Embryology of skeletal system

Presentation on embryology of skeletal system

1. EMBRYOLOGY OF
SKELETAL SYSTEM
PRESENTER : DR. BIJAY MEHTA

2. Contents
•Introduction
•Formation of Bones and Cartilages
•Development of Axial Skeleton
•Development of Limbs
•Developmental Malformations

3. •Theskeletalsystemdevelopsfrom
mesenchyme, which is
MesodermalinOrigin.
•Mesenchymeortheembryonic
ConnectiveTissuemigratetoform
•Chondroblasts
•Osteoblasts
•Fibroblasts
Introduction

4. Formation of Bones and Cartilages
•Atasitewherecartilageistobeformed,mesenchymalcellsbecome
closelypacked.Thisiscalledamesenchymalcondensation.
•Themesenchymalcellsthenbecomeroundedandgetconvertedinto
cartilageformingcellsorchondroblasts.
•Undertheinfluenceofchondroblasts,theintercellularsubstanceof
cartilageislaiddown.
•Mesenchymalcellssurroundingthesurfaceofthedeveloping
cartilageformafibrousmembrane,theperichondrium.

5. Ossification
•Bone develops through two
types of ossifications:
•Membranous Ossification, in
which mesenchymal tissues will
directly convert into bone ,eg
flat bones of the skull.
•Endochondral Ossification, in
which mesenchymal tissues
first give rise to hyaline
cartilaginous model of the
bone and then, the osteoblasts
convert them into the bone,eg
Long bones, Vertebra.

6. •Subdivisionsof intraembryonic
mesodermareparaxialmesoderm,
intermediatemesodermandlateralplate
mesoderm.
•ParaxialMesodermformsasegmented
seriesoftissueblockoneithersideof
theNeuraltube,theSomites.
•TheseSomitesdifferentiateinto:
•dermatomewhichformsthedermisofthe
skin;
•myotomewhichformsskeletalmuscle;
•sclerotomewhichhelpstoformthe
vertebralcolumnandribs.
Formation of Axial Skeleton

7. •Thevertebralcolumnand
ribsdevelopfromthe
sclerotomecompartmentsof
thesomites,andthesternum
isderivedfrommesodermin
theventralbodywall.
•Adefinitivevertebrais
formedbycondensationof
thecaudalhalfofone
sclerotomeandfusionwith
thecranialhalfofthe
subjacentsclerotome.
Vertebra

8. •Atypicalvertebraconsistsofa
vertebralarchandforamen
(throughwhichthespinalcord
passes),abody,transverse
processes,andusuallya
spinousprocess.
•Duringthefourthweek,
sclerotomecellsmigrate
mediallyandsurroundsthe
notochord.
•Themesenchymethenextends
backwardoneithersideofthe
neuraltubeandsurroundsit.

9. •Extensionsofthismesenchymealsotakeplacelaterallyforming
transverseprocesses,andventrallyinthebodywall,formingribs.
•Mesenchymalcellsfromthesclerotomes,alsomigratecraniallyto
surroundthenotochord,wheretheyformtheintervertebraldisc.
•Asdevelopmentprogresses,thenotochorddegeneratesand
disappears.
•Betweenthevertebrae,thenotochordexpandstoformthe
gelatinouscentreoftheintervertebraldisc–thenucleuspulposus.
•Thisnucleusislatersurroundedbycircularlyarrangedfibresthat
formtheanulusfibrosus.
•Theanulusfibrosusandnucleuspulposustogetherconstitutethe
intervertebraldisc.

10. Ribs and Sternum
•Ribs are formed from the ventral extensions of the sclerotomic
mesenchyme that form the vertebral arches.
•The Sternum is formed from the two sternal bars on either side of the
midline.

11. Formation of Limbs
•Thebonesofthelimbs,
includingthebonesofthe
shoulderandpelvicgirdles,
areformedfrommesenchyme
ofthelimbbuds.
•Withtheexceptionofthe
clavicle(whichisamembrane
bone),theyareallformedby
endochondralossification.

12. •Thelimbbudsarepaddle-shapedoutgrowthsthatarisefrom
thesidewalloftheembryoatthebeginningofthe2nd
monthofintrauterinelife.
•Eachbudisamassofmesenchymecoveredbyectoderm.
•Themesenchymeoflimbbudsisderivedfromtheparietal
layerofthelateralplatemesoderm.Thismesenchymegives
risetobones,connectivetissueandsomebloodvessels.The
musclesofthelimbsarederivedfrommyotomesofsomites
whichmigrateintothelimbs.

13. •Theforelimbbudsappearalittle
earlierthanthehindlimbbuds.As
eachforelimbbudgrows,it
becomes subdivided by
constrictionsintoarm,forearmand
hand.Thehanditselfsoonshows
outlinesofthedigits.
•Theinterdigitalareasshowcell
deathbecauseofwhichthedigits
separatefromeachother.Similar
changesoccurinthehindlimb.
•Whilethelimbbudsaregrowing,
themesenchymalcellsinthebuds
formcartilaginousmodels,which
subsequentlyossifytoformthe
bonesofthelimb.

15. •The limb buds are at first directed forward and laterally from the body
of the embryo . Each bud has a preaxial (or cranial) border and a
postaxial border. The thumb and great toe are formed on the preaxial
border.
•The forelimb bud is derived from the part of the body wall belonging
to segments C4, C5, C6, C7, C8, T1 and T2. It is, therefore, innervated
by the corresponding spinal nerves.
•The hindlimb bud is formed opposite the segments L2, L3, L4, L5, S1
and S2.

16. Formation of Joints
•Thetissuesofjointsarederivedfrommesenchymeintervening
betweendevelopingboneends.Thismesenchymemay
differentiateintofibroustissue,formingafibrousjoint
(syndesmosis),orintocartilageformingacartilaginousjoint.Inthe
caseofsomecartilaginousjoints(synchondrosisorprimary
cartilaginousjoints),thecartilageconnectingthebonesislater
ossified,withtheresultthatthetwobonesbecomecontinuous.
•Thisisseen,typically,atthejointsbetweenthediaphysesand
epiphysesoflongbones.

17. •Atthesitewhereasynovialjointis
tobeformed,themesenchymeis
usuallyseeninthreelayers.
•Thetwoouterlayersare
continuous with the
perichondriumcoveringthem
cartilaginousendsofthe
articulatingbones.
•Themiddlelayerbecomesloose
andacavityisformedinit.The
cavitycomestobelinedbya
mesotheliumthatformsthe
synovialmembrane.The
capsuleandotherligamentsare
derivedfromthesurrounding
mesenchyme.

18. Anomalies of the Vertebra
•Absent Vertebra
•Parts of Vertebra may be absent
•Spina Bifida
•Hemivertebra
•Sacrococcygeal teratoma
•Congenital Scoliosis
•Fusion of Vertebra : In the cervical region,
Occipitalioztion of Atlas, in the lumbosacral
region,sacralization of the lumbar Vertebra.

19. Anomalies of Sternum and Ribs
•Missing Ribs
•Additional Ribs
•Pigeon Chest
•Funnel Chest

20. Anomalies of the Limbs
•Phocomelia
•Clubfoot(CTEV)
•Syndactyly
•Polydactyly
•Achondroplasia

21. Timetable for some events

22. References:
•Langman’sMedical Embryology, Fourteenth Edition.
•InderbirSingh’s Human Embryology, Eleventh Edition.
•Various Websites

23. Thank You