Development of the Gastrointestinal Tract: Foregut

Question 1

What forms the superior and inferior boundaries of the primitive gut tube?

Answer 1

Superior: oropharangeal membrane Inferior: cloacal membrane

Question 2

At what point is the midgut continuous with the yolk sac?

Answer 2

The vitelline duct.

Question 3

What structure present in 2% of people is a remnant of the vitelline duct.

Answer 3

Meckel’s diverticulum.

Question 4

From which germ layer the epithelial lining of the gut tube derived?

Answer 4

Endoderm

Question 5

From which germ layer is the smooth muscle and connective tissue derived?

Answer 5

Visceral mesoderm.

Question 6

Which germ layers give rise to the visceral and parietal peritoneum?

Answer 6

Visceral and parietal mesoderm.

Question 7

What structure suspends the primitive gut tube from the posterior abdominal wall.

Answer 7

Dorsal mesentery.

Question 8

What are the boundaries of the dorsal mesentery?

Answer 8

Lower oesophagus to cloaca.

Question 9

What are the boundaries of the ventral mesentery?

Answer 9

Lower oesophagus to 1st part of the duodenum.

Question 10

Into what does the dorsal mesentery develop?

Answer 10

The greater omentum and mesocolon.

Question 11

Into what does the ventral mesentery develop?

Answer 11

Lesser omentum and falciform ligament (umbilical vein).

Question 12

Into what do the vitelline arteries develop?

Answer 12

Coeliac trunk - foregut. Superior mesenteric - midgut. Inferior midgut - hindgut.

Question 13

Describe the development of the gut tube endoderm.

Answer 13

1. Week six - proliferation of the endoderm occludes the hollow gut tube.
2. Apoptosis of the epithelium occurs over the next 2 weeks creating vacuoles - recanalisation
3. Vacuoles coalesce to fully recanalise the gut tube by week 9.

During this process the epithelium lining undergoes further differentiation

Question 14

Which developmental abnormalities arise from abnormal recanalisation of the gut tube?

Answer 14

Duplication, atresia, stenosis.

Question 15

What are the superior and inferior boundaries of the foregut?

Answer 15

Superior - oropharyngeal membrane.

Inferior - first part of the duodenum.

Question 16

What (non-GI) structure does the foregut also give rise to?

Answer 16

The respiratory diverticulum.

Question 17

What structure grows to seperate the trachea from the lowe pharynx?

Answer 17

Tracheoesophageal septum

Question 18

Which foetal abnormality results from a displacement of the trancheoesophageal septum?

Answer 18

Oesophageal atresia - prevents the foetus swallowing amniotic fluid and returning it to the mother through the placental circulation. Polyhydramnios results.

Question 19

What is the survival rate from oesopahgeal atresia following surgical repair?

Answer 19

85%

Question 20

In what week does the oesophagus from?

Answer 20

Week 4.

Question 21

What feature does the oesophagus have that is not found in the rest of the gut tube?

Answer 21

Skeletal muscle derived from paraxial mesoderm.

Question 22

What is the aetieology of a congenital hiatal hernia and what feature makes it different to an adult aquired hiatal hernia?

Answer 22

Oesophagus lengthens rapidly in weeks 4-7 as stomach descends. Insufficient elogation results in part of the stomach positioned supradiaphagmatically. Is irreducible, unlike acquired.

Question 23

In what week of development does the stomach appear?

Answer 23

4

Question 24

Which of the mesenteries suspend the stomach?

Answer 24

Dorsal and ventral.

Question 25

What happens to the stomach in week 5?

Answer 25

Differential growth forms the greater curvature - i.e. the dorsal wall grows faster.

Question 26

Between which weeks does the stomach rotate?

Answer 26

7-8

Question 27

What is the rotation of the stomach around the craniocaudal axis?

Answer 27

90 degrees clockwise. Causes lesser curvature to move from ventral to right. Greater curvature moves from dorsal to left.

Question 28

What happens to the positions of the vagus nerves following stomach rotation in weeks 7-8?

Answer 28

Initally located on the left and right sides of the gut tube. Become rotated so that left vagus is anterior and right posterior.

Question 29

What is the effect of the slight ventrodorsal rotation on the position of the stomach?

Answer 29

Greater curvature faces slightly caudally. Lesser curvature faces slightly cranially.

Question 30

How is the lesser peritoneal sac (omental bursa) formed?

Answer 30

As the stomach rotates around the craniocaudal axis it creates space behind it - the omental bursa. The remaining peritoneal cavity is now the greater sac and the two are connected by the epiploic foramen.

Question 31

Describe the formation of the greater omentum.

Answer 31

Dorsal mesentery (attached to greater curvature of stomach and posterior abdo wall) continues to grow. Reflects back on itself to form an extension of the lesser sac. Ventral and dorsal folds fuse before birth. Posterior layer also fuses with the mesentery of the transverse colon.

Question 32

What is congenital pyloric stenosis?

Answer 32

Narrowing of the pyloric sphincter caused by hypertrophhy of smooth muscle.

Question 33

What is the incidence of pyloric stenosis?

Answer 33

Affects 1 in 500 births. More common in males than females.

Question 34

What are the signs of pyloric stenosis?

Answer 34

Pappable pyloric mass, projectile vomiting and visible peristalsis.

Question 35

What is heterotropic gastric tissue.

Answer 35

Inappropriate differentiation of the gut epithelium can result in ectopic gastric tissue. This produces acid and can lead to inflammation and ulceration in the surrounding area. Damage can result in strictures.

Question 36

What are the origins of the duodenum?

Answer 36

Proximal half is foregut, distal half is midgut.

Question 37

What marks the boundary between the distal and proximal parts of the duodenum?

Answer 37

The common bile duct.

Question 38

In what week does the duodenum elongate?

Answer 38

Week 4 - resulting in ventrally projecting C-shape. Then dragged to the right by the rotating stomach.

Question 39

How does the duodenum become secondarily retroperitoneal?

Answer 39

The dorsal mesentery attached to the duodenum degenerates so that the duodenum lies against the posterior abdo wall.