1
Fertilization & Implantation
Topics for today:
• Blastula and implantation• Formation of chorion• Gastrula & Tissue differentiation• Neurula and organogenesis• Limb bud stage
Implantation
day 7endometriumovulation
morula
blastula
fertilization
mitosis
Chorion formation & releaseof chorionic gonadotropin
2
Early Embryo Stages
Zygote morula blastula ovum
spermatozoan
cleavagefertilization0 d 3 d
stage atimplantation
5 dblastulation
Undifferentiated embryo stem cells
Mid to Late Embryo Stages
blastula gastrula neurula18 d 8 d
gastrulation
Undifferentiated inner cell mass
neurulation
blastula gastrula
Inner cell mass splits to 2 layers(differentiation begins)
gastrocoele
day 7 day 8-9
Chorion formation &release of HCG
releases HCG
day 7
Beginning formation of chorion,first layer of developing placenta
Chorion releases chorionicgonadotropin (HCG), a hormonewhich tells corpus luteum tocontinue release of progesterone
Progesterone is essential formaintenance of placenta
3
Extra embryonic membranesMembranes that support development
of embryo proper
• Chorion - outermost; 1st to appear
• Amnion - contains amnionic fluid; 2nd
• Yolk Sac - gives rise to gut; 3rd
• Amnion - bladder precursor; last
Gastrulation...beginning of tissue development
day 10
amnion
early ectoderm
early endoderm
chorion
Late gastrula stageMesoderm
forming
day 12
4
Neurula stage of developmentNeurula Neurula stage of developmentstage of development
Brainregion
Spinal cordregion
About 2 weeks old
Dorsal view showingdeveloping nerve cord
Developing somites(body segments) visible
Period of extensive organ development
SEM view of neurula stage(transverse view of neural tube)
neural tube
notochord
dorsal aortae
gut
About 3 wks
Formation of yolk sac
Week 3-4
5
Brainregion
Limbbuds
Jaws
Late embryo with limb buds
Eye
Heart
About 4 wks
Late embryo & the placenta
Topic for Wednesday:
Fetus and Parturition