrunkandascendingaorta).Itisabi-lobedstructure.Function-immaturelymphocytes(whichareproducedintheredmarrowofbone),traveltotheThymuswhentheydevelopintoTlymphocytes.TheThymus(akaThymusGland)secreteshormonesinvolvedinTlymphocytematuration.Thethymusislargestwhenweareveryyoung.

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Duringadolescenceitbeginstoatrophy,Byage40ithasonlyabout2%ofitsoriginaltissue,anditisreplacewithfatty/fibroustissue.TheThymusisuniqueinthatitistheonlylymphoidorganthatdoesnotdirectlyfightpathogens.

TONSILS:Formaringoflymphatictissueattheentrancetothepharynx,toprotectthedigestiveandrespiratorysystems.TonsilsdonotfilterlymphbutproduceBlymphocytes.3maintonsils:palatine,pharyngeal,andlingual.(Highlighttheminthediagrambelow)1.Palatinetonsilsarepairedandlocatedoneithersideoftheposteriororalcavity.Theyarethelargestandmostofteninfected.“Tonsillitis”2.Lingualtonsilisacollectionoflymphoidtissueatthebaseofthetongue.3.Pharyngealtonsilisfoundintheposteriorwallofthenasopharynxandidreferredtoastheadenoidsifenlarged.

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Tonsilsareuniqueamonglymphoidorgansinthattheirsurfaceisoverlainbyepithelium.Theycontaindeepinvaginationsknownascrypts.Thestragedyistoinvitebacteriaintothecryptsanddestroythem.Thiswideexposuretobacteriaandvirusesresultsinthecreationofalotof“memory”immunecellsthatcanswiftlydealwithinvaderslaterinlife.PEYER’SPATCHES-massesoflymphoctesinthewalloftheileum(terminalpartofsmallintestines).Thesedestroyanybacteriatryingtoinvadethesmallintestinesfromthecolon.Peyer’sPatchesarepartofwhataretermedMucosaAssociatedLymphaticTissueakaMALT.Histologyofileumofsmallintestines(crosssection)LumenofileumIntestinalvillifacelumenThesedarkpurpleclumpsarethePeyer’sPatches.