Development of the GI tract Flashcards
What is responsible for holding the organs of the GI tract in place?
- mesentery
The GI tract has intrinsic neurons for motility reflexes - what are intrinsic neurons?
- A type of afferent neurone which connects motor neurons to sensory neurons
The GI tract has vagal and pelvic nerves - what do vagal nerves do?
- A vagal nerve is responsible for carrying signals between the heart, brain and digestive system
What is the parietal peritoneum?
- The lining of the walls of the abdominal cavity
What is the name of the membrane that surrounds the individual organs?
- Visceral peritoneum
Which of the three layers is the GI tract formed from?
- the endoderm
How is the gut tube formed?
- endoderm folds and elevates
- endoderm folds around ventrally
- endoderm fuses ventrally
Where does the splanchnic mesoderm come from?
- the lateral plate mesoderm
What is the endoderm?
- epithelial cell sheet adjacent to the lumen
What is the splanchnic mesothelium?
- connective tissue, smooth muscle and mesothelial layers (mesentery and peritoneum)
What are the three divisions of the primitive gut?
- foregut
- midgut
- hindgut
What is the name of the two membranes at either opening of the primitive gut?
- buccopharyngeal membrane (mouth end)
- cloacal membrane (anal end)
What does the foregut form?
- oesophagus
- stomach
- liver
- gallbladder
- bile ducts
- pancreas
- proximal duodenum
How is the stomach formed during the rotation of the foregut?
- Foregut rotates 90 degrees along the longitudinal axis
- tube budges out to the left side
3 further rotation along the ventrodorsal axis
What is the greater omentum formed from?
- dorsal mesentery
What is the lesser omentum formed from?
- ventral mesentery
What do the ligaments within the omenta do?
- Ligaments are double layers of peritoneum that pass from one organ to another or from an organ to one of the of the abdominal walls
What do these ligaments in the greater omentum link together?
1. gastrophrenic
2. gastrocolic
3. gastrosplenic
4. phrenicosplenic
- stomach > diaphragm
- stomach > transverse colon
- stomach > spleen
- diaphragm > spleen
What do these ligaments in the lesser omentum attach …
1. hepatophrenic
2. hepatogastric
3. hepatoesophageal
4. falciform
- liver > diaphragm
- liver > stomach
- liver > oesophagus
- liver > ventral abdominal wall
As the stomach forms there is also an out pocketing on the ventral side of the gut tube, what does this form?
- gives rise to the ventral pancreatic bud and duct
- gall bladder and liver buds
Once the ventral pancreatic bud, duct, gall bladder and liver buds are formed there is then a clockwise rotation of the proximal duodenum - what does this cause?
- causing the ventral pancreatic bud and duct to come and sit cranial to the dorsal pancreatic bud and duct
- while the liver and gall bladder remain in position
- the ventral and dorsal pancreatic ducts fuse
- bile and pancreatic ducts fuse to drain together at major papilla
How does the spleen form?
- Forms from mesoderm cells in the dorsal mesentery also known as mesogastrium
- its a major haemopoietic organ in the foetus
What are the components of the midgut?
- distal half of the duodenum
- jejunum
- ileum
- caecum
- ascending colon
- proximal half of transverse colon
What is physiological herniation?
- where the midgut grows and loops out of the umbilical cord
The Horse is a hindgut fermenter - describe the equine caecum:
- continues to grow in the embryo
- Adult - 1m length and 30L capacity
Describe the ascending colon in the horse:
- ascending colon continues to grow forming a loop connected by remnants of the dorsal mesentery
Describe the ascending in the ruminant and pig:
- Ascending colon continues to grow forming a spiral
How does the hindgut form (to separate the urogenital tract and the hindgut)?
- Cloacal is common end for hindgut and urogenital tract
- urogenital septum grows towards cloacal membrane
- perineal body separates urogenital and anal membranes
See more on philological herniation in AEU section of book
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