Gastrulation

Question 1

What is gastrulation?

Answer 1

• a process where a single layer gives rise to 3 distinct layers

Question 2

What three germ layers do vertebrates have?

Answer 2

• ectoderm - outer layer
• mesoderm - middle layer
• endoderm - inner layer

Question 3

What part of the blastula embryo is responsible for gastrulation?

Answer 3

• the epiblast is responsible for forming all 3 germ layers

Question 4

What are the two layers of the blastula embryo? And describe these

Answer 4

• epiblast = 1 cell thick and gives rose to all 3 germ layers
• hypoblast = 1 cell thick and makes no contribution to the germ layers

Question 5

What layers develop from the epiblast?

Answer 5

• Mesoderm
• Endoderm

Question 6

What cell remain in the epiblast?

Answer 6

• Ectoderm

Question 7

How does the blastula form a gastrula

Answer 7

1. cells in the middle layer of epiblast converge to the middle of disc = from the primitive streak
2. this begins at the posterior end and extends to the anterior end
3. cells don’t pile up on top but ingress as individual cells
4. cells continually keep moving from the edges towards the midline and ingress

Question 8

How does the endoderm form from the epiblast?

Answer 8

• 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

Question 9

How is the mesoderm formed from the epiblast?

Answer 9

• 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

Question 10

What is the node and how is it formed?

Answer 10

• 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

Question 11

What happens to epiblast cells that ingress through the node?

Answer 11

• epiblast cells that ingress through the node migrate anteriorly to from the structures of the head

Question 12

What is the regressing node?

Answer 12

• regressing node formed as the node at the end of the primitive streak starts to regress posteriorly

Question 13

What is the definition of primary gastrulation?

Answer 13

• 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

Question 13

What happens to cells that ingress through the regressing node?

Answer 13

• 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

Question 14

What is the tailbud?

Answer 14

• the tail bud is a knot of stem cells in the posterior of the streak
• the tailbud moves posteriorly leaving behind cells

Question 15

What is secondary gastrulation?

Answer 15

Secondary gastrulation is gastrulation through the tailbud
- forms mesoderm cells of posterior notochord and somites

Question 16

What does the ectoderm form?

Answer 16

• all neural tissue, epidermis, neural crest

Question 17

What does the mesoderm form?

Answer 17

• muscle, bone, organs

Question 18

What does the endoderm form?

Answer 18

• lining of the gut and derivatives