2. OBJECTIVES
After completion of this session, the students should be able to
1. Relate embryonic enfolding to the formation of the primary gut tube.
2. List the parts of the primary gut tube.
3. Define the position and extent of dorsal and ventral mesenteries.
4. Describe the formation of the esophagus and lung bud.
5. Describe the rotation of the stomach.
6. Describe the formation of the
Omental bursa. Pancreas. Greater omentum.
7. List the derivates of the ventral mesogastrium.
8. Discuss the rotation and recanalization of the duodenum.
9. Illustrate the formation of the primary intestinal loop.
10. Understand the formation of the physiological umbilical hernia.
11. Describe the rotation, coiling of the midgut, & retraction of herniated loops.
12. Outline the development of the cecum.
13. List the derivatives of the hindgut and cloaca.
14. Recognize the dual origin of the anal canal.
15. Congenital anomalies of the GIT development Dr M Eladl
3. DEVELOPMENT OF THE GIT
The primitive gut is formed by incorporation of yolk sac
during foldings
1. Closed at its cranial end by the oropharyngeal membrane that
breaks down at the stomodeum.
2. Closed at its caudal end by the cloacal membrane that breaks
down at the proctodeum.
Dr M Eladl
4. DEVELOPMENT OF THE GIT
The digestive tract is divided
based on vascular supply into
1. Foregut: Coeliac trunk
2. Midgut: Superior Mesenteric A
3. Hindgut: Inferior Mesenteric A
Dr M Eladl
5. VENTRAL AND DORSAL
MESENTERIES AND THEIR FATES
1. Ventral mesentery:
- Exists only in the region of the
terminal part of the esophagus,
the stomach, and the upper part
of the duodenum.
- Derived from septum
transversum.
- Growth of the liver divides the
ventral mesentery into:
- lesser omentum.
- falciform ligament.
Dr M Eladl
6. VENTRAL AND DORSAL
MESENTERIES AND THEIR FATES
2. Dorsal mesentery:
- Suspends the caudal part
of the foregut, the
midgut, and a major part
of the hindgut from the
abdominal wall.
- Forms
- Dorsal mesogastrium
- Dorsal
mesoduodenum
- Dorsal mesentery of
the jejunal and ileal
loops forms the
mesentery proper.
- Dorsal mesocolon Dr M Eladl
7. VENTRAL AND DORSAL
MESENTERIES AND THEIR FATES
The Dorsal mesogastrium:
- Most of it forms the greater omentum
- The dorsal mesogastrium between the stomach and spleen
becomes the gastrosplenic ligament and the part between
the spleen and kidney becomes the lienorenal (splenorenal)
ligament.
- The spleen remains intraperitoneal
Dr M Eladl
8. DEVELOPMENT OF THE
FOREGUT
Derivatives of the foregut are:
1. Primitive pharynx and its derivatives (oral cavity,
pharynx, tongue, tonsils, salivary glands and upper
respiratory system).
2. Lower respiratory system.
3. The esophagus and stomach.
4. Duodenum, proximal to the opening of the bile duct.
5. The liver, biliary apparatus (hepatic ducts, gall
bladder, and bile duct), and pancreas.
The coeliac trunk supplies all these derivatives except:
– Pharynx
– Most of the oesophagus.
– Respiratory tract Dr M Eladl
9. DEVELOPMENT OF THE
ESOPHAGUS
1. Division of the cranial part of
the foregut immediately
caudal to the primitive
pharynx to: Trachea (anterior)
& Esophagus (posterior).
2. Initially, the esophagus is
short.
3. Due to the growth and
descent of the heart and lungs
it elongates.
4. Temporary obliteration of the
lumen occurs due to
proliferation of the epithelium.
5. Recanalization of the lumen
occurs by the end of the
embryonic period.
Dr M Eladl
10. DEVELOPMENT OF THE
ESOPHAGUS
Dr M Eladl
6. The epithelium and glands
are derived from
endoderm.
7. The striated muscle in the
upper 2/3 of the
oesophagus and the
smooth muscles of the
lower 2/3 is derived from
the mesoderm.
11. ANOMALIES OF THE
OESOPHAGUS
1. Esophageal atresia:
DUE TO deviation of the tracheo-
esophageal septum in a posterior
direction OR failure of
recanalization of the oesophagus.
Features:
– Associated with
tracheoesophageal fistula:
There is incomplete separation
of the esophagus from the
laryngo – tracheal tube.
– Associated prematurity (about
1/3).
– A fetus is unable to swallow the
amniotic fluid. This results in
polyhydramnios.
Dr M Eladl
12. ANOMALIES OF THE
OESOPHAGUS
3. Short oesophagus & congenital hiatal hernia:
The oesophagus fails to elongate so it is very short
and may be associated with thoracic stomach.
Dr M Eladl
2. Esophageal stenosis:
Due to incomplete recanalization of oesophagus.
13. DEVELOPMENT OF THE
STOMACH
Around the middle of the 4th week.
Develops from the distal part of the foregut.
It is initially a simple tube.
Dr M Eladl
14. DEVELOPMENT OF THE
STOMACH
Slight dilatation in the
stomach occurs and the
stomach becomes
fusiform in shape.
The posterior border
grows faster than its
anterior border. This
result in the anterior
border becomes the
lesser curvature & the
posterior border
becomes the greater
curvature.
Dr M Eladl
15. ROTATION OF THE STOMACH
Rotation is due to:
– Differential growth of the stomach.
– Growth of the liver.
Dr M Eladl
Rotation of the stomach 90 degree in a clockwise
direction around both the longitudinal and transverse
axes of the stomach:
16. RESULTS OF ROTATION OF
THE STOMACH
Around its longitudinal axis:
– The anterior border (lesser curvature): becomes right
– The posterior border (greater curvature) becomes left.
– The left side becomes anterior surface.
– The right side becomes posterior surface.
Dr M Eladl
17. RESULTS OF ROTATION OF
THE STOMACH
Around its transverse axis:
– Before rotation:
The cranial & caudal ends of the stomach are in the
median plane.
– After rotation:
The cranial end moves to the left and slightly inferiorly,
and its caudal end moves to the right and superiorly.
The long axis of the stomach becomes transverse to the
long axis of the body.
Dr M Eladl
18. RESULTS OF ROTATION OF
THE STOMACH
The rotation explains
why the left vagus
nerve supplies the
anterior wall of the
adult stomach and the
right vagus nerve
innervates its
posterior wall.
Dr M Eladl
19. DEVELOPMENT OF OMENTAL
BURSA
The lesser sac of peritoneum:
Rotation of the stomach is thought to pull the dorsal
mesogastrium to the left and the lesser sac becomes
expanded transversely between the stomach and the
posterior abdominal wall.
Dr M Eladl
20. ANOMALIES OF THE STOMACH
Congenital hypertrophic pyloric stenosis:
– The circular muscles in the pyloric region are
hypertrophy. This result in stenosis of the pyloric canal.
Dr M Eladl
21. ANOMALIES OF THE STOMACH
Thoracic stomach:
– Due to the short oesophagus, the stomach is displaced
superiorly through the esophageal opening
Dr M Eladl
22. ANOMALIES OF THE STOMACH
Hour-glass stomach:
– A constriction in the middle
of the stomach divided it
into two dilated portions.
– It occurs in adults due to
chronic peptic ulceration
there is fibrosis and
contracture of the stomach
leading to an hourglass
shape as well as altered
mobility
Dr M Eladl
23. ANOMALIES OF THE STOMACH
Transposition of the stomach to the right side:
– Due to rotation 90 degree in an opposite direction.
– The lesser curvature moves to the left and the greater
curvature moves to the right.
– The left vagus nerve supplies the posterior wall of the
stomach and the right vagus nerve innervates it
anterior wall.
Dr M Eladl
24. DEVELOPMENT OF THE
DUODENUM
In the 4th week.
Begins to develop from the
endoderm of the caudal part
of the foregut and the cranial
part of the midgut.
The developing duodenum
grows rapidly, forming a C-
shaped loop that projects
ventrally.
Dr M Eladl
25. DEVELOPMENT OF THE
DUODENUM
The duodenum is attached to the posterior abdominal wall
by dorsal mesoduodenum and with the liver and anterior
abdominal wall by ventral mesoduodenum.
Dr M Eladl
26. DEVELOPMENT OF THE
DUODENUM
As the stomach rotates, the
duodenal loop rotates to the
right and the dorsal
mesoduodenum fuses with
the peritoneum of the
posterior abdominal wall and
both disappear.
By the end of the embryonic
period, most of the ventral
mesoduodenum has
disappeared.
The lumen of the duodenum
becomes obliterated because
of the proliferation of its
epithelial cells.
Latter recanalization occurs. Dr M Eladl
27. BLOOD SUPPLY OF THE
DUODENUM
The duodenum is supplied by branches of the celiac and
superior mesenteric arteries because of its derivation from
the foregut and midgut.
Dr M Eladl
28. ANOMALIES OF THE
DUODENUM
Duodenal stenosis:
– Due to incomplete
recanalization of the
duodenum.
Duodenal atresia:
– Due to failure of
recanalization of the
duodenum.
– Polyhydramnios also
occurs because
duodenal atresia
prevents normal
absorption of amniotic
fluid by the intestine.
Dr M Eladl
29. DEVELOPMENT OF LIVER &
BILIARY PASSAGES
In the 4th week.
The liver arises as a ventral diverticulum from the caudal
part of the foregut. This hepatic diverticulum (liver bud)
extends into the septum transversum (mass of splanchnic
mesoderm between the developing heart and midgut).
Dr M Eladl
30. DEVELOPMENT OF LIVER &
BILIARY PASSAGES
The hepatic diverticulum enlarges rapidly and divides into
two parts as it grows between the layers of the ventral
mesentery
Dr M Eladl
31. PARS HEPATICA
It is the larger cranial part of the hepatic diverticulum.
Gives rise to:
– Hepatic cells:
– Hepatic sinusoids:
– Kupffer cells & hematopoietic tissue.
The liver grow rapidly to fill a large part of the abdominal cavity.
At first, the 2 lobes are of the same size but soon the right become
larger.
Bile formation start during the 12th week.
Dr M Eladl
32. PARS CYSTICA
Becomes the gall bladder and the stem of the diverticulum forms
the cystic duct.
The stalk connecting the hepatic and cystic ducts to the
duodenum becomes the common bile duct.
The right and left branches of the pars hepatica become
canalized to form the right and left hepatic ducts. Dr M Eladl
33. FORMATION OF THE CAPSULE AND
LIGAMENTS OF THE LIVER:
As the septum transversum is
penetrated by the growing pars
hepatica.
– The mesoderm of the septum
transversum between the
liver and the anterior
abdominal wall becomes the
FALCIFORM LIGAMENT.
– The mesoderm of the septum
transversum between the
liver and the foregut
(stomach and duodenum);
form the LESSER OMENTUM.
– The mesoderm on the
surface of the liver
differentiates into CAPSULE
AND PERITONEAL
COVERING Dr M Eladl
34. SIZE & WEIGHT OF THE LIVER
The liver is large in fetal life (about 10% of total body weight at
the 10th week) due to:
– Large blood sinusoids.
– It is the main hemopoietic organ forming the blood cells, which
begins during the 6th week.
The liver weight at birth is only 5% of total body weight.
Dr M Eladl
35. BLOOD SUPPLY OF THE LIVER
Derived from the coeliac trunk, which is the artery of the foregut.
Dr M Eladl
36. DEVELOPMENT OF THE PANCREAS
The pancreas develops from two buds:
– Ventral bud: Arises from the hepatic diverticulum and gives the
lower part of the head & uncinate process.
– Dorsal bud: Arises from the dorsal aspect of the duodenum and
gives the upper part of the head, neck, body & tail.
Dr M Eladl
37. DEVELOPMENT OF THE PANCREAS
Rotation of the duodenum & unequal growth of its walls leads
to: The ventral pancreas comes to lie below & to the right of
the dorsal pancreas, Which latter fuse with each other as will
as their ducts.
Dr M Eladl
38. DEVELOPMENT OF THE PANCREAS
Rotation of the duodenum & unequal growth of its walls leads
to: The ventral pancreas comes to lie below & to the right of
the dorsal pancreas, Which latter fuse with each other as will
as their ducts.
Dr M Eladl
39. DEVELOPMENT OF PANCREATIC DUCTS
The main pancreatic duct: From
the duct of ventral pancreas
(proximally), distal part of the
duct of dorsal pancreas
(distally).
The accessory pancreatic Duct:
From the proximal part of the
duct of the dorsal pancreas
Dr M Eladl
40. DEVELOPMENT OF PANCREATIC ACINI &
ISLETS
Side branches extend from the
ducts to the surrounding
mesoderm.
Some of them become canalized
pancreatic Acini.
Others separate & not canalized
Islets of Langerhans.
Insulin secretion begins during
the fetal period (10 weeks) and
the total pancreatic insulin
contents also increase with the
fetal age.
The pancreatic connective tissue
stroma and interlobar septa:
from the splanchnic mesoderm.
Dr M Eladl
41. ANOMALIES OF PANCREAS
Annular pancreas:
– Causes:
Growth of a bifid ventral pancreatic bud which fuse with the
dorsal bud forming a ring around the duodenum.
Fixation of ventral lobe to duodenum before rotation.
– Features:
A thin and flat band of pancreatic tissue surrounding the
descending (second) part of the duodenum may cause duodenal
obstruction.
Dr M Eladl
42. ANOMALIES OF PANCREAS
Accessory pancreatic tissue:
– Is often located in the wall of the stomach, duodenum or in the
meckel diveticulum.
Two pancreases:
– Due to failure of union between ventral and dorsal pancreas with
failure of anastomosis of their ducts.
Absence of a part of pancreas (Small pancreas):
– Due to absence of ventral or dorsal pancreas due to failure of
development of one of the pancreatic buds.
Dr M Eladl
