Development Of GI System Flashcards
What are the derivatives of the foregut?
Derivatives of the Midgut
Duodenum distal to the major duodenal papilla,
Jejunum & Ileum; Cecum & Appendix, Ascending colon & right 2/3 of transverse colon
What are the derivatives of the hindgut?
Derivatives of the Hindgut
Left 1/3 of Transverse colon
Descending colon, Sigmoid colon & rectum Anal canal up to the pectinate line
Urinary bladder & most of Urethra
What parts of the viscera are supplied by the celiac artery?
Esophagus Stomach Liver /Gall bladder Pancreas Spleen (developed in dorsal mesogastrium) 1⁄2 Duodenum (superior to the major papilla)
What parts of the of the blood supply of the superior mesenteric ?
Duodenum distal to the major duodenal papilla Jejunum Ileum Cecum /appendix Ascending colon Right 2/3 of transverse colon
What parts of the viscera are supplied by the inferior mesenteric?
Left 1/3 of Transverse colon
Descending colon, Sigmoid colon & rectum
Anal canal up to the pectinate line
Explain formation of the primordial gut
Derived from the dorsal part of umbilical vesicle (yolk sac), within the folds of the embryo
Suspended in the peritoneal cavity by dorsal and ventral mesenteries.
The epithelial lining and glands are derived from yolk sac endoderm
Smooth muscle and connective tissue are derived from splanchnic mesoderm
Neural component derived from the migration of neural crest cells
What happens to the primitive gut after embryonic folding?
After the embryonic folding, intra- embryonic part of the umbilical vesicle (yolk sac) is divided into foregut (within head fold) Midgut & Hindgut (within tail fold)
Omphaloenteric duct (Yolk stalk / vitellointestinal duct) connects midgut to the umbilical vesicle
Describe the epithelial lining of the gut
- Hollow tube
- Epithelial proliferation fills the lumen by 8th week
- Vacuoles then appear
- The process of Recanalization (hollow –solid –hollow) occurs by 10th week
Stenosis: due partial failure of (re) canalization of epithelial proliferation in their lumen
Atresia [e.g. of esophagus / duodenum / biliary tract] due to complete failure of (re)canalization of epithelial proliferation in their lumen
What is the foregut?
Begins at the abdominal esophagus and ends inferior to the major duodenal papilla.
• Esophagus
• Stomach
• Liver /Gall bladder
• Pancreas
• Spleen (developed in dorsal mesogastrium)
• 1⁄2 Duodenum (superior to the major papilla)
What is the blod supply, dranage and lymphatic drainage of the foregut?
Arterial supply : Celiac Trunk
Venous drainage: Portal Venous System
Lymphatic drainage: Celiac Nodes
Describe the anatomy of the stomach
J shaped structure which has 2 openings:
• Cardia
• Plyoric
2 curvatures :
• Greater
• Lesser
2 surfaces (walls)
• Anterior
• Posterior
What are the regions of the stomach?
Cardiac region of the stomach is on the left
Pyloric region of the stomach is to the right
The stomach therefore has its axis running from above left to below right
Describe rhe development of the stomach
Distal part of the foregut shows a fusiform dilatation during 4th week which has :
Right & Left surfaces Anterior & Posterior borders
As the stomach increases in size the posterior border (greater curvature) grows faster than the anterior border (lesser curvature)
- Rotates clockwise around its long axis for 90 degrees.
- Anterior border becomes lesser curvature
- Posterior border becomes greater curvature
Ventral border (lesser curvature) moves to the right; dorsal border (greater curvature) moves to the left
How is rotation impactful in the development of the stomach?
After rotation→long axis of the stomach lies almost transverse to the long axis of the body, left surface becomes anterior wall of the stomach and right surface becomes posterior wall
Summarize development of the stomach
- Positional changes of the stomach are explained by assuming it rotates along a longitudinal and anterior posterior axis
- The stomach rotates 90 degrees clockwise around its longitudinal axis causing the left surface to face anteriorly and its right surface to face posteriorly.
- The vagus nerve initially on the left side of the stomach innervates the anterior wall and the right vagus nerve innervates the posterior wall.
Adult structure : the pyloric part of the stomach moves to the right and upward
the cardiac part of the stomach moves to the left and slightly downwards
• The stomach in its final position has its axis running from above left to below right.
How are dorsal and ventral mesogastrium formed?
Stomach is suspended from the dorsal wall of the abdominal cavity by dorsal mesentery→ dorsal mesogastrium [greater omentum, gastrosplenic ligament & splenorenal ligament]
Ventral mesogastrium attaches stomach & duodenum to the liver & ventral abdominal wall: [falciform ligament & lesser omentum]
What is congenital hypertrophic pyloric stenosis ?
Narrowing (stenosis) of the lumen of pyloric canal caused by hypertrophy of the muscles in the pyloric region
• Incidence : 1/150 male infants, 1/750 female infants
Whst wre the effectsof congenital hypertrophic pyloric stenosis?
- Stomach becomes distended & its contents are expelled with force (projectile vomiting)
- vomitus not bile stained (bile duct opens in 2nd part of duodenum)
Describe the clinical and physiccal presentation of congenital hypertrophic pyloric stenosis
Clinical presentation
•Non bilious projectile vomiting
•Generally starts three weeks after birth or as late as 5 months after birth.
• After the vomitus the infant is hungry and wants to feed again.
Physical examination
Pyloric mass – olive shaped Visible gastric peristaltic wave
Describr the imaging seen on cingenital hypertrophic pyloric stenosis
• Barium swallow shows an abnormal defect in filling in the region of the pyloric sphincter
• Ultrasound –thickening of the pyloric
sphincter.
What is the duodenum?
Duodenum is the first and shortest portion of the small intestine that forms a C shape around the pancreas
What are the parts of the duodenum?
Four parts:
1st (superior) part is horizontal and is referred to as the duodenal bulb
2nd (descending) part is the site of the junction of the foregut and midgut – where the hepatopancreatic duct enters the duodenum through the major duodenal papilla on the posterior medial wall.
3rd (horizontal) part located inferior to the pancreas
4th (ascending) part –it joins duodenojejunal flexure which is suspended from the posterior wall by the Ligament of Treitz- suspensory ligament of the duodenum
Describe the development of the duodenum
- The duodenum develops from the caudal part of the foregut and the cranial part of the midgut
- As the stomach rotates, the duodenum takes on the form of a C-shaped loop and rotates to the right.
- The rotation of the stomach along with the rapid growth of the head of the pancreas, swings the duodenum from the initial midline position to the right side of the abdominal cavity
- The duodenum and head of the pancreas press against the dorsal body wall and become fixed in the retroperitoneal position (secondarily retroperitoneal)
- Epithelial lining proliferates and fills the lumen by 8th week (temporary occlusion of lumen). 10th week the lumen reappears by canalization
What is duodenal srenosis ?
Duodenal Stenosis – partial occlusion of lumen due to incomplete recanalization:
-leads to vomiting which is usually bile stained [if stenosis is distal to the bile duct opening]
What is duodenal atresia?
Duodenal Atresia
– complete occlusion of lumen [failure to recanalize]
-Polyhydramnios
-Vomiting begins immediately after birth
What is the double bubble sign of duodenal atresia?
- Air in the stomach is one bubble
- Air in the proximal duodenum is the
second bubble - Obstruction caused by narrowing of the lumen of the proximal duodenum
Descrbe development of the liver and billiary apparatus
Hepatic diverticulum arises (4th week) from the caudal part of foregut→ extends into the septum transversum
Hepatic diverticulum divides into cranial & caudal parts. Larger cranial part forms the liver; caudal part forms gall bladder & cystic duct
Whhat is the function of the major papilla (hepatopancreatic ampulla)?
Common opening for bile duct and pamcreatic duct
What are the ports of the pamcreas?
The four parts of the pancreas
- Head and uncinate process
- Neck
- Body
- Tail
What is the function of the main pancreatic duct?
The main pancreatic duct traverses the length of the gland to join the common bile duct at the hepatopancreatic ampulla. Together they drain into the duodenum at the major duodenal papilla
Describe the development of pancreas
Pancreas develops from two endodermal buds (ventral & dorsal) from the distal end of the foregut
Dorsal bud appears first [26th day], ventral appears on the 28th day. Rotation and fusion of the buds occur by the 7th week
Pancreatic buds fuse when the duodenum rotates to the right
Dorsal pancreatic bud – forms upper part of the head, body and tail Ventral pancreatic bud – lower part of the head and uncinate process
How does the pamcreatic duct develop?
Main pancreatic duct – develops from proximal part of the duct of ventral bud & distal part of the duct of dorsal bud
Accessory pancreatic duct – proximal part of the duct of dorsal pancreatic bud
What is an annular pancreas?
Annular Pancreas – probably due to bifid ventral pancreatic bud. The ventral pancreatic bud consists of two components that normally fuse and rotate around the duodenum so that they come to lie below the dorsal pancreatic bud.
Occasionally, the right portion of the ventral bud migrates along the normal route, but the left migrates in the opposite direction. A ring of pancreatic tissue encircles the second part of duodenum and causes obstruction
What does the spleen develop from?
The spleen is not an outgrowth of foregut. The spleen is derived from mesenchymal cells between the layers of dorsal mesogastrium (5th week).
Spleen is lobulated in the fetus
