Dr Jamila EL Medany
Dr Jamila EL Medany
OBJECTIVES
Attheendofthelecture,studentsshouldbeableto:qListthedifferentpartsofmesodermandthedifferentdivisionsofsomites.
qDifferentiatebonesaccordingtotheirembryologicaloriginandmodeofossification.
qDescribetheossificationoflongbones.qDescribethemainstepsfordevelopmentoflimbs.qDifferentiatemusclesaccordingtotheirembryologicalorigin.
Amnioticcavity
Yolksac
Embryo
Embryo
Notochord:stimulatesneuraltubeformation
Somaticmesoderm
Splanchnic mesoderm
INTRAEMBRYONIC MESODERMqProliferatesbetweenEctoderm&EndodermEXCEPT inthecentralaxisofembryowhereNOTOCHORD isfound.
qDifferentiatesinto3parts:1. Paraxialmesoderm:oneachsideofnotochord.2. Intermediatemesoderm3. LateralmesodermqParaxialmesodermdividesintounits(Somites).qLateralmesodermdividedbyintraembryonic coelominto:
1. Somaticmesoderm(betweenectoderm&coelom).2. Splanchnic mesoderm(betweenendoderm&coelom).
SOMITE SOMITE
Notochord
SclerotomeSclerotome
Neuraltube
Myotome
qVertebralcolumnqRibs&sternum
Epaxial division:Musclesofback
(ExtensorsofVC&Neck)
Hypaxial division:Musclesofbodywall
Myotome
Myoblasts migrateintolimb:
Limbmuscles
Myoblasts migrateintolimb:
Limbmuscles
Epaxial division:Musclesofback
(ExtensorsofVC&Neck)
DEVELOPMENT OF LIMBS - 1
28DAYS
32DAYS
qThelimbBudappearsasanelevationontheventrolateralbodywallresultingfromproliferationofmesenchymeofthesomaticlayeroflateralmesoderm.qEachlimbbudissurroundedbyanareaofectoderm.qUpperlimbbudsqAppearatday26 oppositethelowercervical segments.qLowerlimbbudsqAppearatday28oppositethelumbar&sacralsegments.
DEVELOPMENT OF LIMBS - 2
qA&G:Apicalectodermal ridge:appearsattheapexoflimbbudandstimulatesproliferationofmesenchyme andelongationoflimbbud.
qB&H:Distalendsofbudsflattenintopaddle-like hand&footplates.
qC&I:Digitalrays:appearasmesenchymal condensationsthatoutlinethepatternsofdigits.
qD&J:Notches:appearbetweendigitalrays.q E&K:Digitsforminsiderays,elongate&appearwebbed.q F&L:Mesenchyme betweendigitsdisappeartoseparate
them.
DEVELOPMENTOFLIMBS - 3
qOriginally,limbbudswereatrightangleofthetrunkwith:-Cranial(preaxial)&Caudal(postaxial) borders:radius andtibia arepreaxial bones.-Ventral&Dorsal surfaces:flexormusclesareventral.
qDuring7th week,adductionoflimbbudsoccurswith90°rotation:-Inupperlimb, rotationoccurslaterally:radiusislateral&flexormusclesareanterior.-Inlowerlimb,rotationoccursmedially: tibiaismedial&flexormusclesareposterior.
Mesenchyme fromlateralmesoderm
Inducesgrowthofmesenchyme &itstransformationintocartilage
Cartilageossifiesby:Endochondral ossification
Myoblasts migratefrommyotomes toform:Musclesoflimbs
Boneincartilaginousstate
Appearanceofprimaryossificcenters:ossificationofdiaphysis
Appearanceofsecondaryossificcenters:ossificationofepiphysis
Ossificationofepiphseal plate:Completeunionofepiphysis&diaphysis
Diaphysis
Epiphysis
Epiphysealplateofcartilage
BIRTH PUBERTY
Diaphysis
Boneincreasesinlengthbyproliferationofepiphyseal plate
Growthofbonestops
OSSIFICATIONOFLONGBONES
Boneageisagoodindexofgeneralmaturation.Boneageisdeterminedby:1. Appearanceofossific centersindiaphysis &epiphysis(specificforeachbone&sex)2. Disappearanceofepiphyseal plate(specificforeachbone&sex)
Epiphysis
DEVELOPMENT OF CRANIUM (SKULL)
qThe skull develops from mesoderm around the developing brain.
qThe skull consists of:1. Neurocranium: protective case for brain2. Viscerocranium: skeleton of faceq Bones of skull ossify either by:
*Endochondral ossification or*Intramembranous ossification
12
FP
ST Z MaxMand
F
F
F
P
P
Bonesofskullthatossifybyintramembranous ossification:1. F=Frontal2. P=Parietal3. Z=Zygomatic4. ST=Squamous temporal5. Mand =Mandible6. Max=Maxilla
JOINTS
Theydevelopfrommesodermbetweenbones:qFibrousjoints:mesodermdifferentiatesintodensefibrousconnectivetissue.
qCartilaginousjoints:mesodermdifferentiatesintocartilage.
qSynovialjoints:asynovialcavityisformedinsidemesoderm;mesodermdifferentiatesintosynovialmembrane,capsule &ligaments.
SUMMARYOFDEVELOPMENTOFBONE
All bones develop from MESODERM.qAXIAL SKELETON:
*Vertebrae, Ribs & Sternum: from Sclerotomes of Somites (Paraxial Mesoderm)*Skull: from Mesoderm surrounding the Brain
qAPPENDICULAR SKELETON: from Somatic part of Lateral Mmesoderm
All bones ossify by Endochondral Ossification EXCEPT:
1. Some bones of Skull2. Clavicle
SUMMARY OF DEVELOPMENT OF MUSCLES
qAllmuscles developfromMESODERM EXCEPT:1. Musclesofiris(eyeball)2. Myoepithelial cellsofECTODERM
mammary&sweatglandsq Allskeletalmusclesdevelopfrommyotomes
ofparaxialmesoderm EXCEPT:q someHead&Neckmusclesfrommesoderm
ofPharyngealArches
SUMMARY OF DEVELOPMENT OF MUSCLES
qCardiac&Smoothmusclesdevelopfromlateralmesoderm:
1. Cardiacmusclesfrom:splanchnic partoflateralmesoderm
2. Smoothmuscles:*Inthewallofviscerafrom:splanchnic partoflateralmesoderm*Inthewallofblood&lymphaticvesselsfrom:somaticpartoflateralmesoderm
QUESTION1
qWhichoneofthefollowinggroupofmusclesarederivativesofepaxial divisionofmyotomes?
1. Musclesofback2. Musclesoflimbs3. Musclesofviscera4. Cardiacmuscles
QUESTION2
q Whichoneofthefollowingbonesossifiesbyintramembranous ossification?
1. Vertebra2. Humerus3. Ribs4. Mandible
QUESTION3
qRegardingtheossificationoflongbones,whichoneofthefollowingstatementiscorrect?
1. Primaryossific centreappearsafterbirth.2. Secondaryossific centreleadsinto
ossificationofdiaphysis.3. Longbonesossifybyintramembranous
ossification.4. Whenepiphysisuniteswithdiaphysis,
growthofbonestops.
THANK YOU