GI Embryology

Question 1

What are the 3 common defects associated with abnormal recanalisation of the GI tract?

Answer 1

1) Duplications (bit sticking up so have blind ended pouch)
2) Stenosis
3) Atresia (completely blocked)

Question 2

Which part of the GI tract is most commonly affected by abnormal recanalisation of the GI tract?

Answer 2

Ileum followed by duodenum

Question 3

What are duplication cysts and what complications can they cause?

Answer 3

Due to abnormal recanalisation of the gut tube, the cysts are the bit sticking out
Have a high incidence of complications such as bowel obstruction or intususception (telescoping of proximal part of bowel into distal part)

Question 4

What is oesophageal atresia and polyhydramnios?

Answer 4

Can happen independently of a tracheoesophageal fistula, displacement of the tracheoesophageal septum separates proximal and distal parts of the oesophagus - this prevents the fetus from swallowing amniotic fluid and returning it to the mother via the placental circulation - massive pregnancy as lots of amniotic fluid
Surgical repair results in 85% survival rate

Question 5

Why does a congenital hiatal hernia occur?

Answer 5

Insufficient elongation of the oesophagus some of the stomach is located supra-diaphragmatically

Question 6

What does the greater omentum originate from?

Answer 6

Dorsal mesentery

Question 7

What is congenital pyloric stenosis and what are the clinical signs of it?

Answer 7

Narrowing of pyloric sphincter caused by hypertrophy of smooth muscle
Affects 1 in 500 births
More common in males than females 5:1
Restricts gastric emptying which can lead to dilatation of the stomach
Clinical signs - palpable pyloric mass, visible peristalsis, projectile vomiting

Question 8

What is heteroectopic gastric tissue and what damage can it result in?

Answer 8

Inappropriate epithelial differentiation of the gut tube (during recanalisation) can lead to ectopic gastric tissue
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 wall

Question 9

What is the peritoneal attachements of the duodenum and why does it end up situated towards the right?

Answer 9

Secondarily retroperitoneal

Dragged by the rotating stomach

Question 10

How does the primary intestinal loop communicate with the yolk sac?

Answer 10

Via the vitelline duct

Question 11

What are the peritoneal attachments of the ascending and descending colon?

Answer 11

Secondarily retroperitoneal

Question 12

What is the final movement within the abdomen which puts the gut in its final position?

Answer 12

Descent of the cecum

Question 13

What is the position of the appendix in most individuals and why?

Answer 13

The retrocaecal position, the appendix develops as a worm like diverticulum of the cecum and due to the descent of the cecum, ends up retroperitoneal

Question 14

Why is the appendix relatively mobile?

Answer 14

Suspended by a mesentery

Question 15

What is the second most common position of the appendix and what may this affect?

Answer 15

May project inferiorly towards the pelvic brim, this could affect the symptoms and sight of pain in appendicitis

Question 16

What is Meckel’s/Ileal diverticulum, what are the symptoms and what is the rule of 2s?

Answer 16

Remnant of the vitelline duct creates an outpocketing of the ileal wall, most common GI congential malformation 
Usually asymptomatic but may contain ectopic pancreatic or gastric tissue causing inflammation, ulceration and bleeding
Rule of 2s
2inches long
Affects 2% of the population
2 feet from ileocecal junction 
Symptomatic in 2% of cases
2 times more common in males

Question 17

What is omphalocele, when is it diagnosed and what other malformations is it associated with?

Answer 17

Failure of the midgut to return to the abdomen within week 10
Associated with other malformations and increased risk of mortality eg. cardiac or neural tube defects
Diagnosed pre natally using ultrasound
Varies in size - Can be just intestines or may contain other organs eg. liver
Different to gastroschisis as gut wall has formed, they are protected by umbilical chord

Question 18

What is non rotation of the midgut, are there any symptoms?

Answer 18

Midgut undergoes initial 90 degree rotation anti clockwise but fails to undergo 180 degree rotation anticlockwise after that, end up with small intestine on the right side and colon on the left (left sided colon)
Usually asymptomatic

Question 19

What is reversed rotation of the midgut?

Answer 19

Midgut undergoes initial 90 degree rotation anti clockwise but then undergoes 180 degree rotation clockwise instead of anti clockwise
Everything sits in the abdomen in the correct order but duodenum lies ventral to transverse colon

Question 20

Why can abnormal rotation of the midgut result in volvulus and what can this cause?

Answer 20

End up with ports that would normally be retroperitoneal being intraperitoneal and remain suspended by the dorsal mesentery
This can lead to volvulus (twisting) of the midgut
Causes acute obstruction of the small bowel which can cause bilious vomiting (vomiting green bile)
Can constrict arterial supply leading to ischaemia and infarction

Question 21

What are congenital rectourethral and recto vaginal fistulas, what is it caused by? what are the symptoms and how common is it?

Answer 21

Hindgut connected to the urethra (males) or vagina (females)
Caused by abnormal cloaca eg. too small or failure of urorectal septum to extend caudally
Symptoms = faeces and gas in the urethra or vagina
Uncommon, affects 1/5000 births

Question 22

What is imperforate anus, what is the prognosis?

Answer 22

Failure of anal membrane to degenerate
Usually requires immediate surgery to allow evacuation of faeces
Good long term prognosis in the majority of cases

Question 23

What is the difference between the enteric plexi in terms of what they innervate?

Answer 23

Myenteric (Auerbach’s) plexus between circular and longitudinal muscle layers coordinates muscle contraction
Submucosal (Meissner’s) plexus between the circular muscle layer and mucosa regulates secretion
Derived from neural crest cells, ectoderm origin

Question 24

What is Hirschsprung disease/ congenital aganglionic megacolon, what other genetic condition is it associated with and what is the treatment?

Answer 24

Failure of neural crest cells to migrate to the bowel
Absence of enteric ganglia leads to obstruction of the bowel due to lack of peristalsis
Causes dilatation of aganglionic section of bowel - usually rectum and sigmoid colon
Genetic condition most commonly associated with Trisomy 21
Only effective treatment is to remove the affected bowel and anastamose the remaining bowel with the anus

Question 25

From which germ layer is the liver formed?

Answer 25

Hepatocytes (parenchyma) come from the endoderm

Haematopoietic, kupffer cells and connective tissue are derived from the mesoderm (cells of the septum transversum)

Question 26

What is the diaphragm derived from and what germ layer?

Answer 26

Originates as the septum transversum made from mesoderm cells

Question 27

What are the symptoms of neonatal jaundice?

Answer 27

Yellow sclera and skin

Question 28

Why does neonatal jaundice occur?

Answer 28

In 60% full term infants the immature liver does not have sufficient glucuronosyltransferase to conjugate bilirubin - cant be excreted

Question 29

How is neonatal jaundice treated?

Answer 29

Under UV light

Oxidases the bilirubin to a form which can be excreted

Question 30

Why is neonatal jaundice dangerous?

Answer 30

Kernicterus

Unconjugated bilirubin can cross the BBB

Question 31

What is biliary atresia?

Answer 31

Hepatic and bile duct epithelium undergo proliferation and recanalisation
Biliary atresia is a failure of either duct to recanalise

Question 32

What are the symptoms of biliary atresia?

Answer 32

Yellow sclera and skin but doesn’t respond to UV light therapy

Question 33

Which syndrome is aganglionic mega colon commonly associated with?

Answer 33

Trisomy 21

Question 34

What is an annular pancreas?

Answer 34

Ventral bud of a pancreas can be bi lobed, one lobe can rotate ventral to duodenum and the other dorsally
They then surround the duodenum
Can compress the duodenum causing GI obstruction

Question 35

Where does ectopic pancreatic tissue commonly occur?

Answer 35

Stomach or duodenum

Question 36

What are the possible symptoms/problems with ectopic pancreatic tissue?

Answer 36

Usually asymptomatic

Can cause large lesions which can cause obstruction, ulceration of haemorrhage

Question 37

What percentage of the population have an accessory spleen and where does it commonly form?

Answer 37

10%

Near the hilum of the primary spleen