1. EMBRYOLOGY OF PANCREAS & SMALL INTESTINE
Prof. Mujahid Khan
اسم ورقم المقرر – Course Name and No.
5/2/2019

2. Primordial Gut
At the beginning of the 4th week the primordial gut is closed at its cranial end by the oropharyngeal membrane
Primordial gut forms during the 4th week as the head, tail and lateral folds incorporate the dorsal part of the yolk sac into the embryo

4. Primordial Gut
The endoderm of primordial gut gives rise to most of the epithelium and glands of the digestive tract
The epithelium at the cranial (upper) and caudal (lower) ends of the tract is derived from ectoderm of the stomodeum and proctodeum

6. Foregut The derivatives of foregut are:
The primordial pharynx and its derivatives
The lower respiratory system
The esophagus and stomach
The duodenum, proximal to the opening of the bile duct
The liver, biliary apparatus and pancreas

7. Stomach
During middle of the 4th week a slight dilation indicates the site of the stomach primordium
It first appears as a fusiform enlargement of the caudal (lower) part of the foregut
It initially oriented in the midian plane
It soon enlarges and broadens ventrodorsally
During the next 2 weeks its dorsal border grows faster than the ventral border
This demarcates the greater curvature of the stomach

9. Rotation of Stomach
As the stomach enlarges and acquires the adult shape it slowly rotates 90 degrees in a clockwise direction around its longitudinal axis

10. Effects of Rotation
The ventral border (lesser curvature) moves to the right
The dorsal border (greater curvature) moves to the left
The original left side becomes the ventral surface
The original right side becomes the dorsal surface

11. Effects of Rotation
Before rotation the cranial and caudal ends of the stomach are in median plane
After rotation the stomach assumes its final position with its long axis almost transverse to the long axis of the body
Rotation explains why the left vagus nerve supplies the anterior wall of the adult stomach and right vagus nerve innervates its posterior wall

12. Duodenum
Early in the 4th week the duodenum begins to develop from the caudal (lower) part of the foregut and cranial (upper) part of the midgut
The junction of the two parts of the duodenum is just distal to the origin of the bile duct
As the stomach rotates, the duodenal loop rotates to the right and comes to lie retroperitoneally

13. Duodenum
Because it is derived from the foregut and midgut, it is supplied by the branches of the celiac and superior mesenteric arteries
During the 5th and 6th weeks, the lumen of the duodenum is temporarily obliterated by proliferation of its epithelial cells
It normally recanalized by the end of the embryonic period

14. Ventral Mesentery This thin double layered membrane gives rise to:
The lesser omentum, passing from the liver to the lesser curvature of the stomach called hepatogastric ligament
From the liver to the duodenum the hepatoduodenal ligament
Falciform ligament extending from the liver to the ventral abdominal wall

15. Pancreas
It develops between the layers of the mesentery from dorsal and ventral pancreatic buds of endodermal cells
These buds arise from the caudal (lower) part of the foregut
Most of the pancreas is derived from the dorsal pancreatic bud

17. Pancreas
As the duodenum rotates to the right and becomes C-shaped, the ventral pancreatic bud is carried dorsally with the bile duct
It soon lies posterior to the dorsal pancreatic bud and later fuses with it
The ventral pancreatic bud forms the uncinate process and part of the head of the pancreas
As the stomach, duodenum and ventral mesentery rotate, the pancreas comes to lie along the dorsal abdominal wall

18. اسم ورقم المقرر – Course Name and No.
5/2/2019

19. Pancreas
The main pancreatic duct forms from the duct of the ventral bud and the distal part of the duct of the dorsal bud
The proximal part of the duct of the dorsal bud often persists as an accessory pancreatic duct
The two ducts often communicate with each other
In about 9% of people, the pancreatic ducts fail to fuse

20. Midgut The derivatives of the midgut are:
The small intestine including most of the duodenum
The cecum, appendix, ascending colon and the right half to two-thirds of the transverse colon

21. Midgut
Midgut derivatives are supplied by the superior mesenteric artery
The midgut loop is suspended from the dorsal abdominal wall by an elongated mesentery
As the midgut elongates, it forms a ventral U-shaped loop of gut, the midgut loop
It projects into the proximal part of the umbilical cord

23. Midgut
This movement of the intestine is a physiological umbilical herniation
It occurs at the beginning of the 6th week
The midgut loop communicates with the yolk sac through the narrow yolk stalk until the 10th week

25. Midgut
Umbilical herniation occurs because there is not enough room in the abdomen for the rapidly growing midgut
The shortage of space is caused mainly by the relatively large liver and two sets of kidneys during this stage of development
The midgut loop has a cranial limb and a caudal limb
Yolk stalk is attached to the apex of the midgut loop where the two limbs join

27. Midgut The cranial limb grows rapidly and forms small intestinal loops
The caudal limb undergoes very little change except for development of cecal diverticulum which is a primordium of the cecum and appendix

29. Rotation of Midgut Loop
While it is in the umbilical cord the midgut loop rotates 90º counterclockwise around the axis of superior mesenteric artery
This brings cranial limb to the right and the caudal limb to the left
During rotation the midgut elongates and forms intestinal loops e.g. Jejunum and ileum

31. Return of Midgut Loop to Abdomen
During the 10th week the intestines return to the abdomen
What causes the return of the intestine is not clearly known
The decrease in the size of the liver and kidneys and the enlargement of the abdominal cavity are important factors
This process is called reduction of the physiological midgut hernia

33. Return of Midgut Loop to Abdomen
The small intestine formed from cranial limb returns first
It passes posterior to the superior mesenteric artery and occupies the central part of the abdomen
As the large intestine returns, it undergoes further 180º counterclockwise rotation
Later, large intestine comes to occupy the right side of the abdomen

34. Umbilical Hernia
When the intestines return back to the abdominal cavity during the 10th week and then herniate through an imperfectly closed umbilicus, an umbilical hernia forms
Hernia reaches its maximum size at the end of the first month after birth

35. Umbilical Hernia It usually ranges from 1 to 5 cm
The defect through which the hernia occurs is the linea alba
Hernia protrudes during crying, straining, or coughing
It can easily be reduced through the fibrous ring at the umbilicus
Surgery is not usually performed until it persists to the age of 3 to 5 years

36. Meckel Diverticulum
This outpouching is one of the most common anomalies of the digestive tract
This congenital ileal diverticulum occurs in 2 to 4% of people
3 to 5 times more prevalent in males than females
It sometimes becomes inflamed and causes symptoms that mimic appendicitis

38. THE END