DEVELOPMENT OF MUSCULOSKELETAL SYSTEM WITH

GENERAL EMBRYOLOGY

DR KIRTI S SOLANKE

stages

• 23 stages-first 8 weeks after ovulation• Streeter(1942) and O'Rahilly & Müller (1987). • Comparing with other embryos

GENERAL EMBRYOLOGY

Primordial germ cell formation

• Gamets –PGC-formed in epiblast during 2nd wk of dev move to wall of yolk sac

• 4th wk migrate from yolk sac-arrive in dev gonad at 5th wk

• For preparation of fertilization ,has to undergo gametogenesis-meiosis-to reduse chromosome no cytodifferentiation-to complete maturation

THE PHASES OF FERTILIZATION INCLUDE

• Phase 1- penetration of the corona radiata by sperm

• Phase 2- penetration of the zona pellucida by sperm

• Phase 3- fusion of the oocyte and sperm cell Membranes

• Capacitated sperm pass freely through corona cells

FERTILIZATION

• CAPACITATION-modifications of membrane

sterols or surface protins so that spems traverse cumulus oophorus and corona radiata & bind to specific glycoprotein receptors on zona pellucida ZP3 & ZP2

• Acrosomal reaction-interaction of ZP3 with spem head ,fusion of membranes on sperm head releases enzymes ,acrosin ,digest zona around sperm head so enter into perivitelline space

• As sperm enter inside and touches oocyte second meiotic division completes and form female pronuclei

• At same time cortical secretary granules are realesed from plasma membrane of oocyte act on ZP3 to prevent entry of other sperms –zona reaction

uncompacted compacted eight-cell mouse embryos

Day 5

Day 6

implantation

• Posterior wall of uterus,nearer to fundus,may be median plane or to side

• Placenta previa-near internal os

DAY 8

DAY 9

DAY 11- 12

DAY -13

3RD WEEK

• Grastrulation• Primitive streak• Formation of notochord

Formation of notochord

MUSCULOSKELETAL SYSTEM

• 20th day of development –1st somite appear in occipital region

• new somites appear in craniocaudal sequence at a rate of approximately three pairs per until,

• There are 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8 to 10 coccygeal pairs.

• The first occipital and the last five to seven coccygeal somites later disappear, while the remaining somites form the axial skeleton

SOMITE DIFFERENTIATION

• as a ball of mesoderm -then undergo a process of epithelization –

• arrange themselves in a donut shape around a small lumen-

• cells in the ventral and medial walls of the somite lose their epithelial characteristics, become mesenchymal again- surround the neural tube and notochord(sclerotome)-VC & rib.

MYOTOME

• Cells in the dermomyotome ultimately form dermis for the skin of the back and muscles for the back, body wall (intercostal muscles), and some limb muscles

• cells from the ventrolateral edge migrate into the parietal layer of lateral plate mesoderm to form most of the musculature for the body wall (external and internal oblique and transverses abdominis muscles) and most of the limb muscles

FORMATION OF VERTEBRAL COLUMN

RIBA & STERNUM

• Bony potion of rib-sclerotome-grow out from costal processess of thorasic vertebra

• Costal cartilage-sclerotome cells that migrate out into parietal layer of lateral plate mesoderm

• Sternum-parietal layer of lateral plate mesodem

• Cleft sternum

SKULL

• Neurocranium • Viscerocranium• Neurocranium-1.membranous-flat part

2.cartilagenous—base of skull• Membranous-from neural crest cell and

paraaxial mesoderm-mesenchyme-intramembranous ossification-bone spicules-radiate from I centre-apposition growth

• Cartilagenous-rostral to notochord from NCC-prechordal chondrocranium

• From occipital sclerotome-chordal chondrocranoum

• VISCEROCRANIUM-1st 2 pharyngeal arches—maxillalary process,mandibular process

MUSCLE

• Skeletal-paraaxial mesoderm• Smooth-splanchnopleuric mesoderm

surrounding gut tube• Cardiac --splanchnopleuric mesoderm

surrounding heart tube• Head muscle-7 somitomeres• Somitimeres-partially segmented whorls of

mesenchymal cells from paraaxial mesoderm

LIMB DEVELOPMENT

• End of fourth week , limb buds - as outpocketings from the ventrolateral wall

• a mesenchymal core derived from the parietal (somatic) layer of lateral plate mesoderm -form the bones and connective tissues of the limb, covered by a layer of cuboidal ectoderm(apical ectodermal ridge (AER)

Thank you

• Scoliosis-two sucessive vertebrae fuse asymmetrically

• Klippel –feil syndrome• Cleft vertebra(spina bifida)