3rd week of development- trilaminar germ disc Flashcards
most characteristic event happening in 3rd week and what happens in it
gastrulation
establishment of 3 germ layers
gasturlation begins with
the formation of primitive streak within the epiblast
primitive node is where
caudal end of primitive streak has a primitive pith with elevations on side
cells migrate into the primitive streak, so upon the arrival they become what and what happens
they become flask shaped and detach from the epiblast
cell migration and specification is controlled by
fibroblast growth factor 8
what binds epiblast cells together
E-cadherin which is down regulated by FGF-8
cell specification into mesoderm is regulated by
BRACHYURY (T) expression
on the cephalic direction they come in contact with
prechordal plate
prechordal plate is made where
between the tip of the notochord and the oropharyngeal membrane
prechordal plate is important
induction of forebrain
where oral cavity is made
oropharyngeal membrane at the cranial end of the disk has a small region of tightly adherent ectoderm and endoderm that represent future opening of the oral cavity
formation of notochord
the pronotochordal cells invaginate into the primitive streak cranially until they reach prechordal plate and get intercalated with the hypoblast so for time being the embryo has 2 layers of cells that make up the notochord plate
the cells of notochord plate proliferate and detached from epiblast to form a definitive notochord (because the hypoblast cells are getting replaced by endodermal cells)
neurenteric canal
primitive pith makes an indentation in the epiblast which temporarly connect the yolk sac and amnion
cloacal membrane is made where and what does it do
its made at the caudal end of the embryonic plate
when the coacal membrane appears the posterior wall of yolk sac forms a diverticulum which is called as allantoenteric diverticulum or allontois which appears on 16th day
allontois in humans
remains rudimentary and can be involved in the making abnormalities of bladder development
explain the formation of secondary villi
mesodermal cells penetarte into the primary villi and grow towards the decidua and make secondary villi
explain formation of tertiary villi
the mesodermal cells differentiate into blood cells and vessels forming the villous capillary system which is called the tertiry villi aur definitive placental villus
how the embryo is given the oxygen and nutrients
the tertiary villi capillaries make contact with the capiliaries in the mesoderm of of chorionic plate and in connecting stalk
which make contact with intramebryonic circulatory system and connects the embryo with placenta so when in the 4th week of development the heart starts beating the embryo is givng nutrients etc
outer trophoblast shell
the cytotrophoblast penetrate and poliferate into the surrounding syncytium until they reach the maternal endometrium and make connections with the neighbouring villous extension stems and make the outer trophoblast shell
where the placenta is made
the part of villi that extends from the chorionic plate into the decidual plate in the endometrium and thats where placenta is made
