Life before birth Flashcards
What are the 3 early developement stages before birth
Preimplantation, embryonic and foetal stage
What week does preimplantation occur
week 1
What weeks do embrhyonic stage occur
week 2-8
What weeks do foetal stages occur
week 9-38
Describe cleavage
mitotic division of fertilised oocyte, which allow passage down the narrowest part of the uterine tube. oocyte Is surrounded by tough glycoprotein coat to prevent embryo from implanting
Describe Blatocyte formation
ormed from morula. 2 population in blastocyst. Inner cell mass forms the embryo. The outside cells (trophectoderm) form placental structure. Differentiation occurs – inner cell mass form embryo and extraembryonic tissue. Outer cells form trophoblast (part of placenta)
Define gastrulation
The process of • Cell division and the migration of these dividing cells. Results in the formation of 3 germ layers.
Describe the formation of the germ layers
Oncde cells have invaginated. some displace the hypoblast creating the endoderm. Others lie between the epiblast and endoderm to form mesoderm. Remaining cells in the epiblast form the ectoderm
What does ectoderm go on to form
nervous system, tooth enamel, cornea and eye lens
What does endoderm go on to form
Liver, pancreas and thymus
What does mesoderm go on to form
Notochord, dermis, skeletal system
Name the 3 extra embryonic membranes
Amnion, yolk sac and chorion
What is the yolk ac continuous with
The hypoblast
When does the yolk sac dissapear
week 20
What is the yolk sac involved in
Nutrient tranfer in early weeks
