GI Embryology Flashcards
What are the 3 common defects associated with abnormal recanalisation of the GI tract?
1) Duplications (bit sticking up so have blind ended pouch)
2) Stenosis
3) Atresia (completely blocked)
Which part of the GI tract is most commonly affected by abnormal recanalisation of the GI tract?
Ileum followed by duodenum
What are duplication cysts and what complications can they cause?
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)
What is oesophageal atresia and polyhydramnios?
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
Why does a congenital hiatal hernia occur?
Insufficient elongation of the oesophagus some of the stomach is located supra-diaphragmatically
What does the greater omentum originate from?
Dorsal mesentery
What is congenital pyloric stenosis and what are the clinical signs of it?
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
What is heteroectopic gastric tissue and what damage can it result in?
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
What is the peritoneal attachements of the duodenum and why does it end up situated towards the right?
Secondarily retroperitoneal
Dragged by the rotating stomach
How does the primary intestinal loop communicate with the yolk sac?
Via the vitelline duct
What are the peritoneal attachments of the ascending and descending colon?
Secondarily retroperitoneal
What is the final movement within the abdomen which puts the gut in its final position?
Descent of the cecum
What is the position of the appendix in most individuals and why?
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
Why is the appendix relatively mobile?
Suspended by a mesentery
What is the second most common position of the appendix and what may this affect?
May project inferiorly towards the pelvic brim, this could affect the symptoms and sight of pain in appendicitis
What is Meckel’s/Ileal diverticulum, what are the symptoms and what is the rule of 2s?
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
What is omphalocele, when is it diagnosed and what other malformations is it associated with?
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
What is non rotation of the midgut, are there any symptoms?
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
What is reversed rotation of the midgut?
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
Why can abnormal rotation of the midgut result in volvulus and what can this cause?
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
What are congenital rectourethral and recto vaginal fistulas, what is it caused by? what are the symptoms and how common is it?
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
What is imperforate anus, what is the prognosis?
Failure of anal membrane to degenerate
Usually requires immediate surgery to allow evacuation of faeces
Good long term prognosis in the majority of cases
What is the difference between the enteric plexi in terms of what they innervate?
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
What is Hirschsprung disease/ congenital aganglionic megacolon, what other genetic condition is it associated with and what is the treatment?
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
From which germ layer is the liver formed?
Hepatocytes (parenchyma) come from the endoderm
Haematopoietic, kupffer cells and connective tissue are derived from the mesoderm (cells of the septum transversum)
What is the diaphragm derived from and what germ layer?
Originates as the septum transversum made from mesoderm cells
What are the symptoms of neonatal jaundice?
Yellow sclera and skin
Why does neonatal jaundice occur?
In 60% full term infants the immature liver does not have sufficient glucuronosyltransferase to conjugate bilirubin - cant be excreted
How is neonatal jaundice treated?
Under UV light
Oxidases the bilirubin to a form which can be excreted
Why is neonatal jaundice dangerous?
Kernicterus
Unconjugated bilirubin can cross the BBB
What is biliary atresia?
Hepatic and bile duct epithelium undergo proliferation and recanalisation
Biliary atresia is a failure of either duct to recanalise
What are the symptoms of biliary atresia?
Yellow sclera and skin but doesn’t respond to UV light therapy
Which syndrome is aganglionic mega colon commonly associated with?
Trisomy 21
What is an annular pancreas?
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
Where does ectopic pancreatic tissue commonly occur?
Stomach or duodenum
What are the possible symptoms/problems with ectopic pancreatic tissue?
Usually asymptomatic
Can cause large lesions which can cause obstruction, ulceration of haemorrhage
What percentage of the population have an accessory spleen and where does it commonly form?
10%
Near the hilum of the primary spleen
