1. Embryology Development of Dermatomusculoskeletal System
Biology Medic Department
2011

2. 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
Fibroblastperimysium and epimysium
Dev before birth, sizediameter fiber, length&wide to grow with skeleton

3. Myotomes
1. 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 musclesextrinsic eye muscles
Myoblast surrounding the developing boneslimb muscles
Occipital myotomTongue Muscles

4. SKIN DEVELOPMENT EctodermEpidermis
MesodermmesenchymeConnective tissues in the dermis
Epidermis
1st and 2nd trimesters of pregnancythickness
PrimordiaEctodermal cells at 4 weeks Proliferation (Periderm) & Basal/germinativum layer
Basal layerStr, germinativumproduced more cell to superficial layerIntermediate layer (11 weeks)
Epidermal ridgesgrooves(10-17 weeks)
Peridermkeratinization,desquamation(Vernix caseosa)--<Str, Corneum (21 weeks)
Ektoderm  Neural crest cellmigrate into the mesenchyme of the developing dermis Melanoblastmigrate to dermoepdermal junctionMelanocyte

5. Glands of The Skin Development
1. Sebaceous Gland
Derived from the epidermis to dermis
( develop from epithelial root sheath of hair follicleprimordiacentral alveoli ruptureoil excretion)

6. Glands of The Skin Development
2. Sweat Glands
Epidermal down growth to the mesenchyme
Cellular bud of sweat glandelongate Central cell degenerate lumentheperipheral cells secretory & Myoepithelial cells

7. Hair Follicles Development
Proliferation of str. Germinativum to the dermishair budshair bulb(primordia) epithelial cells(germinal matrix)produces hair
Hair bulbs  invaginated by small mesenchyme hair pappillae
The peripheral cellsepithelial root sht.
Surrounding messenchymal diff. cellsdermal root sht.
Arrector m. attach to the dermal root

8. Skeletal System Development
Sclerotomevertebrae & ribs.
Mesodermal cellsmesenchym(Embryonic con. tissue)condensation (gene act.)osteogenesis
Mesenchymepre existing membranous sheaths Intramembranous bone formation
MesenchymalcartilagesEndochondral bone formation
Signaling mol.BMP-5,BMP-7

9. Histogenesis of cartilage
5thweekmesenchymecondensechondrification centres diff. chondroblast  collagenous fibril&ground substance(ECM).
Histogenesis of Bone
Intramembranous Ossification  mesenchyme condenseshighly vascular  some cells diff.osteoblast & deposit unmineralized)  osteon matrix (osteoid) osteocytesSpicules of bone concentric lamella(layers)
Endochondral Ossificationcartilagelong bone(primary centres-diaphysis)  chondrocytes hypertrophythe matrix calcified centre cells die  periosteum invasion by vasc. conn,.Tissuesome cells diffhemopoetic cells.
Lengthening growth platesSec. oss.in the epiphysisfew years after birth
Ossification of limb bonesat the end of the embryonic perioddemands supply Ca&P

10. Development of Vertebral Column
Mesenchymal cellssclerotomes3 main areas: around notochord, neural tube and body wall.
Frontal sectpaired condensation of mesenchymal areas around notochordloosely arr. Cranially& densely packed cells caudally.
Some densely packed cellsmove craniallyooposite the centres of myotomesIv disc
The remaining cells fusecentrumbody of vertebrae( each centrum dev from 2 sclerotomesintersegmental structuresinter. A. lie in each side vert. bodies.

11. Development of Vertebral Column…
Notochord degeneratesgelatinous centrenucleus pulposus
Surroundedcircularly arranged fiberannulus fibr.
Messenchymal cells surrounding neural tubeneural a
6th weekchondrification centres appearneural arch+centrum fusespinous&transverse procextensionoss. Vertebrae begins in the embryonicend by the 25th year

12. Ribs Development Sternum Development
Mesenchymal costal procoriginal site of union costal pros with vertreplacedcostovertebral synovial joints
Sternum Development
A pair of vertical mesenchymal bands(sternal bars)develop ventrolaterallymove mediallychondrificationfuse craniocaudallyformmanubrium, sternebrae&xiphoid proc(oss.childhood) .

13. Development of Vertebral Column
Mesenchymal cellssclerotomes3 main areas: around notochord, neural tube and body wall.
Frontal sectpaired condensation of mesenchymal areas around notochordloosely arr. Cranially& densely packed cells caudally.
Some densely packed cellsmove craniallyooposite the centres of myotomesIv disc
The remaining cells fusecentrumbody of vertebrae( each centrum dev from 2 sclerotomesintersegmental structuresinter. A. lie in each side vert. bodies.

14. Development of the Cranium
Develop from mesenchyme arround the developing brain, consist of:
- The neurocraniumprotective case for the brain
Cartilaginous base of craniumfusionendochondral osssequence:occ.bone, sphenoid, ethmoid
Membranous neurocranium:
Intramembranous oss. messenchyme arround & top of the braincalvariafontanelles(suture meet)

15. The viscerocranium skeleton of the face
Cartilaginous: neural crest cellsmigrtaes from pharyngeal arches.Hox 1stmalleus incus,
2nd stapes+temporal bones,lesser horn,sup sphenoid bone,
3rd 4th,6th greater horns+inf part hyoid bone
.4thlaryngeal cartilages
Membranous:max. prominencesquamous, temporal,zygomatic and maxillary,
Mandibular prominencemandible

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