Development Of GI and lungs

Question 1

How is the primitive gut tube formed?

Answer 1

Amnion folds around embryo (cranial to caudal, and laterally) pinching part of the yolk sac (formed by endoderm) to form the primitive gut tube

Question 2

What is the connection between the yolk sac and the primitive gut tube called?

Answer 2

Vitelline duct

Question 3

How is the body cavity formed?

Answer 3

The anterior edges of the amnion fuse to cover the embryo on all sides

Question 4

What is the intraembryonic coelomic cavity?

Answer 4

Cavity surrounding the primitive gut tube formed by the somatopleuric mesoderm (body wall) and splanchnopleuric mesoderm (around gut tube)

Question 5

What suspends the primitive gut tube from the dorsal body wall?

Answer 5

The dorsal mesentery

Question 6

What structure separates the peritoneal and pleural cavities?

Answer 6

Septum transversum

Question 7

Where are cells of the septum transversum found before they separate the two body cavities?

Answer 7

Cranial to the cardiogenic area - cranial/caudal folding brings it to its more caudal positioning

Question 8

What do hox genes do? How do they influence gut formation? Where do they come from?

Answer 8

Pattern the embryo

Different Hox gene expression determines the type of gut formed

Cells of the splanchnopleuric mesoderm

Question 9

From what do the trachea and lungs form?

Answer 9

A midline lung bud from the endodermal foregut, caudal to the pharyngeal arches

Question 10

Which transcription factor initiates lung bud formation?

What is the main factor for outgrowth? Name for type of growth in lung buds?

Answer 10

Initiates = Nkx2.1
Outgrowth = FGF10 - branching morphogenesis

Question 11

What is an esophagotracheal fistula?

Answer 11

Where the upper esophagus is a blind ending duct and the distal esophagus is connected to the trachea

Question 12

What other mesentery (not dorsal mesentery) is present to anchor the primitive gut? What two structures does it form and where?

Answer 12

Ventral mesentery
— between liver and stomach = lesser omentum
— between liver and anterior body wall = falciform ligament

Question 13

When and how does the stomach form?

Answer 13

week 4

Differential growth causes 2 rotations:

1 — left side moves anteriorly (forming greater and left curvatures)
2 — pylorus moves to the right

Question 14

What induces liver formation? What forms and when?

Answer 14

FGF signalling from cardiac mesoderm induces growth of hepatic diverticulum during week 4

Question 15

When does first rotation of the midgut occur? Around which axis and by how much in which direction?

Answer 15

Week 6 -around the superior mesenteric artery from the vitelline duct by 90 degrees anti-clockwise

Question 16

What causes the second rotation of midgut and by how much? During which weeks does this take place?

Answer 16

Retraction of the herniated midgut back into the abdominal cavity which is now large enough for it to fit - by 180 degrees anticlockwise

10th-12th week

Question 17

What microstructures cause the rotation?

Answer 17

Nodal cilia that create asymmetric gene transcription patterns

Question 18

What is the common opening of the gut and the urogenital system called?
What partitions them?

Answer 18

Cloaca

Urorectal septum separates

Question 19

Which cells are the cells of the enteric nervous system derived from?

Answer 19

Neural crest cells

Question 20

What direction do the enteric nerves migrate?

Answer 20

Cranial to caudal

Question 21

Hirschsprung’s Disease? Cause?

Answer 21

Failure of neural crest migration so absence of enteric nervous system
Largely affects distal colon, removing its ability to remove stool

Mutations in ligand (GDNF) or receptor (c-ret) that promote survival and proliferation of the enteric nervous system

Question 22

What is the primary intestinal loop formed by?

Answer 22

Ileum grows quicker than abdominal cavity can accommodate so it loops and herniates into the vitelline duct