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Intraembryonic mesoderm
The document discusses the development of the mesoderm germ layer during embryogenesis. It notes that the mesoderm initially forms three layers - paraxial, intermediate, and lateral plate mesoderm. The paraxial mesoderm segments into somites which further differentiate into sclerotome, myotome and dermatome tissues. The intermediate mesoderm forms urogenital structures while the lateral plate mesoderm splits into somatic and splanchnic layers which give rise to various tissues like muscle, bone, blood and connective tissues.
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Intraembryonic mesoderm
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- 7. Somitomeres •Eachsomitomereconsistsof mesodermalcellsarrangedin concentricwhorlsaroundthe centeroftheunit. •Intheheadregion,somitomeres form inassociationwith segmentationof theneuralplateintoneuromeresand contribute tomesenchymeinthehead
- 12. Somites •Fromtheoccipitalregioncaudally,somitomeresfurtherorganizeinto somites. •Thefirstpairofsomitesarisesinoccipitalregionat20thday •Newsomitesappearincraniocaudalsequenceatarateof approximatelythree pairsperdayuntil,attheendofthefifthweek, 42to44pairsarepresent •Thereare4-occipital,8-cervical,12-thoracic,5-lumbar,5-sacral,and8-10- coccygealpairs. •Thefirstoccipitalandthelastfivetosevencoccygealsomiteslater disappear, whiletheremainingsomitesformtheaxial skeleton
- 13. Somite Differentiation •Whensomitesfirstformfrom presomitic mesoderm,theyexistas aballof mesoderm(fibroblastlike)cells. •Thesecellsthenundergoaprocess of epithelizationandarrange themselvesina donutshapearound asmalllumen •cellsintheventralandmedialwalls ofthe somitelosetheirepithelial characteristics, become mesenchymal(fibroblastlike) again, andshifttheirpositiontosurround theneuraltubeandnotochordand form thesclerotomethatwill differentiateinto thevertebraeandribs
- 14. SomiteDifferentiation •Cellsatthedorsomedialand ventrolateraledgesoftheupper regionofthesomiteform myotome- •myotome-musculaturefor thebody wallandmostofthelimb muscles •Cellsbetweenthesetwogroups form thedermatome •Dermatome forms dermis and subcutaneousareaof skin.
- 15. •Eachmyotomeanddermatomeretainsitsinnervationfromits segmentof origin,nomatterwherethecellsmigrate. • Hence,eachsomiteformsitsownsclerotome(thetendoncartilageandbone component),itsownmyotome(providingthesegmental musclecomponent),and itsowndermatome,whichformsthedermis oftheback. •Eachmyotomeanddermatomealsohasitsownsegmentalnerve component
- 16. IntermediateMesoderm •Intermediatemesoderm,whichtemporarilyconnectsparaxial mesoderm withthelateralplatedifferentiatesintourogenitalstructures. •In upperthoracic and cervical regions this forms the nephrotomes, and in caudallyregionsthisformsthenephrogeniccord
- 17. LateralPlateMesoderm •Lateralplatemesodermsplitsinto •parietal(somatic)and •visceral(splanchnic)layers, •intraembryoniccavity-inbetween •Theparietallayeroflateralplatemesodermformsdermis,bonesand connective tissueofbodywall. •Mesodermcellsoftheparietallayersurroundingtheintraembryonic cavityform serousmembranes,whichwilllinetheperitoneal,pleural,andpericardialserous membranesandsecreteserousfluid •Hearttube
- 19. Mesodermderivatives • Muscle(smooth,cardiac,skeletal) • Boneandcartilage •Heart,bloodvesselsandbloodcellsofthecirculatorysystem,microglia, andKupffer cells • Endotheliumofbloodandlymphvessels • Connectivetissue,Dermisandsubcutaneouslayerof skin • Duramater • Spleen • Kidney • Adrenalcortex • Testes,epididymis,ductusdeferens,seminalvesicle,ejaculatory duct • Ovary,uterus,uterinetubes,superior1/3ofvagina • Serousmembraneliningthebodycavities
- 20. •Mesenchyme-Aprimordialembryonicconnectivetissue,consisting ofaloose, fluidextracellularmatrixandfewfibresandstellatecells. Canoriginatefromthe mesodermorfromneuralcrest.foundasacomponentofWharton'sjelly. •Mesoderm- Themiddleofthe3germlayers.It givesrisetoall connective tissues(exceptintheheadandneckregions),allbody musculature,blood, cardiovascularandlymphaticsystems,mostof theurogenitalsystemandthe liningofpericardial,pleuraland peritonealcavities.
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