Embryology 3 - from the blastocyst to neural tube Flashcards
deck complete
where do the cells that make up the adult body come from
the inner cell mass
what does the layer of inner cell mass facing fluid become
the hypoblast
what is formed after the hypoblast
the epiblast
what two cavities are initially created
the yolk sac and the amniotic sac
where do cells separate in monozygotic twinning
inside the zona pellucida
what is formed from the 2-cell stage zygote in monozygotic twinning
two inner cell masses within a single blastocyst cavity
what do monozygotic twins share during pregnancy
common chorionic cavity and common placenta
what is there a danger of with monozygotic twins
foetal transfusion syndrome/’twin to twin’ transfusion syndrome
what do the cells at the centre of the hypoblast make
hex
where do hex-expressing cells move
to rim of embryo, congregate at one point
what do hex-expressing cells secrete
proteins that inhibit progress in epiblast layer above hypoblast
what is special about cells on opposite side of embryo to hex-expressing cells
far enough to escape progress inhibition. can begin making tail end of primitive streak
where does the primitive streak extend to
in direction of hex-expressing cells, to middle of epiblast
what is formed at the end of the primitive streak in the centre of the epiblast
the node
what is formed at the primitive streak end of the embryo
the future trunk
what is formed at the non primitive streak end of the embryo
the future head
what does the formation of one body axis depend on
the hex-expressing cells being in one point on the rim of the hypoblast
what will happen if 2 distinct sites are formed
two heads will form and potentially 2 primitive streaks - nothing separates the two embryos
what results in conjoined twins
when 2 head organising areas still agree on one site for the tail - i.e. two heads, one tail
in simple terms, what are humans/what do they start as
three layered disc
outer skin - ectoderm
middle layer, muscle etc - mesoderm
inner layer - endoderm (gut)
what is the process called when the ‘flat disc’ of the epiblast turns into a 3-layered structure
gastrulation
how does the endoderm form
from cells diving through streak
what does the middle part of the endoderm rise to form
notochord plate
what does the notochord plate detach to form
the notocord
where does the central nervous system tube derive from
the ectoderm
when does CNS formation begin
when the ectoderm along the dorsal surface folds inwards, driven by local cell shape changes along three stripes - 2 edge and 1 central
what happens as the tissue forming the CNS folds
tissue folds inwards due to cell proliferation - helps bring edges together. forms a sealed ectoderm and a neural tube
what happens when the sealing of the edges of the tube and its separation from the ectoderm fails
the inside of the spinal cord or brain is exposed - spina bifida or anencephaly
what is anencephaly
where the inside of the brain is open to the back of the head - stops the brain growth so the upper-back head is effectively missing. incompatible with post-natal life
