2. Derivatives of foregut
• The foregut are portion of the fetus that
extend from the buccopharyngeal membrane
(definitive mouth) to the definitive half of the
second part of the duodenum
• It is formed from the endodermal germ layer
by cephalo-caudal and lateral folding of the
embryo at about three weeks of IU live
3. Derivatives of foregut
•
•
•
•
Cranial fold
foregut
Caudal fold
Hindgut
Lateral fold
Midgut
Foregut appeared initial as a tubular
diverticulum cranial to the yolk sac and is
located dorsal to the pericardial cavity and
septum transversum
4. Derivatives of foregut
• The blind cranial end extremity of the foregut
forms the endodermal layer of the
buccopharyngeal membrane which separate it
from the stomatodeum (ectoderm)
• At about 21days (20 somites) the membrane
ruptures allowing communication btw the
foregut and the amniotic fluid
5. Derivatives of foregut
• Foregut derivatives are divided into
– cranial portion –bounded laterally by the branchial
arches
– Caudal portion- bounded by the pericardioperitoneal canal which later become the pleural
and peritoneal cavity
6. Cranial portion of the Foregut
• The cranial portion of the foregut forms the
pharyngeal pouches and their derivatives
• The first pharyngeal pouch
Eustachian
tube
• The second pharyngeal pouch Tonsillar
fossa
• The third pharyngeal pouch
Inferior
parathyroid pouch and the thymus
7. Cranial portion of the Foregut
• The fourth pharyngeal pouch
Superior
parathyroid gland
• Other derivatives of the cranial portion
include
– Thyroid gland
– Respiratory tree
– Pharynx
8. Respiratory system
• The respiratory tree arises as a median ventral
diverticulum called laryngotracheal
diverticulum of the foregut.
• The diverticulum appears about the 25
somites (4 weeks IU live) and is in direct
continuation with the definitive esophagus
• Two longitudinal ridges which later fuses
craniocaudally separate the respiratory system
from the esophagus
9. Respiratory system
• Failure of the fusion of the ridges lead to
tracheoesophageal fistula
• The diverticulum elongate in the midline with
the caudal end dividing into two lateral
outpouching
• The midline cranial portion forms the larynx
and tracheal
– Note the cartilages and the muscles are from the
mesoderm
10. Respiratory system
• The lateral buds continue to divides even after
birth giving rise to bronchi etc
11. Caudal portion of the foregut
• Caudal portion of the foregut give rise to he
esophagus, stomach, liver, biliary system and
pancreas.
• All these structures appear during weeks 4-5.
12. Esophagus
• The development of the esophagus is
complicated by the outpocketing of of the
respiratory diverticulum or lung buds from
the ventral wall. Essential to normal
development is the completion of the
esophagotracheal septum which makes the
espophagus, the pathway for food, distinct
from the trachea, or pathway for air. The
esophagus lengthens during the 5th week as
the heart descends.
13. Esophagus
• The wall of the upper esophagus
skeletal
muscle from the 6th pharyngeal arch
• The wall of the lower esophagus
smooth
muscle from splanchnic mesoderm
• The dorsal mesenterty of the esophagus, the
mesoesophagus becomes incorporated into the
diaphragm and is thus, obliterated in the adult.
14. Stomach
• The stomach appears as a dilation of the
foregut caudal to the esophagus during the
fourth week of development.
• The stomach evolves by two rotations along a
longitudinal and anteroposterior axis.
15. Stomach
• The longitudinal rotation of the stomach
involves a 90° clockwise rotation resulting in
the right side of the stomach becoming
posteriorly oriented and the left side of the
stomach facing anteriorly. This explains why
the left vagus nerve innervates the anterior
wall of the stomach and the right vagus nerve
innervates the posterior wall of the stomach
in the adult.
16. Stomach
• During this rotation one side of the stomach
grows faster than the other forming the
greater and lesser curvatures of the stomach.
The stomach subsequently rocks on its
longitudinal axis, causing the pylorus to shift
to right and the cardiac orifice to shift to the
left.
17. Stomach
• The stomach, like the rest of the developing gut
has a dorsal mesentery (dorsal mesogastrium)
and an additional ventral mesentery, (the ventral
mesogastrium), formed from the septum
transversum.
• The rotation and uneven growth of the stomach
pull the dorsal mesogastrium to the left, creating
a subdivision of the peritoneal cavity, the
omental bursa, posterior to the stomach and
between the stomach and the posterior body
wall.
18. Stomach
• The dorsal mesogastrium grows in a caudal
direction as the stomach rotates along its
anterioposterior axis and forms the greater
omentum, a double layered apron over the
transverse colon.
• The ventral mesogastrium is separated into parts
by the formation of the liver. The portion which
attaches to the lesser curvature of the stomach
and to the liver is the lesser omentum.
19. Duodenum
• The duodenum forms at the junction of the
foregut and midgut.
• The more cranial (foregut) portion of the
duodenum gives rise to the hepatic
diverticulum, biliary system and pancreatic
diverticula.
• As the stomach rotates the duodenum also
rotates and comes to lie against the dorsal
body wall.
20. Duodenum
• The mesoduodenum fuses with the back body
wall leaving the main portion of the
duodenum secondarily retroperitoneal.
• The superior and descending portions of the
duodenum are considered part of the foregut
and the horizontal and ascending portions of
the duodenum are considered part of the
midgut.
21. Liver and Gallbladder
• The hepatic diverticulum or liver bud penetrates
ventrally from the duodenum into the
mesodermal septum transversum at 3 weeks.
• The hepatic diverticulum narrows to form the bile
duct which gives rise to a gallbladder.
• As the liver grows, it comes to occupy the
abdominal cavity and lies suspended by
mesentery: anteriorly, the falciform ligament and
posterolaterally, the lesser omentum.
22. Liver and Gallbladder
• The portal vein, hepatic artery, and common bile
duct reach the liver through the caudal margin of
the lesser omentum.
• Growth of the liver downward from the septum
transversum displaces the stomach to the left.
Most of the liver becomes covered with
peritoneum, but a small portion, the bare area of
the adult liver, never completely detaches from
the septum transversum. Duplication of the
gallbladder can occur.
23. Pancreas
• Two pancreatic diverticula develop from the
foregut in the region of the duodenum, one in
the ventral mesentery (ventral mesogastrium)
and one in the dorsal mesentery
(mesoduodenum).
• Due to rotation of the duodenum, the two buds
come to lie together and fuse.
• The pancreas is pushed against the back wall with
the duodenum and also becomes secondarily
retroperitoneal.
24. Pancreas
• The duct system of the ventral pancreas and most
of the dorsal pancreas persists as the main
pancreatic duct.
• A portion of the dorsal pancreatic duct enters the
duodenum separately as the accessory pancreatic
duct.
• In some cases, the ventral pancreas may enclose
the second part of the duodenum, obstructing it.
This condition is termed annular pancreas.
25. Spleen
• Note: The spleen is not a derivative of the foregut
. It develops, however, as a mesodermal
proliferation between the two leaves of dorsal
mesogastrium.
• As the stomach rotates and the liver enlarges, the
spleen becomes situated in the left
hypochondriac quadrant. It is attached to the
back wall by the lienorenal ligament and to the
stomach anteriorly by the gastrosplenic ligament.
These ligaments form the lateral wall of the
omental bursa in the adult.
26. Blood supply of the foregut
• Branches from the aortic arches and branches
from the descending thoracic aorta above the
developing diaphragm
• Celiac artery supplies the foregut below the
diaphragm
