Session 3, Anatomy, & Development of mid/foregut Flashcards
Which structures does the midgut give rise to?
Small intestine, (most of duodenum)
Caecum + Appendix
Ascending colon
Proximal 2/3 transverse colon.
What is the primary intestinal loop? How does it form?
Loop that forms as midgut elongates, running out of space.
The loop has:
-Superior mesenteric artery as its axis
-Is connected to the yolk sac by the vitelline duct
-Has cranial, & caudal limbs
When does the growth of the primary intestinal loop happen the fastest?
During the 6th week
What happens to the intestines during development?
Liver and intestines growing too fast, not enough room in abdominal cavity.
The intestines herniate out of the abdominal cavity into umbilical cord.
Describe the movements of the intestinal loop during herniation and re-entry into the abdominal cavity?
3 x 90° turns!
- Turn 90° horizontal as they leave the cavity.
-Turn 90° again as they move back in
- And 90° when back in the abdomen, leaving them ‘horizontal’
(look at diagram)
What do the rotations of the intestines in development achieve? Why is it important?
- Forms the loops of small intestine
- Forms the transverse colon (around the SI)
- Forms the caecal bud (caecum + appendix)
What are some abnormalities caused by misfolding of the midgut?
- Only one rotation made = Left sided colon.
- Reversed rotation (only one rotation clockwise) = Transverse colon passes POSTERIOR to duodenum.
When do must midgut defects present? How do they present?
Ususally in neonatal period.
Strangulation / Ischaemia
What is the vitelline duct?
The long narrow tube that joins the yolk sac to the midgut lumen of the developing fetus.
What is a Meckel’s diverticulum?
A defect where the vitelline duct persists causing a diverticulum in the intestine of the midgut.
Which other defects can arise when a vitelline duct persists?
A Vitelline cyst - forms fibrous strands.
A Vitelline fistula - direct communication between umbilicus and intestinal tract.
What is the rule of 2’s for Meckel’s diverticulum?
2% of population
2 feet from ileocaecal valve
Usually detected in under 2’s
2:1 ratio male: female
When is recanalisation suitable? Why?
If the cell growth of a structure becomes too rapid, obliterating the lumen (e.g. oesophagus)
Must be operatively reopened, or stenosis/atresia can occur.
Where do most atresia / stenosis events occur in development?
In the duodenum.
What could be a common cause of projectile vomiting in infants?
Pyloric Stenosis
Hypertrophy of circular muscle around pyloric sphincter.
Causes vomiting as contents of stomach can’t empty as quickly.
What is gastroschisis?
Failure of closure of the abdominal wall during folding of embryo.
Gut tube + derivatives outside body cavity.
What is an omphalocoele?
Persistence of physiological herniation.
not hernia, as hernia has covering of skin
What is an umbilical hernia?
When part of the internals/gut pokes through a weakness in the abdominal wall at the umbilicus (common in infant)
Usually repairs itself within a year after birth.
Which structures does the hindgut give rise to?
- Distal 1/3 transverse colon
- Descending colon
- Rectum
- Superior part of anal canal
- Epithelium of urinary bladder
What is the pectinate line in the anus?
Line which divides anal canal into histologically distinct superior and inferior parts.
(differences in arterial supply, venous & lymphatic drainage, and innervation)
What is the proctodeum?
The junction between two embryonic germ layer, the back ectodermal part of the alimentary canal.
It it will form the lower part of the anal canal.
Describe the cells, innervation and blood supply above the pectinate line.
- Inferior mesenteric artery
- S2, 3 + 4 pelvic parasympathetics
- Columnar epithelium
- Lymph. drainage = internal iliac nodes
Describe the cells, innervation and blood supply below the pectinate line.
- Pudendal artery
- S2, 3 + 4 pudendal nerve
- Stratified epithelium
- Lymph. drainage = superficial inguinal nodes.
What is the difference in sensation in the anal canal above and below the pectinate line?
- Above:
Only sensation is stretch - Below:
Temperature, touch and pain sensitive
Where will the visceral pain from the different gut derivatives be felt?
Visceral pain - poorly localised
- Foregut (+ derivatives) = epigastric
- Midgut = periumbilical
- Hindgut = suprapubic
What are some common hindgut abnormalities?
- Imperforate anus = failure of anal membrane to rupture.
- Anal/ anorectal agenesis
- Hindgut fistulae (e.g. to bladder)
Which midgut/ hindgut structures lose/ have fused mesenteries?
- Duodenum
- Ascending colon
- Descending colon
- Rectum
