5. Development of the GI Part 2 Flashcards
What does the midgut give rise to?
- Small intestine, including most of duodenum
- Caecum & appendix
- Ascending colon
- Proximal 2/3 transverse colon
What is the first thing to happen to the midgut when it elongates enormously and runs out space?
It loops forming the primary intestinal loop
What connects the primary intestinal loop to the yolk sac?
Vitelline duct
What does the part of the midgut that is connected to the yolk sac by the duct develop into?
Ileum
What forms the axis of the primary intestinal loop and what is the midgut above and below the axis called?
Superior mesenteric artery. Cranial and caudal limbs
Why does physical herniation of the midgut occur?
Liver grows rapidly along with the primary intestinal loop, abdominal cavity too small to accommodate both
Where does the intestine herniate into in physiological herniation and what week does it occur?
Umbilical cord. 6th week
what does the carnial part become?
small intestine
what does the caudal part become?
large intestine
describe the Midgut rotation in steps
• There is a cranial limb and a caudal limb with an axis comprising the Superior Mesenteric Artery
• This group go through a series of counter clockwise 90 degree rotations (if viewed from the
front.
• The result of this is the caudal derivatives end up lying to the right of the cranial derivatives and the transverse colon being on top of the duodenum
What does the midgut rotate around?
superior mesenteric artery
What happens in the first rotation of the midgut?
Cranial limb moves to the right of the SMA, caudal limb moves to the left. Small intestine begins to develop, and herniates into the umblical cord.
What happens in the second rotation of the midgut?
Cranial limb moves below SMA, and caudal limb above. Caecal swelling develops from the caudal limb. Transverse colon begins to move in front of duodenum
What happens in the third rotation of the midgut?
Cranial limb moves to the left of SMA, and caudal limb to the right. Caecum remain at the sub-hepatic region.
At what stage in the rotation of the midgut does it return into the abdominal cavity and which part reenters first?
Returns during the third rotation(10th week), cranial limb enters first and moves to left side. (presence of caecal swelling stops it from entering)
What happens after the third rotation of the midgut?
Elongation of the ascending colon and decent of the caecal bud
what are midgut rotational problems?
Malrotation
Reversed rotation
describe malrotation
• Incomplete rotation
• Midgut loop makes only one 90° rotation
Left-sided colon
describe reversed rotation
- Midgut loop makes one 90° rotation clockwise
* Transverse colon passes posterior to the duodenum
What is the main risk associated with midgut defects?
Volvulus
What is a volvulus?
twisting of the bowel
What can happen to a volvulus?
Can become strangulated and ischaemic
What are 3 abnormalities resulting from persistence of the vitelline duct?
Vitelline cyst, vitelline fistula, Meckel’s diverticulum
How does a vitelline cyst develop?
midportion of the vitelline duct remains patent and each end is obliterated, and mucus then accumulates within the cyst
What is a vitelline fistula?
Failure of the Vitelline duct to obliterate, direct communication between the umbilicus and intestinal tract.
What would you expect to see on a vitelline fistula?
contents of the intestinal tract coming out of the umbilicus.
What is Meckel’s diverticulum?
Small bulge due to out pouching of the small intestine due to failure of the vitelline duct to completely obliterate.
What is the most common GI congenital abnormality?
Vitelline diverticulum
What is the rule of 2’s for a Meckel’s diverticulum?
2% population, 2 feet from ileocaecal valve, detected in under 2’s, 2:1 ratio males:females
What might a Meckel’s diverticulum contain?
Ectopic gastric or pancreatic tissue, intestines are not adapted for gastric secretions
What can happen to the lumen of the gut due to its rapid growth?
Many become partly or completed obliterated.
Which parts of the gut lumen may become obliterated due to rapid growth?
Oesophagus, small intestine, bile duct
What is the process of restoring the lumen in the gut tube where it has been obliterated?
Recanalisation
What can occur if recanalisation is unsuccessful?
Fully unsuccessful = atresia (Lumen obliterated),
partly = stenosis (Lumen narrowed)
What is pyloric stenosis and what is a characteristic sign of this in babies?
o hypertrophy of the circular muscle in the region of the pyloric sphincter
o NOT a recanalisation failure
o Common abnormality of the stomach in infants
o narrowing of the exit from the stomach causes characteristic projectile vomiting
where does atresia/stenosis commonly occur?
duodenum
What is gastroschisis?
Defect of ventral abdominal wall, failure of the wall to close during embryonic folding. Resulting in extrusion of gut tube through abdominal wall. Not covered in peritoneum.
What is the gut tube exposed to in gastroschisis?
Aminotic fluid as it is not covered in peritoneum, which can damage the gut.
What is the prognosis of gastroschisis?
90-95% survival rate, depending on how much of the gut is on the outside
What is omphalocele?
Persistence of physiological herniation, covered in peritoneum - midgut herniation fails to return to abdominal cavity
What is omphalocele often associated with?
With other genetic conditions (often trisomies)
why is omphalocele mortality higher than gastroschisis?
omphalocele associated with other developmental abnormalities
what are the two Anterior abdominal wall defects
gastroschisis
omphalocele
What does the hindgut give rise to?
- Distal 1/3 transverse colon
- Descending colon
- Rectum
- Superior part of anal canal
- Epithelium of urinary bladder
What separates the anal canal into its histological superior and inferior parts?
Pectinate line.
What germ layer is responsible for development of the superior and inferior parts of the anal canal?
Superior = endoderm, inferior = ectoderm
What is the arterial supply to the superior and inferior anal canal?
Superior = IMA, Inferior = Pudendal A
What is the nerve supply to the superior and inferior anal canal?
Superior = S2-4 pelvic parasympathetics, Inferior = S2-4 Pudendal Nerve
What is the lymphatic drainage of the superior and inferior anal canal?
Superior = deep internal iliac nodes, Inferior = Superficial inguinal nodes
What is the epithelial lining of the superior and inferior anal canal?
Superior = columnar epithelium, Inferior = stratified squamous
What is the consequence of two embryonic tissues to the anal canal
- above the pectinate line the only sensation possible is stretch, vague pain
- while below the pectinate line the tissue is temperature, touch and pain sensitive, localised pain
Where does visceral pain from foregut, midgut and handgut localise to?
Epigastric area, periubilical area and suprapubic
What are 3 congenital abnormalities of the anal canal?
Imperforate anus, anal/anorectal genesis, hindgut fistulae (e.g urorectal fistula)
What is imperforate anus?
Failure of anal membrane to rupture, anal opening not present.
what divides the cloaca and into what?
urorectal septum divides the cloaca into urogenital sinus and anorectal canal
what is anorectal genesis?
problems with blood supply to hindgut
Which derivatives of the midgut and hindgut retain their mesenteries?
o Jejunum o Ileum o Appendix o Transverse colon o Sigmoid colon
Which derivatives of the midgut and hindgut become secondary retroperitoneal?
o Duodenum
o Ascending colon
o Descending colon
o Rectum (no peritoneal covering in distal 1/3)
