4. 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
5. 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
6. 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
7. • 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
28. • 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
29. 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.
30.
31. 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
33. 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
34. 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
35. • Cartilagenous-rostral to notochord from NCC-
prechordal chondrocranium
• From occipital sclerotome-chordal
chondrocranoum
• VISCEROCRANIUM-1st 2 pharyngeal arches—
maxillalary process,mandibular process
36.
37. 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
38.
39. 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)
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).
Skull ,sternum,vertcolum,ribs
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