Progression of midgut occurs in following steps :
- Primary intestinal loop formation
- Physiological intestinal herniation
- Rotation of midgut
Primary intestinal loop formation
- Midgut is suspended from dorsal abdominal wall.
- Apex of midgut is in contact with yolksac via VITELLO-INTESTINAL DUCT / YOLK STALK(remnant forms meckels diverticulum)
- Cephalic column of midgut - forms distal duodenum,jejunum,proximal illeum
- Caudal column of midgut - forms distal illeum,caecum,appendix,ascending colon,2/3rd transverse colon
Physiological intestinal hernia
- @ 4th week : rapid elongation of midgut occurs after suspension however abdominal cavity is not large enough to accumalate midgut so herniation of midgut occurs through umbilicus
- @ 6th week : retraction of herniated loops occurs because abdominal cavity has expanded along with regression of mesonephric kidneys and decrease liver growth all contributing to expansion og abdominap cavity
- Proximal Jejunum is first to enter back and lies on left side
- All other loops lie on right side
- Caecum temporarily lies in right hepatic region and gradually descends down to right iliac fossa.During its descend appendix is formed
Rotation of midgut
- Occurs around superior mesentric axis
- In anticlockwise direction
- ~270° = 90° during herniation + 180° during retraction of hernia
SIGNIFICANCE
1) Omphalocele
- Herniation of viscera through umbilical ring
- Due to failure of physiologically herniated intestinal retraction
- Associated with chromosomal anomalies(50%),cardiac anomalies(50%),neural anomalies(40%)
2) Gastroschisis
- Herniation through abdominal wall and not through umbilicus
- Direct exposure to amniotic fluid causing damage to viscera
3) Vitellointestinal duct anomalies
- Meckels diverticulum-lies @ 40 to 60 cm proximal to ileocaecal junction,on antimesentric border
- Meckels cyst
- Meckels fistula
