2nd to 3rd week of embryonic development Flashcards
what happens in the 3rd week of embryo development
1) late gastrulation - migration and invocation
2) development of notochord
3) neural tube and neural crest development
4) folding of embryo
what is a extraembryonic mesoderm
cells of trophoblast rise to a mass of cells that separate the amniotic cavity and primary yolk sac
what is the extraembryonic celom
number of small cavities appear in the extraembryonic mesoderm that later coalesce together
what happen when the extraembryonic celom develops
primary yolk sac becomes smaller and forms a secondary yolk sac
what forms the connecting stalk
extraembryonic celom does not exert into the cranial extraembryonic mesoderm that is between the amnionic cavity and trophoblast
what is the prochordal / prechordal plate
end of embryonic disc, round area becomes thicker than rest of disc
what does the appearance of the prochordal/ prechordal plate determine
- central axis of embryo
- distinguish future head and tail ends
when does the primitive streak develop
beginning of week 3
how doe the primitive streak look
midline at the caudal end of the dorsal aspect of the bilaminar embryonic disc
how does the primative node form
primary streak rises to third layer, elevated cranial end of primary streak from a primitive node
what happens in day 14-15
1) germ disc and primative streak elongates craniocaudally
2) narrow depressed central area of primative streak called primitive groove develops
3) epiblast cells migrate towards primative streak
what is cell migration and specification controlled by
fibroblast growth factor 8 (FGF8) which synthesised by streak cells
what happens to fat cells in late gastrulation
migrate through primative streak towards hypoblast and fill the space between epiblast and hypoblast
what does invagination occur
day 16-17
what happens in invagination
migrating cells invaginate and detach from the primative streak
what is epiblast the source of
all the germ layers
what happen when cells invaginate
some displace the hypoblast creating embryonic endoderm
others lie between epiblast and nearly created endoderm forming mesoderm
how is the trilaminar embryonic disc form
mesoderm –> bilaminar embryonic disc transforms to trilaminar embryonic disk
how is the ectoderm formed
cells remaining in the epiblast
what is the notochord
midline embryonic structure that develops in the 3rd week from the primitive node
what is the axial mesoderm
mesoderm that lies along the central axis and gives rise to the notochord
what are the functions of the notochord
1) forms central axis for developing embryo
2) induces formation of neural tube from overlying ectoderm
3) provides central column which vertebral bodies and intervertebral discs develop
what is the fate of the notochord
- most disappears
- some remain as nucleus pulpous of each intervertebral disc
what is the orophanyngeal membrane
- located in cranial region of primitive streak
- tightly attached ectodermic and endodermic cells
