Unit 3: Gastrulation Flashcards
Define gastrulation
A process where a single layer gives rise to 3 distinct layers
What 3 germ layers do vertebrates have ?
1) Ectoderm
2) Mesoderm
3) Endoderm
What is the ectoderm ?
The outside layer
What is the mesoderm ?
The middle layer
What is the endoderm ?
The inner layer
How many layers does the blastula embryo have and what are they ?
2 layers
- Epiblast
- Hypoblast
Does the epiblast give rise to any germ layers, if so how many ?
Epiblast gives rise to all 3 germ layers
Does the hypoblast give rise to any germ layers, if so how many ?
Hypoblast does not contribute to germ layers
How does the blastula form a gastrula (2) ?
- 2 New layers develop from the epiblast (Mesoderm and Endoderm)
- Cells remaining in epiblast become ectoderm
How is the primitive streak formed (3) ?
- Cells in the middle of the epiblast converge to the middle of the disk
- Epiblast cells ingress as individual cells
- Moving from the edge to the midline
What are the first cells to ingress ?
Endoderm cells
How is the endoderm formed ?
- Posterior cells drop down to contact the hypoblast
- This forms a sheet of cells
What are the second cells to ingress ?
Mesoderm cells
How is the mesoderm formed ?
- Mostly anterior cells sit between the epiblast and endoderm
- Cells have to undergo EMT
How is the primitive streak formed ?
- Cells found in the middle of the epiblast
- Undergo EMT
- Ingress (go under) and then undergo MET
- ‘Gap’ in the middle forms
What is the node ?
Knot of diving stem cells
How is the node formed ?
- Cells condense at the anterior end of streak to form the node
- Epiblast cells that ingress through the node migrate anteriorly to form parts of the head
When the node starts progressing posteriorly, what cell type does it leave behind and what does this form ?
- Leaves behind mesoderm cells
- This forms the notochord and somites
What is the tailbud ?
A knot of stem cells in the posterior of the streak
What is primary gastrulation ?
Formation of primitive streak and hensens node
Describe the steps of secondary gastrulation (3)
1) The tailbud moves posteriorly leaving cells behind
2) This forms mesoderm cells of the posterior notochord and somites
3) It never forms endoderm
