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Embryology Development of
Dermatomusculoskeletal System
Biology Medic Department2011
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SKELETAL MUSCLE DEVELOPMENT
The Muscular system mesoderm(exc. iris musc.neuroectoderm, esop.musc. smooth musc.)
Paraxial Mesoderm somites A. Ventromedial (Sclerotome)
Vertebrae+ribs B. Dorsolateral (Dermomyotome)
myotome (myoblast) + dermatome (dermis-fibroblast)
Somatic Mesoderm +Ventral dermomyotome of somites +Neural crest cells Mesenchyme myogenesis Induction by MyoD gene elongation of the nuclei& cell bodies Myoblast myotubes+ myofilament+ myofibril invested with ext.lamina.endomysium
Fibroblastperimysium and epimysium Dev before birth, sizediameter fiber,
length&wide to grow with skeleton
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Myotomes1. Epaxial the extensor muscles of
the neck & vertebral column, Caudal myotom regressed
2. Hypaxial cervical myotomes scalene, pravertebral, geniohyoid & infrahyoid m.
• thoracic myotomes lateral and ventral flexor muscles of the vertebral column
• lumbar myotomes quadratus lumborum m.
• Pharyngeal arch m. facial expression,m. of mastication, pharynx and larynx
• Mesenchymal cells near the prechordal plate Ocular musclesextrinsic eye muscles
• Myoblast surrounding the developing boneslimb muscles
• Occipital myotomTongue Muscles
•
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SKIN DEVELOPMENT• EctodermEpidermis• MesodermmesenchymeConnective tissues in
the dermis• Epidermis• 1st and 2nd trimesters of pregnancythickness• PrimordiaEctodermal cells at 4 weeks
Proliferation (Periderm) & Basal/germinativum layer• Basal layerStr, germinativumproduced more
cell to superficial layerIntermediate layer (11 weeks)
Epidermal ridgesgrooves(10-17 weeks)
• Peridermkeratinization,desquamation(Vernix caseosa)--<Str, Corneum (21 weeks)
• Ektoderm Neural crest cellmigrate into the mesenchyme of the developing dermis Melanoblastmigrate to dermoepdermal junctionMelanocyte
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Glands of The Skin Development
1. Sebaceous Gland• Derived from the
epidermis to dermis
• ( develop from epithelial root sheath of hair follicleprimordiacentral alveoli ruptureoil excretion)
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Glands of The Skin Development
2. Sweat Glands• Epidermal down growth
to the mesenchyme• Cellular bud of sweat
glandelongate Central cell degenerate lumentheperipheral cells secretory & Myoepithelial cells
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Hair Follicles Development• Proliferation of str.
Germinativum to the dermishair budshair bulb(primordia) epithelial cells(germinal matrix)produces hair
• Hair bulbs invaginated by small mesenchyme hair pappillae
• The peripheral cellsepithelial root sht.
• Surrounding messenchymal diff. cellsdermal root sht.
Arrector m. attach to the dermal root
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Skeletal System Development
• Sclerotomevertebrae & ribs.• Mesodermal
cellsmesenchym(Embryonic con. tissue)condensation (gene act.)osteogenesis
• Mesenchymepre existing membranous sheaths Intramembranous bone formation
• MesenchymalcartilagesEndochondral bone formation
• Signaling mol.BMP-5,BMP-7
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Histogenesis of cartilage• 5thweekmesenchymecondensechondrificati
on centres diff. chondroblast collagenous fibril&ground substance(ECM).
Histogenesis of Bone• Intramembranous Ossification
mesenchyme condenseshighly vascular some cells diff.osteoblast & deposit unmineralized) osteon matrix (osteoid) osteocytesSpicules of bone concentric lamella(layers)
• Endochondral Ossificationcartilagelong bone(primary centres-diaphysis) chondrocytes hypertrophythe matrix calcified centre cells die periosteum invasion by vasc. conn,.Tissuesome cells diffhemopoetic cells.
• Lengthening growth platesSec. oss.in the epiphysisfew years after birth
• Ossification of limb bonesat the end of the embryonic perioddemands supply Ca&P
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Development of Vertebral Column
• Mesenchymal cellssclerotomes3 main areas: around notochord, neural tube and body wall.
• Frontal sectpaired condensation of mesenchymal areas around notochordloosely arr. Cranially& densely packed cells caudally.
• Some densely packed cellsmove craniallyooposite the centres of myotomesIv disc
• The remaining cells fusecentrumbody of vertebrae( each centrum dev from 2 sclerotomesintersegmental structuresinter. A. lie in each side vert. bodies.
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Development of Vertebral Column…
• Notochord degeneratesgelatinous centrenucleus pulposus
• Surroundedcircularly arranged fiberannulus fibr.• Messenchymal cells surrounding neural tubeneural a• 6th weekchondrification centres appearneural
arch+centrum fusespinous&transverse procextensionoss. Vertebrae begins in the embryonicend by the 25th year
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Ribs Development
• Mesenchymal costal procoriginal site of union costal pros with vertreplacedcostovertebral synovial joints
Sternum Development• A pair of vertical mesenchymal bands(sternal
bars)develop ventrolaterallymove mediallychondrificationfuse craniocaudallyformmanubrium, sternebrae&xiphoid proc(oss.childhood)
• .
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Development of Vertebral Column
• Mesenchymal cellssclerotomes3 main areas: around notochord, neural tube and body wall.
• Frontal sectpaired condensation of mesenchymal areas around notochordloosely arr. Cranially& densely packed cells caudally.
• Some densely packed cellsmove craniallyooposite the centres of myotomesIv disc
• The remaining cells fusecentrumbody of vertebrae( each centrum dev from 2 sclerotomesintersegmental structuresinter. A. lie in each side vert. bodies.
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Development of the Cranium
• Develop from mesenchyme arround the developing brain, consist of:
- The neurocraniumprotective case for the brain
Cartilaginous base of craniumfusionendochondral osssequence:occ.bone, sphenoid, ethmoid
Membranous neurocranium:
Intramembranous oss. messenchyme arround & top of the braincalvariafontanelles(suture meet)
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- The viscerocranium skeleton of the face
- Cartilaginous: neural crest cellsmigrtaes from pharyngeal arches.Hox 1stmalleus incus,
- 2nd stapes+temporal bones,lesser horn,sup sphenoid bone,
- 3rd 4th,6th greater horns+inf part hyoid bone
- .4thlaryngeal cartilages- Membranous:max.
prominencesquamous, temporal,zygomatic and maxillary,
- Mandibular prominencemandible
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