Development of the GI tract Flashcards
When does development of the primitive gut tube begin? What is the internal and external lining derived from?
At the 3rd week:
Internal lining derived from endoderm (future epithelial lining)
External lining derived from splanchnic mesoderm
What does the splanchnic mesoderm give rise to?
Future musculature and visceral peritoneum, the mesentery is also formed from a condensation of this mesoderm
What are the 2 layers of lateral plate mesoderm?
- Splanchnic: covers GI tube
2. Somatic: lines body wall
Which section of the gut tube has a ventral mesentery? What is the ventral mesentery derived from and what else does it give rise to?
The Foregut, derived from the septum transversum; undifferentiated mesoderm that gets carried to its ventral position during longitudinal folding. Also gives rise to the thoracic diaphragm
What forms the greater and lesser peritoneal sacs?
The dorsal and ventral mesenteries divide the foregut cavity into R and L sacs:
- The L sac becomes the greater sac and continues as the bulk of the peritoneal cavity
- The R sac becomes the lesser sac, rotates and ends up lying behind the stomach
What does the Lesser peritoneal sac create?
The greater omentum; fold of visceral peritoneum that hangs down from the stomach
Name 3 functions of the greater omentum
- Physically limits the spread of intraperitoneal infections
- Immune contribution
- Fat deposition
When does the lung bud develop and what does it derive from?
The 4th week from the endoderm
Name 2 conditions that can occur as a result of abnormal positioning of the tracheoesophageal septum
- Proximal blind ended esophagus
2. Tracheoesophageal fistula
Which glands are formed from the ventral and dorsal mesentery?
Ventral: Liver, biliary system, pancreas (uncinate process and inferior head)
Dorsal: pancreas majority (superior head, neck, body, tail)
How does the stomach’s rotation influence positioning of the surrounding nerves?
The VAGUS n follows the stomach’s rotation:
- L vagus: ends up on the anterior surface
- R vagus: ends on the posterior surface
What organs/structures does the foregut give rise to? (6)
- Esophagus
- Stomach
- Pancreas, liver, gallbladder
- Duodenum (proximal to the entrance of the bile duct)
What organs/structures does the midgut give rise to? (7)
- Distal duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 transverse colon
Why does physiological herniation occur?
Since the abdominal cavity is too small to accommodate the rapid simultaneous growth of the liver and the intestinal loop, the intestines must herniate into the umbilicus temporarily
How does the rotation of the stomach influence the duodenum?
As the stomach rotates the duodenum grows in a C shaped loop, gets pushed right and then against the posterior abdominal wall (some parts are retroperitoneal)
Why is the descent of the cecal bud important and what happens if this fails to occur?
Ensures the ascending colon lengthens, without this descent you may have a sub-hepatic cecum
Name 3 things that can occur as a result of a persisting vitelline duct
- Cyst that can become inflamed
- Fistula (contents can dribble out)
- Meckel’s diverticulum: a persisting pouch of endoderm
What are the potential consequences of having a Meckel’s diverticulum?
The mucosa can contain gastric and pancreatic tissue that can produce cells secreting acid and/or proteolytic enzymes. If the secretions are high enough it can cause an ulceration
What is the rule of 2’s in Meckel’s diverticulum? (5 things)
2% population, 2 feet from the ileocecal valve, 2 inches long, usually detected in under 2s, 2:1 male: female
What does Meckel’s diverticulum mimic?
Early stages of appendicitis
What is recanalization? What can happen if it’s unsuccessful? Where is it most common?
Cell growth can become so rapid that the lumen may become partially or completely obliterated - posing the need to restore the lumen
If it’s unsuccessful can lead to:
- Stenosis; narrowing of the lumen
- Atresia; lumen obliterated `
What is the most common cause of Upper and lower duodenum atresia?
Upper: failure of recanalization
Lower: vascular accident
What is gastroschisis?
A defect in the anterior abdominal wall (fails to close), gut tube and derivatives are outside body cavity
What is omphalocele?
Persistence of a physiological herniation: SI comes out of the umbilicus
