Development of Midgut

1. Development of Midgut Dr. Rania Gabr

2. Objectives • Give the extent of the midgut. • Define Vitelline duct or yolk stalk. • Discuss the formation of primary intestinal loop. • Explain the mechanism of Midgut Development. • Describe midgut abnormalities.

3. Extent of Midgut • Extend from the duodenum (distal to the opening of bile duct) to the proximal 2/3rd of transverse colon. • In 5th week midgut is suspended from posterior abdominal wall by a short mesentery. • Midgut is connected with yolk sac by vitelline duct or yolk stalk.

5. Stages of Midgut Development • Physiological umbilical hernia • Rotation of the midgut loop • Retraction of herniated midgut loops to Abdomen • Fixation of intestines

6. Physiological herniation • At the biginning of 6th week,the midgut elongates to form a venteral U-shaped midgut (intestinal) loop. • Midgut loop communicates with the yolk sac by vitelline duct or yolk stalk. • As a result of rapidly growing liver, kidneys & gut ,the abdominal cavity is temporarily too small to contain the developing rapidly growing intestinal loop. • So ,Midgut loop projects into the umbilical cord …this is called physiological umbilical herniation (begins at 6th w.).

7. Midgut development • Mid gut is supplied by the superior mesenteric artery. • Elongation of the gut with its mesentery forms the primary intestinal loop. • The intestinal loop has two limbs (cranial and caudal) • At the Apex, the loop is connected with yolk sac by vitelline duct.

9. Midgut development • Superior mesenteric artery runs in the axis, between the 2 limbs. • The cephalic limb forms the distal part of the duodenum, jejunum and part of the ilium. • The caudal limb forms the lower portion of the ilium, cecum, appendix, ascending colon, and proximal 2/3rd of transverse colon.

10. Rotation of midgut • Midgut loop has a cranial limb & a caudal limb. • Midgut loop rotates around the axis of the superior mesenteric artery. • Midgut loop rotates first 90 degrees to bring the cranial limb to the right and caudal limb to left during the physiological hernia. • The cranial limb of midgut loop elongates to form the intestinal coiled loops (jejunum & ileum). • This rotation is counterclockwise and it is completed to 270 degrees, so after reduction of physiological hernia it rotates to about 180 degrees.

12. Retraction of herniated loops • Begins during 10th week. • It is called reduction of physiological midgut hernia. • Factors responsible: • Regression of the mesonephric kidney • Reduced growth of the liver • Expansion of the abdominal cavity • The proximal part of the jejunum is the first part to re-enter & comes to lie on the left. • The cecal bud (cecum) is the last part to re-enter.

14. 90°

15. 180°

16. 270°

18. Development of cecum and Appendix • Cecal bud appears during sixth week, lie at first in the right upper quadrant, then descends to the right iliac fossa. • During its descent, appendix appears as a narrow diverticulum from the distal end of the cecal bud. • Appendix may have different positions,retrocecal, retrocolicand pelvic appendix

19. Development of cecum and Appendix

20. Positions of Appendix

21. Mesenteries of the intestinal loops • Mesentery proper • Mesentery of ascending & descending colon (dorsal mesocolon) • Appendix, lower end of cecum & sigmoid colon • Transverse mesocolon

22. Fixation of various parts of intestine • The mesentry of jejunoileal loops is at first continuous with that of the ascending colon. • When the mesentry of ascending colon fuses with the posterior abdominal wall, the mesentry of small intestine becomes fan-shaped and acquires a new line of attachment that passes from duodenojejunal junction to the ileocecal junction.

23. Fixation of various parts of intestines • The enlarged colon presses the duodenum & pancreas against the posterior abdominal wall. C & F • Most of duodenal mesentery is absorbed, so most of duodenum ( except for about the first 2.5 cm derived from foregut) & pancreas become retroperitoneal. C & F Intestines prior to fixation Intestines after fixation

24. Mid gut Anomalies • Mobile cecum: Persistence of a portion of mesocolon. It may lead to Volvulus or retrocoloic hernia. • Omphalocele: • Herniation of abdominal viscera through an enlarged umbilical ring, covered by amnion. • It is due to failure of the bowel to return to the body cavity from its physiological herniation during 6th to 10th week. • It is associated with other defects such as cardiac anomalies, neural tube defects & chromosomal abnormalities.

26. Gastroschisis: • Protrusion of abdominal contents through the body wall directly into the amniotic cavity not covered by amnion or peritoneum. • The bowel may be damaged by exposure to the amniotic fluid. • This defect is due to the abnormal closure of the body wall around the connecting stalk. • It occurs lateral to the umbilicus usually on the right.

27. Umbilical Hernia • The intestines return to abdominal cavity at 10th week, but herniate through an imperfectly closed umbilicus • It is a common type of hernia. • The herniated contents are usually the greater omentum & small intestine. • The hernial sac is covered byskin &subcutaneous tissue. • It protrudes during crying,straining or coughing and can be easily reduced through fibrous ring at umbilicus. • Surgery is performed at age of 3-5 years.

28. Vitelline Duct Abnormalities • 2% of people, 2 -feet away from Ileo-cecal valve, 2 -inches long. • Persistence of Vitelline duct forms: Meckel’s diverticulum or ileal diverticulum • Other related structures are enterocystoma or vitelline cyst, umbilical fistula or vitelline fistula and vitelline ligaments

30. Abnormal rotation of gut

31. Gut Atresia and Stenosis