GI Embryology

Overview

Developmental derivatives
- foregut (supplied by celiac trunk) → pharynx to duodenum
- midgut (supplied by the superior mesentric artery) → duodenum to transverse colon
- hindgut (supplied by the inferior mesentric artery)→ distal transverse colon to rectum
GI embryologic timeline
- week 6
  - midgut herniates through umbilical ring
- week 10-11
  - rotates 270 degrees counterclockwise around SMA as it returns to the abdominal cavity
abnormal rotation and fixation of the midgut during early fetal life may result in obstruction and volvulus (which may lead to intestinal ischemia)

Pathology

Anterior abdominal wall defects due to failure of
- rostral fold
  - sternal defects result
- lateral fold
  - omphalocele
    - abdominal contents (stomach, liver, intestines, etc.) protrude through umbilical cord and persist outside of the body but covered by peritoneum
    - associated with trisomy 13 and 18
  - gastoschisis
    - failure of lateral body folds to fuse, resulting in extrusion of intestines through umbilical ring but not covered by peritoneum
- caudal fold
  - bladder extrophy is the protrusion of the anterior bladder through the lower abdominal wall
Duodenal atresia
- due to failure to recanalize lumen of intestines
- associated with trisomy 21
- “double bubble” sign
- NOTE: atresia is occlusion of the lumen of the intestines and stenosis is narrowing of the lumen
Jejunal, ileal, and colonic atresia
- due to vascular accident (“apple peel/corkscrew” atresia )
- segment of bowel wrapped around a remnant of mesentary
Congenital pyloric stenosis
- hypertrophy of muscalaris externa causing the pylorus lumen to narrow
  - palpable “olive” mass in epigastric region
  - food obstructs in pyloric region
  - nonbilious and projectile vomiting at about 2 weeks of age
- treatment: surgery
- incidence: 1/600; mainly first born males
Pancreas divisum- failed fusion of the ventral and dorsal pancreatic buds