Development Of The Gut 3 Flashcards
Where do the bile duct + pancreatic duct enter the duodenum?
Midpoint of D2
Outline the rotation of the midgut
- cranial portion > small intestines
- caudal portion > large intestine
- 3 x 90° rotation results in SI on left + LI on right
- caecum descends
Outline the physiological herniation of the midgut
- the midgut grows faster than the abdominal cavity so in week 6 the intestinal loop herniates into the umbilical cord
- this forms a loop with the superior mesenteric artery which undergoes 3 x 90° rotations
- in week 10 the loop returns to the abdominal cavity
What rotational developmental problems can occur in the midgut?
- one 90° rotation: left sided colon
- reversed one 90° rotation: normal LR layout but transverse colon is behind SI
- small intestine is R/L
- large intestine is R/L
- transverse colon is superior or inferior
- small intestine: left
- large intestine: right
- transverse colon: superior
What is an omphalocoele?
The persistence of the physiological herniation of midgut
What is gastroschisis?
Failure of closure of the abdominal wall following folding of the embryo > gut tube + derivates outside the body cavity
What is the difference between omphalocoele and gastroschisis?
- omphalocoele: midgut structure have peritoneal covering > NOT EXPOSED to amniotic fluid
- gastroschisis: failure of abdominal wall to form properly > midgut structure NOT COVERED in peritoneum > exposed to amniotic fluid > negatively affects gut development
- Lower mortality in gastroschisis
Why is gastroschisis surgery complicated?
The abdominal cavity may not be big enough to fit the herniated structures
When does the vitelline duct regress?
Week 7
What are three vitelline duct abnormalities?
- vitelline cyst
- vitelline fistula
- Meckel’s diverticulum
What is the rule of twos for Meckel’s diverticulum?
- 2% of population
- located 2 feet proximal to ileo-caecal valve
- detected in under twos
- 2:1 ratio M:F
What is recanalisation failure?
Partial or unsuccessful of recanalisation
Partial > stenosis
Unsuccessful > atresia
What is pyloric stenosis?
Hypertrophy of pyloric sphincter
NOT recanalisation failure
What does pyloric stenosis cause in infants?
Projectile vomiting
What serves as the axis for the intestinal loop during midgut development?
Superior mesenteric artery
How does the cloaca divide?
- in the 4-7th week
- urorectal septum descends + divides cloaca into urogenital sinus + anorectal canal
What is the urorectal septum?
A piece of mesoderm which divides the cloaca
What does the cloaca divide into?
Urogenital sinus
Anorectal canal
What is the proctodeum?
Back ectodermal part of the anorectal canal
What is the pectinate line in terms of epithelia?
Line between the ectoderm derived stratified squamous epithelia + endoderm derived columnar epithelia (gut)
What is the difference in pain detection above + below the pectinate line?
- above: vague pain in response to stretch + chemical injury
- below: localised pain (somatic)
What is the blood supply above and below the pectinate line?
- above: gut blood supply
- below: systemic blood supply
What are 3 hindgut abnomalities?
- imperforate anus
- anorectal agenesis
- fistulae
What is an imperforate anus?
Failure to rupture anal membrane > absence of a normal anal opening
What is anorectal agenesis?
Hindgut fails to form due to problems with blood supply > anus doesn’t form
What is fistulae?
Abnormal connection between two hollow epithelial lined cavities
e.g. rectum + vagina/bladder
Name the peritoneal recesses
Rectouterine pouch (women)
Rectovesicle pouch (men)
Vesicouterine pouch (women)
Hepatorenal recess
Subdiaphragmatic recess
Paracolic gutter
List the retroperitoneal structures
SADPUCKER
- Superarenal (adrenal) glands
- Aorta + IVC
- Duodenum D2+D3
- Pancreas
- Ureters
- Colon ascending + descending
- Kidenys
- Esophagus
- Rectum
