Embryology Development & Congenital anomalies of the GI tract Flashcards
What are the derivatives of the foregut?
Oesophagus Trachea and lung buds stomach Duodenum proximal to entrance of bible duct Liver, biliary apparatus and pancreas
What are the derivatives of the midgut?
Duodenum distal to opening of bile duct
Small intestine
Caecum and appendix
Ascending colon and 2/3rds of transverse
What are the derivatives of the hindgut?
Distal 3rd of transverse colon, descending colon, sigmoid colon
Rectum and superior part of anal canal
Epithelium of bladder & most of urethra
What is the arterial supply to the foregut?
Coeliac trunk
What is the arterial supply to the midgut?
SMA
What is the arterial supply to the hindgut?
IMA
Describe the characteristics of the oesophageal muscle, upper 2 res vs lower 1 third
Upper 2/3: Striated muscle innervated by vagus nerve
Lower 1/3: Smooth muscle innervated by splanchnic plexus
Describe the rotation of the stomach.
Turns 90 degrees on the longitdinal axis so left side is anterior and right posterior
AP rotation, caudal part moves right and upward
Where is the lesser omentum
between lesser curve of stomach and liver
Where is the falciform ligament
liver to ventral wall of abdominal wall
At what week does haematopoiesis begin giving the liver its read appearance
week 6
At what week does bile formation start?
Week 12 → dark green bowel contents
Briefly describe the embryology of the pancreas.
Th larger dorsal pancreatic bud develops 1st, a ventral pancreatic pub develops near the entry of the bille duct.
The dorsal pud is a accessory duct to the duodenum (minor papilla) and the ventral bud has the main pancreatic duct (major papilla)
As the duodenum rotates the two buds form and the main duct remains patent whilst the accessory duct closes. This fails to close in 10%.
When does insulin secretion start?
Month 5 - islets of langerhan
Why does physiological herniation of the midgut occur?
As the midget elegonates rapidly as does the size of the liver, there is not enough space within the developing abdominal cavity, therefore at week 6 the loops entry the extra embryonic cavity in the umbilical cord → physiological herniation
It renters at week 10.
Which is the last part of the gut to reenter the abdominal cavity
Caecum
Then descends in LIF, as descends appendix produced as a diverticulum
What structures are retroperiteonal (anterior side has peritoneum)
Duodenum (except fist 2.5cm)
Ascending colon
Descending colon
What structures retain their free mesenteries
Jejenum and ileum
Lower and of caecum and appendix
Transverse colon (fuses with posterior wall o f greater omentum)
Sigmoid colon
Describe the connection of the urogenital system and hindgut at week 5
The allantois (future urogenital sinus) and hindgut unite at the cloaca (all endoderm) which comes into contact with the surface ectoderm at the cloacal membrane.
An area of mesodermal tissue between the allantois and hindgut→ the urorectal septum
How does the allantois/hingut/urorectal change as the future develops
The urorectal septum moves closer to the cloacal memabrane/
At week 7 the cloacal membrane breaks down which creates an opening of the anal canal and a ventral opening for the urogenital sinus. The tip of the urorectal septum forms the perineal body.
Proliferation of the ectoderm → proctodeum the lowest region of the anal canal
Describe the embryological orgins of the anal canal
Superior 2/3 endoderm of the hindgut
Inferior 1/3 ectoderm of proctoderm
Junction pectinate late, just below anal columns
Arterial supply of superior 2/3rds of anal canal
Superior rectal artery (cont. of IMA)
Arterial supply of inferior 1/3rd of anal canal
Inferior rectal artery (branch of internal pudendal artery)
Venous drainage of superior 2/3rds of anal canal
Superior renal vain (inferior mesenteric vein)
Venous drainage of inferior 1/3rd of anal canal
inferior rectal vein (internal pudendal vein)
Lymphatic drainage
- superior 2/3rds of anal canal
- inferior 1/3rd of anal canal
- Inferior mesenteric nodes
- Superficial inguinal lymph noses
Nerve supply
- superior 2/3rds of anal canal
- inferior 1/3rd of anal canal
- Autonmoic nervous system ‘painless carcinoma’
- Inferior rectal nerve
How does oesophageal atresia present antenatally & postnatally
80-90% is associated with what additional abnormality
Antenatal: polyhydramnios
Postnatal: excessive drooling and regurgitation, inability to pass NG tube
trachea-oesophageal fistula
Maybe associated with anorectal atresia dan abnormality of urogenital system
Where does duodenal stenosis most often occur?
What syndrome is it associated with?
How does it present antenatally & post nataly
What is the sign on XR?
Failed recanulisation - junction of the bile duct/pancreatic duct
Associated with downs syndrome (1/3)
AN: Polyhydramnios
PN: Bilious vomit abd distension of epigatrum
XR: Double bubble sign
What does Kasai portoenterostomy treat?
Congenital extraheptic biliary atresia
What is an annular pancreas
Ventral bud of pancreas move in opposite directions around the duodenum.
What is the difference between gastroschsis and omphalocele
Gastrochesis: herntaiton of the abdominal contents, not covered by peritoneum through the para umbilical defect.
Omphalocele: Herniation of abdominal viscera covered in amnion through umbilical vein, failure of return of physiological herniation
What is the prognosis of gastroschsis and omphalocele
Gastroshsis - good, surgical repair
omphalocele - often associated with other genetic abnormalities (cardiac/neural tube) - depends on this. High mortality rate 25%
What is a meckle diverticulum? Where does it occur?
Persisting small portion of vitelline duct, forming outpocketing of diverticulum. Approx 40-60cm from ileocaecal valve
can mimic appendicitis
What is the cause of congenital megacolon (hirschsprung)?
Absent parasymapthetic ganglia in the bowel wall, neural crest cells fail to migrate into the wall of the colon.
