EXCRETION IN ANNELIDA.pdf

By Abu Rehan

1. RAJEEV RANJAN
ASSISTANT PROFESSOR
DEPARTMENT OF ZOOLOGY
PATNA WOMEN’S COLLEGE
SEMESTER –II
ZOO CC203
UNIT-1

2. EXCRETION IN ANNELIDA
•Excretionistheprocessofremovalofmetabolicwasteproductsfromthebody.
•InAnnelidanitrogenouswasteproductsandcarbondioxideareformedduring
metabolismandareremovedfromthebodythroughnephridia.
Definitionofnephridium
Anexcretorytubulewhichopenstotheexteriorthroughthenephridioporeand
theinnerendofthetubuleisblind(associatedwithterminalcellsorsolenocytes)
intheprotonephridiumoropensinthecoelomthroughtheciliatedfunnelare
callednephrostomeinmetanephridium.

4. Structure of a typical nephridium
•Atypicalnephridiumconsistsofanephrostomeoraciliatedfunnelwhichhangs
intothecoelomandleadstothenephridialduct.
•Thenephridialductorbodyofthenephridiummaybelong,short,convolutedor
modifiedotherwise.
•Theductisciliatedinternally,situatedtransverselyandisaccompaniedbyblood
vessels.
•Thenephridialductopenstotheexteriorbyanopening,callednephridiopore.

5. AnnelidNephridia.(a)Protonephridium.Thebulbularendsofthisnephridiumcontainatuftofflagellathatdriveswastestothe
outsideofthebody.Inprimitiveannelids,agonoduct(coelomoduct)carriesreproductiveproductstotheoutsideofthebody.(b)
Metanephridium.Anopenciliatedfunnel(thenephrostome)driveswastestotheoutsideofthebody.(c)Inmodernannelids,the
gonoductandthenephridialtubulesundergovaryingdegreesoffusion.(d)Nephridiaofmodernannelidsarecloselyassociatedwith
capillarybedsforsecretion,andnephridialtubulesmayhaveanenlargedbladder

6. Excretion in Earthworm
•Excretoryorgansofearthwormis
nephridia.
•Inthebodyofearthwormthreekinds
ofnephridiaoccur:
(a)Septalnephridia
(b)Integumentarynephridiaand
(c)Pharyngealnephridia

7. Septal nephridia
•Septalnephridiaremainattachedtothetwofacesoftheseptum.
•Theyoccurfrom15thsegmentback-ward.Thatmeansinthefirstfourteensegments
theyareabsent.
•Eachseptumbears40-50nephridiainaverageinitsanteriorandasimilarnumberonits
posteriorface.
•Thusineachsegmentthereareabout80-100nephridia.
Structureofseptalnephridium
•Atypicalseptalnephridiumconsistsofamainbodyformedbyastraightlobeandalong
narrow,spirallytwistedloop,afunnellikenephrostomeconnectedtothemainbodyby
ashortneckandaterminalnephridialduct.
•Thenephrostomeorciliatedfunnelisaroundedstructure.Themouthofthefunnel
whichcommunicateswiththecoelomisprovidedwithalargeupperlipandasmall
lowerlip.Thelipsareciliatedandareprovidedwithseveralrowsofciliatedmarginal
cells.
•Anarrowciliatedtuberunsfromthefunnelintothebodyofthenephridium,calledneck
andtakesseveralturnsinsideit.

8. •Themainbodyofthenephridiumismadeupofamainlobeandaspirallytwistedloop.
•Theloopistwiceaslongasthemainlobeandconsistsofaproximallimbandadistallimb
twistedroundeachother.
•Thestraightlobeiscontinuedasthedistallimbofthetwistedloopandtheproximallimb
receivestheciliatedtubulefromthenephrostomeandalsoitgivesofftheterminalductwhich
opensatthenephridiopore.
•Thestraightlobebearsfourparalleltubules,theproximalanddistalonesbearthreetubuleseach
andintheapicalparttherearetwotubules.
•Terminalductsoftheseptalnephridiumopenintoaseptalexcretorycanalwhichrunsparallel
andinternaltocommissuralvessels.
•Thereareapairofseptalexcretorycanalsoneoneachsideoftheseptum.
•Thetwoseptalexcretorycanalsopenintoapairofsupra-intestinalexcretoryductswhichrunon
themid-dorsallinesidebysidefrom15thsegmenttotheposteriorend.
•Thesupra-intestinalexcretoryductsopenintothelumenoftheintestinebysingleandsmall
ductsatthelevelofeachinter-segmentalseptum.

9. Different structural views of septal nephridiain Pheretima(Earthworm)

10. Integumentary nephridia
•Theyaresmallerinsizethantheseptal
nephridia.
•These'V'-shapedstructuresoccuronthe
innersurfaceoftheintegumentinall
segmentsexceptingthefirsttwo.
•Theynumber200-250ineachsegment
butinthe14th,15thand16thsegments
thenumberofnephridiaismuchmore.
•Structurallytheyresembleseptal
nephridiabutlackthenephrostome.
•Theyopenindependentlytotheoutside
bynephridioporesontheoutersurfaceof
the-bodywall.
Integumentary nephridia

11. Pharyngeal nephridia
•Theyareaslargeastheseptalnephridiaandoccurintheformofthreepairsofbunchesortuftsinthe
4th,5thand6thsegmentsandoneithersideofpharynxand'oesophagus.
•Nephrostomesarealsoabsentinthepharyngealnephridia.
•Ineachbunchtheterminalductsofthenephridiajointogethertoformaslenderduct.
•Theslenderductsagainuniteineachsegmentandformathick-walledductwhichopensintothe
alimentarytube.
•Thustherearethreepairsofducts,onepaireachinthe4th,5thand6thsegments.
•Thepharyngealnephridiahavedigestivefunctionor,inotherwords,theyaidindigestionandhence
theyaresome-timesreferredtoas'pepticnephridia'.
•Theseptalandpharyngealnephridiaopenintothealimentarycanalandarecalledenteronephric
whiletheintegumentarynephridiaopentotheoutsidedirectly,andarecalledexonephric.
•Theenteronephricsystemhelpsintheconservationofwaterinthebodybecausewaterpresentinthe
excretoryProductisagainreabsorbedintheintestine.
•Someofthenitrogenousexcretorysubstanceslikeguaninareextractedfromthebloodstreamby
chloragogencells.
•Thesecellscollectandstoreexcretoryproductsandonbecomingheavilyladenwithexcretory
materials,theypinchoffintothecoelomicfluidfromwheretheyareeliminatedthroughdorsalpores
orbynephridiopores.

13. Excretion in Leech
•Excretorysystemconsistsofnephridia.
•Thereareseventeenpairsofnephridiaonepaireachin6thand22ndsegments.
•Thusthefirstfivesegmentsandtheposteriorfoursegmentsaredevoidofnephridia. Ofthese
seventeenpairs,theanteriorsixpairslieinthepre-testicularsegmentsandarecalledpre-testicular
nephridiaandtheremainingelevenpairsinthetesticularsegments,arecalledtesticularnephridia.
Structureofatesticularnephridium
Atypicaltesticularnephridiumconsistsof:
•Mainlobe
•Apicallobe
•Initiallobe
•Ciliatedorgan
•Innerlobe
•Vesicleductandvesicle

15. (a)Mainlobe
•Itisahorse-shoe-shapedstructureandventro-lateralinposition.
•Themainlobeconsistsoftwounequallimbs,anteriorandposterior.
•Theanteriorlimbislargerinsizethantheposteriorandthetwotogetherattheirjunctionform
thebendofthehorse-shoe.
(b)Apicallobe
•Theposteriorlimbofthemainlobepassesforwardtoformthestoutapicallobe.
•Itliesinanantero-posteriorpositionbeneaththegut.
•Itsanteriorendisbentuponitself.
(c)Initiallobe
•Itrunsasanextremelylongandslenderlobetwinedroundtheapicallobe.
•Atitsanteriorextremityitrunsasaslenderthreadofcellstowardsthetestissacandends
abruptlybythesideoftheperinephrostomialampulla.
•Whileatitsposteriorextremityitjoinsthemainlobenearthepointofemergenceofthevesicle
duct.

16. (d)Ciliatedorgan
•Theciliatedorganliesintheperi-nephrostomialampulla.
•Itisacompoundstructuremadeupofacentralreservoirandciliatedfunnels.
•Thereservoirisspongyinnature.
•Theciliatedfunnelsarepresentinalargenumberonthewallofthereservoir.
•Eachfunnelislikeanear-lobehavingabroaddistalendandaproximalneckwhichfitsintopores
situatedonthewallofthereservoir.
•Thefunnelismadeoffivetosixcellsarrangedintwotiersandisdenselyciliated.
•Theciliatedorganhasnoexcretoryroleinadultleechesandisassociatedwithhaemocoelomic
system.
(e)Innerlobe
Itliesintheinnerconcavityofthemainlobeandrunsforwardalongtheouterborderoftheapical
lobeabouthalfitslength.

17. Route of central canal inside the nephridium
•Thecentralcanalfollowsalongandzigzagcoursethroughoutthebodyofthenephridium.
•Itmakesonecompleteandanotherincompleteroundofruninsidethebodyofthenephridium.
•Thecanalbeginsasalargeintracellularlumeninasinglecellattheanteriorendoftheapical
lobe.
•Thenitcomesdowntheapicallobetoentertheinnerlobefromwhereitgoesoftheposterior
borderoftheanteriorlimbofthemainlobe.
•Fromthemainlobe,itpassesalongtheouterborderoftheapicallobeandonbeingembeddedin
itcompletesthefirst'round'.
•Thecanalthenloopsbackwardandtraversestheapicallobe.
•Onreachingtheposteriorlimitoftheapicallobeitpassesontotheposteriorlimbsofthemain
lobe.
•Aftertraversingthemainlobeandformingmanyloopsinitthecanalemergesfromtheposterior
lipoftheanteriorlimbandcontinuesintothevesicleasvesicleduct.
•Thesecondpartofthecanalisincompletebyone-fourth'round' .

18. Roleofnephridiumandciliatedorgan
•Inthebodyofleechthehaemocoelomicfluid,i.e.,bloodandcoelomicfluid,arenotpresentas
separate,entitiesastheyareinearthworm.
•Theciliatedorganthoughconsideredalongwithexcretorystructuresistotallyseparatedfrom
nephridiuminanadultleech.
•Theciliatedorganbathesinhaemocoelomicfluidandhasnoexcretoryrole.
•Itissubservienttohaemocoelomicsystemandmanufactureshaemocoelomiccorpuscles.
•Whilethebodyofthenephridiumminustheciliatedorganisrichlysuppliedwithlateralchannels,
itisexcretoryandosmoregulatoryinfunctions.
•ManyworkersbelievethattheBotryoidaltissuesareexcretoryinnature.

19. Physiology of Excretion in annelids
•Inmostannelids,thebloodvascularsystemandcoelom(ifpresent)areinvolvedintheexcretion
ofwasteproducts.
•Thepolychaetesinwhichtheblood-vascularsystemisabsentorreducedcontainprotonephridia.
•Theremaininggroupsofpolychaetesandotherspossessblood-vascularsystemand
metanephridia.
•Inproto-nephridia, theultra-filtrationofthecoelomicfluidtakesplacewiththehelpofterminal
cells(e.g.solenocytes)andthefiltratefluidpassesdownthroughtheprotonephridialtubule.
•Alongtheprotonephridialtubulesomesubstancessuchassaltsandaminoacidsarereabsorbed
andthechiefexcretoryproductammoniaisexcretedthroughthenephridiopore.
•Themouthofmetanephridiumcontainsopenciliatedfunnelornephrostomethroughwhich
coelomicfluidisdrawnbytheactionofciliaoffunnelandthefluidwhenpassingthroughthe
metanephridiumtubule,somesubstanceslikesalts,aminoacidsareresorbedandthe
nitrogenouswasteproductslikeammonia(20%),aminoacidsandurea(40%)areexcretedand
theurealevelvariesindifferentgroupsofannelidsinwhichenvironmenttheylive.

21. Functionsofnephridia
(i)Iteliminatestheliquidnitrogenouswasteproductsfromthebodytotheexterior.
(ii)Iteliminatesthebasicandnon-volatileacidradicalsfromthebody.
(iii)Itmaintainsthewaterbalanceofthebody.
(iv)Itregulatestheosmoticrelationbetweenthebloodandtissue.
(v)Insomecasestheyactasgonoducts(coelomoducts)byconveyingreproductiveunits.