Embryology - Development of Foregut

Question 1

Where does the foregut start/end?

Answer 1

Oesophagus to duodenum (first bit of SI)

Question 2

When is the primitive gut tube formed?

Answer 2

During embryonic folding - the ventral surface becomes concave in two directions. The sides of the embryo fold in on each other and the head and tail fold toward one another, forming the primitive gut

Question 3

Where does the primitive gut tube extend to/from?

Answer 3

From the oropharyngeal membrane to the cloacal membrane

Question 4

What can the primitive gut tube be divided into during foetal life?

Answer 4

1. Foregut 2. Midgut 3. Hindgut

Question 5

Where does the midgut start/end?

Answer 5

2nd half duodenum to 2/3 along transverse colon

Question 6

Where does the hindgut start/end?

Answer 6

Distal 1/3 transverse colon to superior 2/3 rectum

Question 7

When does cranio-caudal folding occur?

Answer 7

Week 3-4

Question 8

What connects the gut tube to the yolk sac?

Answer 8

Vitelline duct

Question 9

How is the midgut continuous with the yolk sac?

Answer 9

At the vitelline duct

Question 10

Where is the epithelial lining of the primitive gut tube derived from?

Answer 10

The endoderm

Question 11

Where is the smooth muscle and connective tissue of the primitive gut tube derived from?

Answer 11

The surrounding visceral mesoderm

Question 12

What does the visceral and parietal mesoderm also give rise to?

Answer 12

The visceral and parietal peritoneum

Question 13

How is the primitive gut tube suspended from the posterior abdominal wall?

Answer 13

By the dorsal mesentery

Question 14

What is a mesentery?

Answer 14

A double fold of peritoneum that encloses an organ and connects to the body wall

Question 15

What are the organs enclosed by a mesentery called (e.g. gut)?

Answer 15

Intraperitoneal

Question 16

What are the organs not surrounded by peritoneum called (e.g. aorta)?

Answer 16

Retroperitoneal

Question 17

What is function of mesentery?

Answer 17

Acts as route for blood supply, nerve supply and lymphatic drainage for organs

Question 18

Where is the dorsal mesentery?

Answer 18

From lower oesophagus to cloaca

Question 19

Where is the ventral mesentery?

Answer 19

• From lower oesophagus to 1st part of duodenum - Forms lesser omentum and falciform ligament (umbilical vein)

Question 20

What do vitelline arteries give rise to?

Answer 20

Arteries of GIT The vitelline arteries undergo remodelling, losing their connection to the yolk sac to supply the gastrointestinal tract

Question 21

Directly from the aorta, what unpaired arteries supplying the GIT arise?

Answer 21

1. Coeliac trunk –> foregut 2. Sup mesenteric artery –> midgut 3. Inf mesenteric artery –> hindgut

Question 22

How is the definitive gut formed?

Answer 22

Hollow primitive gut tube –> gut tube occluded by proliferation of endoderm derived epithelial lining –> apoptosis of epithelium occurs over next 2 weeks creating vacuoles –> recanalisation (vacuoles coalesce to fully recanalise the gut tube –> definitive hollow gut tube

Question 23

When does proliferation of the endoderm derived epithelial lining that occludes the gut tube occur?

Answer 23

Week 6

Question 24

When do vacuoles coalesce to fully recanalise the gut tube by?

Answer 24

Week 9

Question 25

What is purpose of hollow tube becoming occluded then hollowed again?

Answer 25

How specialised cells are formed

Question 26

What can abnormal recanalisation lead to?

Answer 26

Duplications of the GI tract --\> cyst

Question 27

What can incomplete recanalisation lead to?

Answer 27

Stenosis (narrowing) or blockage (atresia) of the gut tube

Question 28

What is most commonly affected by abnormal recanalisation?

Answer 28

Ileum is most commonly affected followed by duodenum

Question 29

What can duplication cysts lead to?

Answer 29

Bowel obstruction or intussusception (telescoping of proximal part of bowel into distal part)

Question 30

What does the foregut give rise to?

Answer 30

Respiratory diverticulum

Question 31

How is the foregut separated from the respiratory diverticulum?

Answer 31

Tracheoesophageal ridges form tracheoesophageal septum (separating trachea and oesophagus)

Question 32

What occurs when an oesophageal atresia occurs independently of a TOF?

Answer 32

Displacement of the tracheoesophageal septum separates proximal and distal ends of oesophagus

Question 33

What are dangers of oesophageal atresia?

Answer 33

This prevents the foetus from swallowing amniotic fluid and returning it to the mother through the placental circulation – polyhydramnios

Question 34

How are oesophageal atresia's repaired?

Answer 34

Surgical repair results in 85% survival rate

Question 35

When/where does the oesophagus form?

Answer 35

Week 4 caudal to the lung bud

Question 36

How does the oesophagus differ from the rest of the gut tube?

Answer 36

* Like the rest of the gut tube, oesophagus has endodermal epithelial lining and smooth muscle layer from visceral mesoderm. * However, also has some skeletal muscle

Question 37

Where is the skeletal muscle of the oesophagus derived from?

Answer 37

The paraxial mesoderm

Question 38

What happens if the stomach doesn't descend correctly? What is this called?

Answer 38

Some of stomach in thorax (supradiaphragmatically) Congenital hiatal hernia

Question 39

How is a congenital hiatal hernia different from an adult acquired hernia?

Answer 39

Adult --\> top part of stomach slides through opening into thorax due to pressure Congenital --\> failure of oesophagus to elongate

Question 40

When/how does the stomach appear?

Answer 40

In 4th week as a dilation of the foregut

Question 41

How is the stomach suspended in the abdomen?

Answer 41

By the dorsal and ventral mesenteries

Question 42

What is the lesser omentum?

Answer 42

Ventral mesentery that goes from lesser curvature of stomach to liver

Question 43

What is the falciform ligament?

Answer 43

From liver to anterior wall, derivative of mesentery

Question 44

How does the greater curvature form?

Answer 44

Differential growth in week 5 forms the greater curvature (i.e. the dorsal wall)

Question 45

How/when does the stomach rotate?

Answer 45

•In weeks 7-8, the stomach underdoes rotation around 2 axes

Question 46

How does the lesser curvature move during stomach rotation?

Answer 46

•90° clockwise rotation around the craniocaudal axis causes the lesser curvature to move from ventral position to the right.

Question 47

How does the greater curvature move during stomach rotation?

Answer 47

The greater curvature moves from dorsal position to the left

Question 48

How are the vagus nerves moved during stomach rotation?

Answer 48

The vagus nerves are initially located on left and right sides of the gut tube but are also rotated such that the left vagus trunk becomes anterior and the right becomes dorsal (posterior)

Question 49

There is also some rotation around the ventrodorsal axis. How does this affect the lesser/greater curvatures?

Answer 49

- the greater curvature faces slightly caudally - the lesser curvature slightly cranially

Question 50

As the stomach rotates around the craniocaudal axis, it creates a space behind it. What is this called? What is the remaining peritoneal cavity now known as?

Answer 50

•the lesser peritoneal sac (omental bursa) - The greater sac

Question 51

What connects the greater and lesser sacs?

Answer 51

The epiploic foramen (of Winslow) --\> a narrow opening

Question 52

What are greater and lesser peritoneal sacs created by?

Answer 52

Rotation of stomach

Question 53

How does the stomach attach to the posterior wall?

Answer 53

Via the dorsal mesentery (dorsal mesentery attached to the greater curvature of the stomach) and the posterior abdominal wall (dorsal mesentery) continues to grow rapidly.

Question 54

The dorsal mesentery folds back on itself to form what?

Answer 54

Reflects back on itself to form an extension of the lesser sac (omental bursa) --\> 4 layers

Question 55

What does greater omentum attach to?

Answer 55

Posterior wall

Question 56

The ventral and dorsal folds fuse before birth. What does the posterior layer of the greater omentum also fuse with?

Answer 56

The mesentery of the transverse colon

Question 57

What is congenital pyloric stenosis?

Answer 57

Narrowing of pyloric sphincter caused by hypertrophy of smooth muscle

Question 58

Is pyloric stenosis more common in men or women?

Answer 58

More common in males 5:1

Question 59

What is effect of pyloris stenosis?

Answer 59

* Restricts gastric emptying which can lead to dilation of the stomach * Signs include: ØPalpable pyloric mass ØProjectile vomiting ØVisible peristalsis

Question 60

What can inappropriate epithelial differentiation of the gut tube lead to?

Answer 60

Ectopic gastric tissue

Question 61

What can ectopic gastric tissue lead to?

Answer 61

* Due to acid production, this can cause inflammation and ulceration in the surrounding area * Damage can result in strictures due to scarring or rupture of the gut wall

Question 62

What is the duodenum continuous with?

Answer 62

Duodenum

Question 63

When does the duodenum elongate? What does it result in? What then happens?

Answer 63

Week 4 - resulting in a ventrally projecting C-shape This is then dragged to the right by the rotating stomach

Question 64

What happens to the dorsal mesentery attached to the duodenum?

Answer 64

Degenerates so that the (majority) duodenum lies against the posterior abdominal wall – **secondarily retroperitoneal**

Question 65

What is oesophageal stenosis?

Answer 65

* Occurs when the oesophagus fails to recanalise * Typically associated with polyhydramnios prenatally. * Postnatally, the child will regurgitate IMMEDIATELY upon feeding. * However, there is usually NOT a tracheoesophageal fistula, so the lungs will usually NOT be congested.