Gastrulation Flashcards
What is gastrulation?
- a process where a single layer gives rise to 3 distinct layers
What three germ layers do vertebrates have?
- ectoderm - outer layer
- mesoderm - middle layer
- endoderm - inner layer
What part of the blastula embryo is responsible for gastrulation?
- the epiblast is responsible for forming all 3 germ layers
What are the two layers of the blastula embryo? And describe these
- epiblast = 1 cell thick and gives rose to all 3 germ layers
- hypoblast = 1 cell thick and makes no contribution to the germ layers
What layers develop from the epiblast?
- Mesoderm
- Endoderm
What cell remain in the epiblast?
- Ectoderm
How does the blastula form a gastrula
- cells in the middle layer of epiblast converge to the middle of disc = from the primitive streak
- this begins at the posterior end and extends to the anterior end
- cells don’t pile up on top but ingress as individual cells
- cells continually keep moving from the edges towards the midline and ingress
How does the endoderm form from the epiblast?
- formed from the posterior cells that ingress through the primitive streak
- the cells drop down to contact the hypoblast and then form a sheet of cells, the endoderm
How is the mesoderm formed from the epiblast?
- formed from the next lot of cells (more anterior) that ingress through the primitive streak
- these cells form a mass of cells between the endoderm and the epiblast
What is the node and how is it formed?
- primitive streak elongation stops about 75% length of the axis
- the node is a knot of dividing stem cells formed as cells condense at the anterior end of the primitive streak
What happens to epiblast cells that ingress through the node?
- epiblast cells that ingress through the node migrate anteriorly to from the structures of the head
What is the regressing node?
- regressing node formed as the node at the end of the primitive streak starts to regress posteriorly
What is the definition of primary gastrulation?
- primary gastrulation is gastrulation through the primitive streak and node
- it accounts for tissues of the head and body to hindlimb level
- the node runs out of stem cells at the level of the hindlimb
What happens to cells that ingress through the regressing node?
- cells that ingress through the regressing node are pushed down into the mesoderm layer
- cells that gastrulate though the regressing node only ever form mesoderm cell that go on to from the notochord and somite’s
What is the tailbud?
- the tail bud is a knot of stem cells in the posterior of the streak
- the tailbud moves posteriorly leaving behind cells
What is secondary gastrulation?
Secondary gastrulation is gastrulation through the tailbud
- forms mesoderm cells of posterior notochord and somites
What does the ectoderm form?
- all neural tissue, epidermis, neural crest
What does the mesoderm form?
- muscle, bone, organs
What does the endoderm form?
- lining of the gut and derivatives