Gastrulstion And Neurulation Flashcards
Name each part
how does the endoderm form?
FIRST STEP OF GASTRULATION
at the begining of week 3, a node will form on the epiblast layer. (this is known as the primitive streak)
the epiblast cells will divide and flood through this node into the embryo and replace some of the hypoblasts.
This is forming the endoderm.
how is the mesoderm formed?
SECOND STEP OF GASTRULATION
mesoderm forms as the epiblasts spread between the outer most layer of epiblasts and now the inner most layer of epiblasts that have now made the endoderm.
what is the notochord?
it provides both mechanical and signalling cues in the developing embryo.
it will organise the dorsal structures like the spine/ nervous system
what will the notochord release and why?
the notochord will release chordin, noggin and follistatin.
this is so that it blacks BMP in order to get the develoment of the NS.
what are BMP and what do they do?
they are bone morphogenic proteins . this will drive formation of the skin on the back, but the notochord wants to drive neural tissue instead first.
what kind of epithelia will be founf in neuroectoderm?
columnar epithelium
in neural plate
what will the notocord induce?
neurulation
what days will nurulation take place?
20-21
what happens in the first stages on neurulation?
the neural plate (which forms the notocord) converts to a groove then a tube. the cells on the neural plate will thicken forming the folds and a groove.
what happens on day 25/27?
there will be closure at both end of the neural tube
second stage on neurulation?
the folds will fuse to make a tunnel
the neural tube is now formed.
this happens on day 22
2 failures of the neural tube closure?
1- spina bifida
2- anencephaly (you dont get full brain development)
what is the nueral crest?
these are specialised cells that migrate away from the neural tube epithelium
what do neural crest cells do?
they derive from the edges of the neural tube and undergo an epithelial to mesenchymal transition to become mobile and migarate away from the neural tube to widespread destinations.
what are defects in neural crest development?
pigment anomilies, deafness, GI motility issues.
how will mesoderm form in gastrulation?
the epiblast cells will burrow inbetween the epiblast and hypolast to form notocord and the mesoderm.
summary fomration of 3 germ layers.
- cells from the epiblast flow into primative streak
- these cells replace the hypoblast cells to form endoderm
- cells lie between the hypoblast and epiblast form mesoderm
- cells that remain in the epiblast become ectoderm
what are the 3 types of mesoderm
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm
what does paraxial mesoderm become
segmented to form somites
how are somites formed?
they are fomed on the notch clock cycle
- they have an internal timer defined by 90 mins
- a wave of FGF signal passes along the embryo in a rostral caudal direction
- when then FGF wave passes cells, they are programed to change into part of a somite according to where they are in the clock cycle.
what determines wether it is the front or tail end of the somite segemnt that forms?
if the wave passes early in the clock cycle= becomes the front end of that segment
if the wave passes late in the cycle = tail end
homeobox genes function
they direct the formation of body structures at the right place along the body.
derivates of paraxial mesoderm
head and somites
- skelerotome
- Myotome
- Dermatome
derivates of intermediate mesoderm
-kidneys
- urogenital strctures
derivates of lateral plate mesoderm?
- heart
- blood
- spleen
(splanchnic and somatic)
what will the yolk sac become?
the gut tube
endoderm derivates examples
- pancrease
- stomach
- liver
THE GI AND RESP TRACT
ectoderm derivates examples
- epidermis
- nails and teeth
- eyes
- epithelium
- glands
Name each part of the mesoderm
