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Embryology > Development of the Gastrointestinal Tract: Foregut > Flashcards

Development of the Gastrointestinal Tract: Foregut Flashcards

1
Q

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

A

Superior: oropharangeal membrane Inferior: cloacal membrane

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2
Q

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

A

The vitelline duct.

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3
Q

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

A

Meckel’s diverticulum.

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4
Q

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

A

Endoderm

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5
Q

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

A

Visceral mesoderm.

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6
Q

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

A

Visceral and parietal mesoderm.

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7
Q

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

A

Dorsal mesentery.

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8
Q

What are the boundaries of the dorsal mesentery?

A

Lower oesophagus to cloaca.

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9
Q

What are the boundaries of the ventral mesentery?

A

Lower oesophagus to 1st part of the duodenum.

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10
Q

Into what does the dorsal mesentery develop?

A

The greater omentum and mesocolon.

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11
Q

Into what does the ventral mesentery develop?

A

Lesser omentum and falciform ligament (umbilical vein).

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12
Q

Into what do the vitelline arteries develop?

A

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

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13
Q

Describe the development of the gut tube endoderm.

A
  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

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14
Q

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

A

Duplication, atresia, stenosis.

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15
Q

What are the superior and inferior boundaries of the foregut?

A

Superior - oropharyngeal membrane.

Inferior - first part of the duodenum.

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16
Q

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

A

The respiratory diverticulum.

17
Q

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

A

Tracheoesophageal septum

18
Q

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

A

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

19
Q

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

A

85%

20
Q

In what week does the oesophagus from?

A

Week 4.

21
Q

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

A

Skeletal muscle derived from paraxial mesoderm.

22
Q

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

A

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

23
Q

In what week of development does the stomach appear?

A

4

24
Q

Which of the mesenteries suspend the stomach?

A

Dorsal and ventral.

25
Q

What happens to the stomach in week 5?

A

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

26
Q

Between which weeks does the stomach rotate?

A

7-8

27
Q

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

A

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

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

A

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.

31
Q

Describe the formation of the greater omentum.

A

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.

32
Q

What is congenital pyloric stenosis?

A

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

33
Q

What is the incidence of pyloric stenosis?

A

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

34
Q

What are the signs of pyloric stenosis?

A

Pappable pyloric mass, projectile vomiting and visible peristalsis.

35
Q

What is heterotropic gastric tissue.

A

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.

36
Q

What are the origins of the duodenum?

A

Proximal half is foregut, distal half is midgut.

37
Q

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

A

The common bile duct.

38
Q

In what week does the duodenum elongate?

A

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

39
Q

How does the duodenum become secondarily retroperitoneal?

A

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

Embryology (5 decks)

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