Developing Embryo

Question 1

How is the hypoblast formed?

Answer 1

Layer of the inner cell mass facing fluid becomes hypoblast (internal differences)

Question 2

What does the hypoblast eventually form?

Answer 2

The yolk sac (cavity within the embryo)

Question 3

What is the epiblast?

Answer 3

The layer of cells in the inner cell mass that is in direct contact with the hypoblast, forming the amniotic sac

Question 4

What has the embryo achieved by creating the epiblast and hypoblast?

Answer 4

1. Become multicellular
2. Created differences
3. Used the differences to create two sacs and beginning of placenta

Question 5

Describe the three ways in which monozygotic twins can be formed?

Answer 5

1. Cells separate within zona pellucida after cleavage
2. Two inner cell masses form (share placenta)- twin to twin transfusion syndrome
3. Two primitive streaks form- common amniotic cavity/ conjoined twins

Question 6

How does the 2D disc transform into 3 coordinates?

Answer 6

Radial properties- cells at the centre of the hypoblast produce protein Hex, Hex-expressing cells move to the rim to congregate at one point

Question 7

How is the primitive streak formed?

Answer 7

Hex-expressing cells secrete proteins that inhibit progress in epiblast layer above so cells far enough away from inhibition make tail end of primitive streak

Question 8

How is the node formed?

Answer 8

The primitive streak extends and forms a node. Primitive streak end- future trunk

Question 9

What is the name of the process of an epiblast turning into a 3D structure?

Answer 9

Gastrulation

Question 10

What are the three cylinders?

Answer 10

Ectoderm- outer skin
Mesoderm- middle/muscle layer
Endoderm- inner skin/ gut

Question 11

How is the mesoderm layer formed?

Answer 11

Many epiblast cells converge on streak and dive through, some cells spread out between discs to make mesoderm

Question 12

How is the endoderm layer formed?

Answer 12

Many epiblast cells converge on streak and dive through, some cells push the hypoblast aside to make the endoderm

Question 13

How is the notochord formed?

Answer 13

The middle part of the new endoderm rises to make the notochord plate then detaches to form the notochord (runs down trunk of embryo)

Question 14

How does the endoderm become a tube?

Answer 14

The embryo lengthens so ends of the endoderm folds into tubes due to the constraints of the yolk sac (digestive tract)