Much of this conditioning during capacitation occurs in the uterine tube and involves epithelial interactions between the sperm and the mucosal surface of the tube. During this time, a glycoprotein coat and seminal plasma proteins are removed from the plasma membrane that overlies the acrosomal region of the spermatozoa.Only capacitated sperm can pass through the corona cells and undergo the acrosome reaction
Spermatozoa are not ableto fertilize the oocyte immediately upon arrivalin the female genital tract but must undergo(1) capacitation and (2) the acrosome reactionto acquire this capability.Capacitation is a period of conditioning inthe female reproductive tract that in the humanlasts approximately 7 hours
After fertilization clevage –first divisionTill 8 cell stage cells are loosely arrangedCompaction-inner cell mass-embryo outer cell mass –trophoblast16 cell stage morula day 3,day 4-enters uterine cavity,cavity appears inside morulaEmbyonic pole
Cavity-primary yolk sac ,primary umbilical vesocleAs secondary yolk sac is forming diverticulum of visceral hypoblast, an allantois,extend into extraembryonicmesoblast.Exrtraembryonicmesoblast-do not contribute to future body directlyCovers amnion ,II yolk sac ,internal wall of mural trophoblast,form connecting stalk
by apposition of newlayers on the outer surface and by simultaneousosteoclasticresorption from the inside.
The base of the skull is formed whenthese cartilages fuse and ossify by endochondralossification (Figs. 10.3 and 10.6).
The bone-forming capacity of mesenchymeis not restricted to cells of the sclerotome,but occurs also in the parietal layer ofthe lateral plate mesoderm of the body wall.
lateral plate mesoderm of the body wall.This layer of mesoderm forms bones of thepelvic and shoulder girdles, limbs, and sternum
Resegmentation occurs when the caudal halfof each sclerotome grows into and fuses withthe cephalic half of each subjacent sclerotome
wall (rectus abdominus, internal and externaloblique, and transversusabdominus), and limbmuscles. The remaining cells in the myotomeform muscles of the back, shoulder girdle,and intercostal muscles
10 general embryology & musculoskeletal system 13:05
DEVELOPMENT OFMUSCULOSKELETAL SYSTEM WITHGENERAL EMBRYOLOGYDR KIRTI S SOLANKE
stages• 23 stages-first 8 weeks after ovulation• Streeter(1942) and ORahilly & Müller (1987).• Comparing with other embryos
Primordial germ cell formation• Gamets –PGC-formed in epiblast during 2nd wkof dev move to wall of yolk sac• 4th wk migrate from yolk sac-arrive in devgonad at 5th wk• For preparation of fertilization ,has to undergogametogenesis-meiosis-to redusechromosome no cytodifferentiation-tocomplete maturation
THE PHASES OF FERTILIZATIONINCLUDE• Phase 1- penetration of the corona radiata bysperm• Phase 2- penetration of the zona pellucida bysperm• Phase 3- fusion of the oocyte and sperm cellMembranes• Capacitated sperm pass freely through coronacells
FERTILIZATION• CAPACITATION-modifications of membranesterols or surface protins so that spemstraverse cumulus oophorus and corona radiata& bind to specific glycoprotein receptors onzona pellucida ZP3 & ZP2
• Acrosomal reaction-interaction of ZP3 withspem head ,fusion of membranes on spermhead releases enzymes ,acrosin ,digest zonaaround sperm head so enter into perivitellinespace• As sperm enter inside and touches oocytesecond meiotic division completes and formfemale pronuclei• At same time cortical secretary granules arerealesed from plasma membrane of oocyteact on ZP3 to prevent entry of other sperms –zona reaction
• 20th day of development –1st somite appearin occipital region• new somites appear in craniocaudal sequenceat a rate of approximately three pairs peruntil,• There are 4 occipital, 8 cervical, 12 thoracic, 5lumbar, 5 sacral, and 8 to 10 coccygeal pairs.• The first occipital and the last five to sevencoccygeal somites later disappear, while theremaining somites form the axial skeleton
SOMITE DIFFERENTIATION• as a ball of mesoderm -then undergo aprocess of epithelization –• arrange themselves in a donut shape around asmall lumen-• cells in the ventral and medial walls of thesomite lose their epithelial characteristics,become mesenchymal again- surround theneural tube and notochord(sclerotome)-VC &rib.
MYOTOME• Cells in the dermomyotome ultimately formdermis for the skin of the back and muscles forthe back, body wall (intercostal muscles), andsome limb muscles• cells from the ventrolateral edge migrate into theparietal layer of lateral plate mesoderm to formmost of the musculature for the body wall(external and internal oblique and transversesabdominis muscles) and most of the limb muscles
RIBA & STERNUM• Bony potion of rib-sclerotome-grow out fromcostal processess of thorasic vertebra• Costal cartilage-sclerotome cells that migrateout into parietal layer of lateral platemesoderm• Sternum-parietal layer of lateral platemesodem• Cleft sternum
SKULL• Neurocranium• Viscerocranium• Neurocranium-1.membranous-flat part2.cartilagenous—base of skull• Membranous-from neural crest cell andparaaxial mesoderm-mesenchyme-intramembranous ossification-bone spicules-radiate from I centre-apposition growth
• Cartilagenous-rostral to notochord from NCC-prechordal chondrocranium• From occipital sclerotome-chordalchondrocranoum• VISCEROCRANIUM-1st 2 pharyngeal arches—maxillalary process,mandibular process
MUSCLE• Skeletal-paraaxial mesoderm• Smooth-splanchnopleuric mesodermsurrounding gut tube• Cardiac --splanchnopleuric mesodermsurrounding heart tube• Head muscle-7 somitomeres• Somitimeres-partially segmented whorls ofmesenchymal cells from paraaxial mesoderm
LIMB DEVELOPMENT• End of fourth week , limb buds - as outpocketingsfrom the ventrolateral wall• a mesenchymal core derived from the parietal(somatic) layer of lateral plate mesoderm -form thebones and connective tissues of the limb, coveredby a layer of cuboidal ectoderm(apical ectodermalridge (AER)