Embryology 3 - from the blastocyst to neural tube

Question 1

where do the cells that make up the adult body come from

Answer 1

the inner cell mass

Question 2

what does the layer of inner cell mass facing fluid become

Answer 2

the hypoblast

Question 3

what is formed after the hypoblast

Answer 3

the epiblast

Question 4

what two cavities are initially created

Answer 4

the yolk sac and the amniotic sac

Question 5

where do cells separate in monozygotic twinning

Answer 5

inside the zona pellucida

Question 6

what is formed from the 2-cell stage zygote in monozygotic twinning

Answer 6

two inner cell masses within a single blastocyst cavity

Question 7

what do monozygotic twins share during pregnancy

Answer 7

common chorionic cavity and common placenta

Question 8

what is there a danger of with monozygotic twins

Answer 8

foetal transfusion syndrome/’twin to twin’ transfusion syndrome

Question 9

what do the cells at the centre of the hypoblast make

Answer 9

hex

Question 10

where do hex-expressing cells move

Answer 10

to rim of embryo, congregate at one point

Question 11

what do hex-expressing cells secrete

Answer 11

proteins that inhibit progress in epiblast layer above hypoblast

Question 12

what is special about cells on opposite side of embryo to hex-expressing cells

Answer 12

far enough to escape progress inhibition. can begin making tail end of primitive streak

Question 13

where does the primitive streak extend to

Answer 13

in direction of hex-expressing cells, to middle of epiblast

Question 14

what is formed at the end of the primitive streak in the centre of the epiblast

Answer 14

the node

Question 15

what is formed at the primitive streak end of the embryo

Answer 15

the future trunk

Question 16

what is formed at the non primitive streak end of the embryo

Answer 16

the future head

Question 17

what does the formation of one body axis depend on

Answer 17

the hex-expressing cells being in one point on the rim of the hypoblast

Question 18

what will happen if 2 distinct sites are formed

Answer 18

two heads will form and potentially 2 primitive streaks - nothing separates the two embryos

Question 19

what results in conjoined twins

Answer 19

when 2 head organising areas still agree on one site for the tail - i.e. two heads, one tail

Question 20

in simple terms, what are humans/what do they start as

Answer 20

three layered disc
outer skin - ectoderm
middle layer, muscle etc - mesoderm
inner layer - endoderm (gut)

Question 21

what is the process called when the ‘flat disc’ of the epiblast turns into a 3-layered structure

Answer 21

gastrulation

Question 22

how does the endoderm form

Answer 22

from cells diving through streak

Question 23

what does the middle part of the endoderm rise to form

Answer 23

notochord plate

Question 24

what does the notochord plate detach to form

Answer 24

the notocord

Question 25

where does the central nervous system tube derive from

Answer 25

the ectoderm

Question 26

when does CNS formation begin

Answer 26

when the ectoderm along the dorsal surface folds inwards, driven by local cell shape changes along three stripes - 2 edge and 1 central

Question 27

what happens as the tissue forming the CNS folds

Answer 27

tissue folds inwards due to cell proliferation - helps bring edges together. forms a sealed ectoderm and a neural tube

Question 28

what happens when the sealing of the edges of the tube and its separation from the ectoderm fails

Answer 28

the inside of the spinal cord or brain is exposed - spina bifida or anencephaly

Question 29

what is anencephaly

Answer 29

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