Embryology Development of

Dermatomusculoskeletal System

Biology Medic Department2011

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

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

•

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

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)

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

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

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

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

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.

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

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)

• .

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.

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)

- 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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