Miscellaneous folding of the embryo; origins of body wall layers, primitive gut, mesenteries, and umbilicus

Question 1

Consequences of the head fold (7)

OP membrane?
Foregut?
Where are heart tubes?
Where is septum transversum?
What happens to the rostral neuropore?
Where is ectoderm now?
Where is amniotic cavity?

Answer 1

1. OP membrane now ventral to the brain
2. Foregut is formed
3. Heart tubes are now dorsal to the IEC (originally ventral)
4. Heart tubes now ventral to the brain and gut
5. Septum transversum is now caudal to the heart
6. Rostral neuropore closes
7. Ectoderm covers rostral part of the embryo, while amniotic cavity surrounds the rostral part of the embryo

Question 2

Consequences of the tail fold (7)

Where is the cloacal membrane?
Hindgut?
Cloaca?
Connecting stalk is where?
Allantois is where?
What happens to caudal neuropore?
Where is ectoderm? Where is amniotic cavity?

Answer 2

1. Cloacal membrane (-> anus) is ventral to spinal cord
2. Hindgut has formed from caudal portion of yolk sac
3. Cloaca has formed (tailgut) -> rectum and urinary bladder
4. Connecting stalk swings ventrally
5. Allantois is also now ventral
6. Caudal neuropore closes
7. Ectoderm covers the caudal end of the embryo and the amniotic cavity surrounds the caudal end of the embryo

Question 3

Define somatopleure

Answer 3

the body layer formed by ectoderm plus somatic mesoderm from lateral plate

Question 4

Define splanchnopleure

Answer 4

the body layer formed by endoderm plus splanchnic mesoderm from lateral plate

Question 5

What are the contents of the umbilicus?

Answer 5

EEM, connecting stalk
allantois
umbilical vessels (2 arteries, 1 vein)
yolk stalk surrounded by residual opening to IEC
umbilical cord is wrapped by amniotic membrane

Question 6

What happens to the chorion/chorionic cavity?

Answer 6

The amnion expands and takes it over/absorbs it

Question 7

What are the results of the transverse fold?

Answer 7

1. midgut formed
2. ectoderm covers the ventral surface of the embryo except at the umbilical ring
3. amniotic cavity surrounds the ventral surface of the embryo except at the umbilical ring
4. definitive umbilicus/umbilical cord has now formed (but we still have a ways to go in closure of the ventral body wall)

Question 8

What is gastroschisis?

Answer 8

a failure in the ventral body wall closure