Development of Midgut
Dr. Rania Gabr
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.
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.
Stages of Midgut Development
•
•
•
•
Physiological umbilical hernia
Rotation of the midgut loop
Retraction of herniated midgut loops to Abdomen
Fixation of intestines
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.).
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.
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.
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.
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.
90°
180°
270°
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, retrocolic and pelvic appendix
Development of cecum and Appendix
Positions of Appendix
Mesenteries of the intestinal loops
• Mesentery proper
• Mesentery of ascending & descending
colon (dorsal mesocolon)
• Appendix, lower end of cecum & sigmoid
colon
• Transverse mesocolon
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.
Fixation of various parts of intestines
The enlarged colon presses
the duodenum & pancreas
against the posterior
abdominal wall. C & F
Intestines prior to fixation
Intestines after fixation
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
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.
• 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.
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 by skin & 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.
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
•
Abnormal rotation of gut
Gut Atresia and Stenosis