Lecture 5 Development Of The Midgut Flashcards
Primary intestinal loop
The midgut elongates enormously and runs out of space
Therefore makes a loop connected to the yolk sac by the vitelline duct
Has a cranial and caudal limb on a SMA axis
Physiological herniation
6th week of development
Growth of the primary intestinal loop is rapid and elongates
The abdominal cavity is too small therefore the intestines herniate into the umbilical cord
Midgut rotation
Turns 90 degrees to the right during herniation
Turns 90 degrees after herniation
Turns 90 degrees when returning to the abdominal cavity
Therefore - cranial end is on the left of the superior mesenteric artery
Descent of caecal bud
Caecum descends down to the right iliac fossa with the appendix
Malrotation
Incomplete rotation
- midgut only makes one 90 degree turn
- left sided colon
Reversed rotation
- midgut makes one 90 degrees rotation clockwise
- transverse colon passes posterior to the duodenum
Risks associated with midgut defects
Occurs in neonatal period:
Volvulus
- strangulation
- ischaemia
- duodenal obstruction by large intestine
- compression of transverse colon by SMA
- duodenal dilation due to volvulus of small intestine
Vitelline duct defects
The vitelline duct can persist causing:
- vitelline cyst
- vitelline fistula
- Meckel’s diverticulum
Vitelline cyst
forms fibrous bands between the small intestine, vitelline duct and umbilicus
Vitelline fistula
- direct communication between the umbilicus and intestinal tract
Meckel’s diverticulum
Blind ended outpouching of the small intestine with or without fibrous band formation
Especially in the ileum
2% of population
2 ft from the ileocaecal valve
Usually in under 2 yrs old
2x more likely to get it if male
Can contain ectopic pancreatic or gastric tissue
Recanalisation
In some gut structures, cell growth becomes so rapid that the lumen is partially or fully occluded
Recanalisation restores the lumen
Failure of recanalisation
Atresia or stenosis
Where does recanalisation occur?
Oesophagus
Bile duct
Small intestines - duodenum
Atresia
No lumen as completely occluded
Why causes failure of duodenal recanalisation
Vascular accidents
- lower duodenum
- due to volvulus, malrotation or body wall defect
Incomplete canalisation
- upper duodenum
Pyloric stenosis
Hypertrophy of the circular muscle in the region of the pyloric sphincter
Not due to failure of recanalisation
Common in infants
Characteristic symptom of pyloric stenosis
Projectile vomiting
Gastroschisis
Failure of closure of the ventral abdominal wall during embryonic folding
Gut tube and derivatives outside body cavity
Visceral not covered by peritoneum therefore exposed to amniotic fluid
Problems with gut development e.g.
- intestinal atresia
- short inflamed gut
- feeding problems
Less genetic complications therefore better survival than omphalocele
High mortality rate
Omphalocele
Persistent physiological hernia
Abdominal cavity may not grow enough to accommodate viscera
Covered by peritoneum
Associated with genetic complications therefore worse survival rate but can be closed at birth
Structures of the anal canal
Superior anal canal
Pectinate line
Inferior anal canal
Proctodeum
Anal pit
Small depression in the caudal most region of the embryo
The proctodeum ruptures and the ectoderm is pushed up
Above pectinate line
Supplied by: IMA
Innervation: pelvic parasympathetic nerves S2,3,4
Epithelium cells: columnar
Lymph drainage: internal iliac nodes
Below pectinate line
Supplied by: Pudendal artery
Innervation: pudendal nerve S2,3,4
Epithelium cells: stratified squamous
Lymph drainage: superficial inguinal nodes
Sensation above pectinate line
Stretching
Sensation below the pectinate line
Temperature
Pain
Touch
Visceral referred pain
Foregut - epigastrium
Midgut - periumbilical
Hindgut - suprapubic
Hindgut abnormalities
Imperforate anus - failure of anal membrane to rupture
Anal agenesis - incomplete development of anorectum
Hindgut fistula - channel between rectum and bladder
Cranial limb of midgut
Distal duodenum to proximal ileum
Caudal limb of midgut
Distal ileum to proximal 2/3 of transverse colon
Gastrolienal ligament
Dorsal mesentery from stomach to spleen
Lienorenal ligament
Dorsal mesentery from spleen to kidney
Midgut supply, innervation
Supply: superior mesenteric artery and vein
Innervation:
- parasympathetic - vagus nerve
- sympathetic - superior mesenteric ganglion and plexus
Hind gut supply and innervation
Supply: inferior mesenteric artery and vein
Innervation:
- parasympathetic - pelvic nerves S2,3,4
- sympathetic - inferior mesenteric ganglion and plexus
