Gastrointestinal tract Flashcards
What leads to the formation of the endodermal gut tube?
Embryonic folding (amnion folds around the embryo)
Change in shape of the yolk sac
What is the coelomic cavity, when does it form?
The space between the gut tube and somatic mesoderm
Forms in folding of the embryo as parietal mesoderm fuses
What is the cavity outside of the coelomic cavity?
Amniotic cavity
What mesoderm makes up the gut tube?
Splanchnic (visceral) mesoderm
What joins to the visceral/splanchnic mesoderm to the parietal mesoderm?
Dorsal mesentery
What is the origin of the epithelial lining of the gut tube?
Endoderm
At the rostral/caudal ends of the gut tube, what does the endoderm interface with, what are these areas called?
Ectoderm
Buccopharyngeal membrane (rostral)
Cloacal membrane (caudal)
Is there a ventral mesentery? What level at?
Yes
At the level of the stomach and liver
What develops within the ventral mesentery?
The liver
What does the ventral mesentery end up as?
The lesser omentum and falciform ligament
Describe the blood supply to each gut region?
The foregut, is supplied by the coeliac artery.
The midgut, is supplied by the superior mesenteric artery.
The hindgut, is supplied by the inferior mesenteric artery.
What mesentery does the stomach have?
Both dorsal and ventral
What is the initial shape of the stomach?
Fusiform
What is the movement of the stomach as it enlarges?
Rotates 90 degrees
What does the rotation of the stomach do the vagus nerves?
Moves the left vagus nerve anterior and right vagus posterior
What does the second rotation of the stomach achieve?
Upper cardiac part moves to the left side and the pyloric lower part moves to the right
What is the lesser sack continuous with the greater sack through?
Epiploic foramen
What does the dorsal mesentery become at the stomach?
Greater omentum
What does the liver form from?
Diverticulum from the gut tube
Where does the initial liver bud grow into?
Mesoderm of the septum transversum
What does the mesoderm pulled along by the liver bud form?
Lesser omentum and falciform ligament
What does the caudal part of the liver diverticulum form?
Gall bladder
What happens to the cranial part of the liver diverticulum?
Undergoes repeated branching to form first a major left and right branch and then a series of smaller branches to generate the liver cords of hepatocytes and vascular sinuses.
What lies between developing hepatocytes?
Bile cannaliculi
What is the remnants of the umbilical vein?
Ligamentum teres
What is the remnants of the ductus venosus?
Ligamentum venosum
Where are the ligamentum teres and ligamentum venosum found?
Within the falciform ligament
What does the pancreas develop from?
Two buds
What are the two pancreas buds?
A ventral bud from the liver diverticulum and a dorsal bud.
What pancreas bud comes from the liver diverticulum?
Ventral
How does the pancreas form one organ?
As the gut rotates, the ventral bud moves behind the duodenum and fuses with the dorsal bud to form the hook-shaped pancreas.
What parts of the adult pancreas do the dorsal and ventral buds form?
The ventral bud forms the uncinate process of the adult pancreas, while the dorsal bud forms most of the head body and tail.
Is the pancreas intra or retroperitoneal?
Pancreas is secondarily retroperitoneal except for the tail which is intraperitoneal
Why is the pancreas (mainly) secondarily retroperitoneal?
Structures initially were suspended in mesentery and later migrated behind the peritoneum during development
Mesentery of pancreas fuses with the posterior abdominal wall
What is hypothesised to cause gut rotations?
Nodal flow asymmetry - asymmetric localisation of nodal gene expression and consequent asymmetric development of the body.
What suspends the midgut?
Dorsal mesentery
What means the gut has to rotate around an axis?
It is fixed by the superior mesenteric artery and vitelline duct
What does growth of the gut tube lead to?
Growth exceed the capacity of the cavity it herniates through the anterior abdominal wall to form a membranous sac of gut in the umbilical trunk.
What causes formation of jejunal-ilial folds?
Rapid elongation
As the gut herniates what does it do?
Rotates 90 degrees anti-clockwise
What happens to the herniated, rotated gut tube after some time?
Retracts back into abdominal cavity
When the gut tube returns to the abdominal cavity, what does it do?
Rotates a further 180 degrees anti-clockwise
What is the total rotation of the gut tube (size and direction)?
270 degrees anti-clockwise
What does the hindgut consist of?
Distal 1/3 of transverse colon
Descending colon, sigmoid colon and rectum
Superior part of anal canal
Is the colon retro/intraperitoneal, how?
Secondarily retroperitoneal, mesentery fuses with posterior abdominal wall
How is the urogenital system separated from the gut?
Urorectal septum grows between the two cavities.
What does splanchnic mesoderm form?
Visceral peritoneum (surrounds gut), muscle and connective tissue around lining
What does somatic mesoderm form?
Parietal peritoneum (lines abdominal cavity) connective tissue of abdominal wall
What is a hiatal hernia?
Hiatal hernia is a type of hernia in which abdominal organs (typically the stomach) slip through the diaphragm into the middle compartment of the chest
What does intraembryonic coelom between 2 layers of mesoderm form?
Peritoneal cavity (splits lateral plate mesoderm into 2 layers)
Gut diverticula undergo branching morphogenesis to form the ….
Liver, pancreas and lungs
