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S-BIOL429LA Dev Bio Lab MEB34 2nd Sem ( 2023-2024 )
MODULE 8 - Gastrulation & Neurulation
Gastrulation and Neurulation (Introduction)
Immersive Reader
Following the blastula stage is the gastrulation and then neurulation. In gastrulation the three germ layers form
around the embryo preparing the embryo organogenesis wherein the various body organs are created.
Amphibian gastrulation involved the processes of invagination, involution and epiboly in the formation of the
germ layers. In chick embryo, gastrulation occurs after the formation of the hypoblast. Pregastrulation involve the
hypoblast formation by delamination process or polyingression. This fertilized chicken egg is usually laid during
the stage of hypoblast formation. Primitive streak formation marks the start of gastrulation process.
Neurulation is the process where the embryo is forming the neural tube or the primordium of the nervous system
18. Module 6
Gastrulation and Neurulation
Procedure
1. View theprepared slides (photomicrographs) of thefrog’sembryonicdevelopmentusing thescanner
and LPO.
1. Identifythe structuresof the gastruladescribedbelow.
Gastrula.Thisis usuallythe formationof acup or sac-shaped,twolayeredwallsof cellssurrounding
a cavity,the archenteron.
Archenteron.Itis the innertube linedwithmesentodermal cellsandisultimatelylinedwith
endodermal cellsatlate gastrulation. Itscavityiscalledthe gastrocoel.
Blastopore.It isthe external openingof the archenteron.
Dorsal lip.It isthe well-defineduppermarginof the blastopore.
Ventral lip.It isthe lowermarginof the blastopore.
Yolkplug.It is a mass of large yolkycellsthatblockthe blastopore whichsometimesappearsas
protrudingstructure tothe blastopore.
Ectoderm.It is the outermostlayerof cellsinvestingthe gastrula.
Mesoderm.Itisthe layerof cellsatthe roof of the archenteron.
Endoderm.It isthe layerof cellsatthe floorof the archenteronandislocatedinnermost.
Blastocoel.Itis the narrow space betweenarchentericroof andthe ectoderm.Onlyitsremnants
are seen.
Fertilizationmembrane.Itisstill presentenvelopingthe gastrula.Thisislooselyappliedtothe
gastrulathan to the blastula.
Earlygastrula
21. 2. Identifythe structuresof the frogneuruladescribedbelow.
Neurula.Thisisthe embryonicstage whichfollowsgastrulationprocess.Thisisthe stage during
whichthe neural tube or primordiumof the central nervoussystemisformed.
Ectoderm.This outermostlayerisveryevidentonthisstage,investingonthe otherparts.
Neural (medullary) plate.Itis a dorsal thickenedplate of ectodermal cells.In
the earlystage of the neurula,thisplate isrelativelyflattenedinshape andis
boundedonbothsidesbya lowridge.
Neural fold.It isan elevationof the ectodermallayeratthe sidesof the thickenedanddepressing
neural plate.
Neural tube.It isthe plate whichhasbeenfoldedintoatube withthe fusioninthe midline of the
neural folds.
Neurocoel.Itthe cavityof the neural tube.Thisisformedsimultaneouslywiththe closure of the
neural folds.
Mesoderm.Itisa flatlayerinearlyneurulabeneaththe neural platewithcurved lateral wings
extendingdownwardoneachside of the embryo.Itislocatedbetweenthe endodermal andectodermal
22. layers.Thismesoderminthe late neurulawill differentiateintonotochord,somites,lateral platesor
hypomere andnephrotome.
Neuralplate stage
Notochord.It isthe roundedmassof mesodermal cellslyinginthe midlinedirectlybeneaththe
neural plate.
Somites/Epimere.Theyare blocksof mesodermalcellsflankingthe notochordoneachside and
lyingbeneaththe lateral partsof the neural plate.
Lateral plate/hypomere.Itisthe remainderof the mesodermthatwill eventuallymeetandfuse at
the mid-ventral line.
Nephrotome/mesomere.Itisa narrow regionof the mesodermbetweenthe somite andthe lateral
plate.Itis alsoa termedas intermediate mesoderm.
Coelom.Itisa narrowcleftformedfromthe splittingof the mesoderm.
Endoderm.It isa layerof large massof cellsheavilyladenwithyolksurroundingthe definite
archenteron,the central cavity(gastrocoel).
Fertilizationmembrane.Itisthe loose envelope aroundthe neurula.
Gutcavity (Gastrocoel).Itis the cavityformedbythe innertube whichislinedwithendodermal
cells.
.
3. Answeritems1-2inthe worksheet.
Neural plate stage
26. 2. View theprepared slides (photomicrographs) of thechickembryonicdevelopmentusing thescanner
and LPO.
1. Identifythe structuresof the primitivestreak(gastrula)stage (15-18 hrs.incubationchick
embryo) describedbelow.
Area pellucida.Thisisthe lighter,centrallylocatedandpear-shapedregionof the blastoderm.This
consistsof an outerlayerof epiblastandinnerlayerof hypoblast(endoderm).
Area opaca. It isthe darkerand denserregionaroundthe areapellucida.
Primitive streak.It isslightlythickerstreakof cellslyinginthe mainaxisof the
areapellucida.Itconstitutesthe primitive grooveandprimitive folds.
Primitive groove.The isthe slightdepressionwiththinflooratmiddle of the primitivestreak.
Primitive ridgesor folds.These are low ridgesinthe blastodermoneachside of the primitive
groove.
Primitive knot.It isthe anteriorendof the primitive groove where the blastodermisdeeply
indented
Primitive groove.
Primitive knotor Hensen’snode.Thisisa small darkerregionanteriortothe primitivepit.
.
2. Identifythe structuresof the 18 hourchick embryo(whole mount)describedbelow.
Primitive streak,groove,ridges,pit and knot.Describedinthe previoussection.
27. Head process(notochord).It isa faintstreakanteriortothe primitive pitwhichisformedfromthe
involutionof presumptive notochordatthe Hensen’snode throughthe pitandmovinganteriorly
betweenthe endodermandectoderm.
Neural plate.An ectodermal thickeningthatoverliesthe notochord.Itmaynot be visible inthe
whole mounts
Head fold(Cranial fold).At thisthisitis a distinctcurvedline justanteriortothe tipof the head
process.Thinsline indicatesthe startof the formationof the cranial boundaryof the head.
Neural groove and neural tube. May have formedinthe headregionandshort insize.
Mesoderm.The partof the blastodermthatcontainmesodermbetweenthe ectodermand
endodermare slightlydarker.
Proamnion.It isa clearregionof the area pellucidaanteriortothe borderof the mesoderm.Itis
composedof ectodermandendodermlayer.
3. Identifythe structuresof the 18 hourchick embryo(serial sections) andidentifythe following:
neural plate,neural groove,neural fold, notochord, ectoderm, mesoderm,endoderm,primitive
groove and primitive streak.
