Embryology Development of Dermatomusculoskeletal System Biology Medic Department 2011

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

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

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

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)

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

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

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

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

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.

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

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) .

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.

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)

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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