Embryology Development of Dermatomusculoskeletal System Biology Medic Department

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 (dermisfibroblast) § Somatic Mesoderm +Ventral dermomyotome of somites +Neural crest cells Mesenchyme myogenesis Induction by Myo. D 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

SKIN DEVELOPMENT • Ectoderm Epidermis • Mesoderm mesenchyme Connective tissues in the dermis • Epidermis • 1 st and 2 nd 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 En dochondral bone formation • Signaling mol. BMP-5, BMP-7

Histogenesis of cartilage • 5 thweek mesenchyme condens e 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 • 6 th week chondrification centres appear neural arch+centrum fuse spinous&transverse proc extension oss. Vertebrae begins in the embryonic end by the 25 th year

Ribs 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 1 st malleus incus, - 2 nd stapes+temporal bones, lesser horn, sup sphenoid bone, - 3 rd 4 th, 6 th greater horns+inf part hyoid bone - . 4 th laryngeal cartilages - Membranous: max. prominence squamous, temporal, zygomatic and maxillary, - Mandibular prominence mandible