Gastro-intestinal Module
Dr. Gamal Taha
Assistant Professor of Anatomy & Embryology
GIT
Embryology
The Primitive Gut
◼ The primitive gut forms during the 4th week of
gestation when the flat embryonic disc folds in
median and horizontal planes to form a tubular
structure that incorporates part of the yolk sac into
the embryo
◼ Ventral folding of cranial and caudal ends (head
and tail folds) form the foregut and the hindgut
◼ Ventral folding of lateral sides forms the midgut
◼ The stroma (connective tissue) for the
glands, muscle, connective tissue, and
peritoneal components of the wall of
the gut, ALL are derived from
visceral mesoderm.
Normal Embryology
◼ Endoderm
◼ Epithelial lining and glands
◼ Mesoderm
◼ Lamina propria, muscularis mucosa,
submucosa, muscularis externa and serosa
◼ Ectoderm
◼ Enteric nervous system and posterior luminal
digestive structures
Normal Embryology
◼ Primitive Gut Tube
◼ Incorporation of the yolk sac during
craniocaudal and lateral folding of the
embryo.
◼ Foregut
◼ Midgut
◼ Hindgut
Canalization
◼ Canalization
◼ Week 5 - Endoderm portion of GI tract
proliferates
◼ Week 6 - Occlusion of the lumen
◼ Week 8 - Recanalization due to cell
degeneration
◼ Abnormalities in this process
◼ Stenosis/Atresia
◼ Duplications
The Derivatives of the Gut Region
◼ FOREGUT
1. Trachea & respiratory tract
2. Lungs
3. Esophagus
4. Stomach
5. Liver Gallbladder & bile ducts
6. Pancreas (dorsal & ventral)
7. Upper duodenum
The Derivatives of the Gut Region
◼ MIDGUT
1. Lower duodenum
2. Jejunum
3. Ileum
4. Caecum
5. Appendix
6. Ascending colon
7. Proximal transverse 2/3 colon
The Derivatives of the Gut Region
◼ HINDGUT
1. Distal 2/3 transverse colon
2. Descending colon
3. Sigmoid colon
4. Rectum
5. Upper anal canal
6. Urogenital sinus
The Derivatives of the Gut Region
◼ BASED ON THE ARTERIAL SUPPLY:
◼ Foregut derivatives in the abdomen are
supplied by branches of the celiac artery
◼ Midgut derivatives are supplied by branches
of the superior mesenteric artery
◼ Hindgut derivatives are supplied by
branches of the inferior mesenteric
artery
Foregut
◼ Esophagus
The tracheoesophageal bud, at
the ventral side of the primitive
esophagus, approximately at 4
weeks old, develops a septum
that divides foregut into the
esophagus and trachea
◼ Clinical Correlation
◼ Esophageal atresia
◼ Tracheoesophageal fistula
◼ The tracheoesophageal septum gradually
partitions this diverticulum from the dorsal part of
the foregut.
◼ In this manner, the foregut divides into:
➢ A ventral portion, the respiratory primordium,
and
➢ A dorsal portion, the esophagus
The Esophagus
◼ At first, the Esophagus is short (A), but
with descent of the heart and lungs, it
lengthens rapidly (B).
Clinical Correlation
◼ Esophageal atresia
◼ Usually is accompanied by a
tracheoesophageal fistula, in which case gut
contents can be Aspirated into the lungs after
birth causing inflammation (pneumonitis) or
even infection (Pneumonia).
◼ Postnatally,
the child will regurgitate
IMMEDIATELY upon starting breast feeding
Clinical Correlation
◼ Occurs in 1 in ~ 3000 births
◼ Highest incidence in Caucasians
◼ 50% have associated congenital anomalies
◼ Diagnosis
◼ Prenatal Ultrasound – polyhydramnios
◼ CXR – absence of gastric bubble, tracheal deviation
◼ CT
◼ Feeding difficulties with respiratory symptoms
◼ Etiology
◼ Canalization defect
◼ Defect with tracheoesophageal septum development
Clinical Correlation
Clinical Correlation
Esophageal stenosis
◼ It occurs when the esophagus fails to recanalize also
typically associated with polyhydramnios prenatally.
Postnatally, the child will regurgitate frequently upon
feeding. However, there is usually NOT a
tracheoesophageal fistula, so the lungs will usually NOT
be congested.
Congenital hiatal hernia
◼ It occurs when the esophagus fails to grow adequately
in length. As a result, the esophagus is too short and
therefore pulls the cardiac stomach into the esophageal
hiatus in the diaphragm. The resulting compromised
structure of the hiatus can allow other gut to herniate
Foregut
◼ Stomach
A fusiform dilation in
the foregut occurring
during the 4th week.
90 degree clockwise
rotation, creates the
lesser peritoneal sac
just behind the
stomach.
The Vagus nerves follow
Stomach
◼
this rotation which is
how the left Vagus
becomes anterior and
the right becomes
posterior.
◼ Differential growth
occurs to establish the
greater and lesser
curvatures
◼ Unlike other parts of the
gut tube, the dorsal AND
ventral mesenteries are
retained to become the
greater and lesser
omenta, respectively
◼ As this process continues in the fifth
week of development, the Spleen
primordium appears as a mesodermal
proliferation between the two leaves of
the dorsal mesogastrium.
Spleen
◼ The Spleen, which remains
intraperitoneal, is then connected:
To the body wall in the region of the left
kidney by the lienorenal ligament and
to the stomach by the gastrosplenic
ligament
As a result of rotation of the stomach
the dorsal mesogastrium bulges
down.
It continues to
grow down and
forms a double-
layered sac
extending over the
transverse colon
and small intestinal
loops like an
apron.
◼ The greater omentum;
later, Fuses its layers,
to form a single sheet
hanging from the greater
curvature of the stomach.
◼ The posterior layer of the
greater omentum also
fuses with the
mesentery of the
transverse colon.
Clinical Correlation
◼ Pyloric Stenosis
◼ Rather common malformation:
present in 0.5% - 0.1% of infants,
more in males
◼ Characterized by very forceful (aka
“projectile”), non-bilious vomiting
~1hr. After feeding (when pyloric
emptying would occur).
NOTE: the presence of bile would
indicate POST-duodenal blockage of
some sort.
Clinical Correlation
Pyloric Stenosis
◼ Hypertrophied sphincter can
often be palpated as a spherical
nodule; peristalsis of the
sphincter seen/felt under the
skin.
◼ Stenosis is due to over
proliferation / hypertrophy of
pyloric sphincter… NOT an error
in re-canalization.
◼ Treated by sphincterotomy
Foregut
◼ Liver – Develops from an
endodermal outgrowth at
cranioventral portion of
the foregut
(hepatobiliary
diverticulum) by the
middle of the 3rd week
◼ Hepatocytes invade the
mesoderm of the septum
transversum.
The Liver
The Liver
◼ Hepatic cells (hepatoblasts) migrate into the
Lightly packed part of the septum
transversum.
◼ The migrating cells are both hematopoietic
and endothelial precursors.
◼ The hepatic cells surround the endothelial
precursor cells, vitelline veins, to form the
hepatic sinusoids.
The Liver
◼ Hematopoietic cells
◼ Kupffer cells
◼ Connective tissue cells are derived from mesoderm of
the Septum Transversum
◼ This portion of the septum, which consists of densely
packed mesoderm, will form the central tendon of
the diaphragm.
◼ The surface of the liver that is in contact with the
future diaphragm is never covered by peritoneum; it is
the bare area of the liver.
Gallbladder and Bile Ducts
◼ Cystic diverticulum
develops from the
proximal part of the
hepatobiliary bud
into gallbladder and
cystic duct.
Pancreas
◼ Develops from 2 pancreatic buds between
(weeks 4-5).
◼ Ventral pancreatic bud forms the uncinate
process and the head of the pancreas.
◼ The larger dorsal pancreatic bud forms
the remaining head, body and tail.
Pancreas
◼ When the duodenum rotates to the right and
becomes C-shaped, the ventral pancreatic
bud moves dorsally in a manner leading to
the shifting of the entrance of the bile duct.
◼ Finally, the ventral bud comes to lie
immediately below and behind the
dorsal bud.
◼ Later, the parenchyma and the duct systems
of the dorsal and ventral pancreatic buds fuse.
Pancreas
◼ The ventral pancreatic bud
rotates clockwise with the
rotation of the duodenum.
During 7th week the 2 buds
fuse.
◼ Within each bud, the
endoderm develops into
branched tubules attached to
secretory acini (the exocrine
pancreas).
Pancreas
◼ The endocrine pancreas
(islets of Langerhans)
arise from stem cells at
the duct branch points
that then develop into
discrete islands of
vascularized endocrine
tissue within the
pancreas
Clinical Correlation
◼ Errors in the fusion
process can result
in an annular
pancreas that
wraps around the
duodenum, which
can cause
obstruction
(Bilious
Vomiting)
Clinical Correlation
◼ Also, since the dorsal and ventral
pancreas arise by different
mechanisms, it’s possible that one or
the other may be absent in the adult.
◼ For further inquiries PLZ feel
free to contact at any time
through email
gamaltaha@med.asu.edu.eg
