Early Development Flashcards
Zygote
diploid. under go rapid mitotic divisions (cleavage divisions)
Stages of pre embryonic period
zygote, morula, blastocyst
Morula
solid ball of 16-32 cells called blastomeres
Blastocyst features:
- fluid filled cavity (blastocoel)
- inner cell mass
- trophoblast
Inner cell mass
cells will divide and differentiate to form the embryo
Trophoblast
cells will divide and differentiate to form chorion
Chorion
derived from trophoblast cells. provides nutrients to developing embryo
Implantation
blastocyst moves from uterine tube and attaches to endometrium of uterine wall
After implantation inner cell mass forms a..
1-layered (bilayered) embryonic disc
Embryonic disc is composed of:
Epiblast and hypoblast
Epiblast undergoes mitosis to form:
- amnion (fluid filled amniotic cavity)
- 3 germ layers of the embryo
Hypoblast undergoes mitosis to form:
yolk sac
3 germs layers forming embryo
ectoderm, mesoderm, endoderm
Ectoderm
(top) will form the nervous system and the epidermis of the skin
Mesoderm
(middle)will form muscles, cardiovascular system, dermis, and most bones
Endoderm
will form epithelial linings of digestive, respiratory, urinary and reproductive systems and their associated glands
During embryonic period what happens
- major organ systems almost completely formed
- heart begins to beat
- limb buds differentiate
- embryonic membranes form
Embryonic membranes
Chorion, amnion, yolk sac, allantois
Amnion
derived from epiblast. forms amniotic cavity which surrounds embryo/fetus with amnion fluid
Yolk sac
derived from hypoblast. forms part of gut, produces earliest blood cells, source of reproductive cells
Allantois
out pocket of yolk sac, forms umbilical cord and urinary bladder
