Embryology of the GI Tract Flashcards
What happens by week 4
Endodermal tube running thought the centre of the emrbyo is present
What happens to the cloaca
develops into both parts of the urinary system and also for the hind gut
What are the 2 origins of the GI Tract
Endoderm and Visceral mesoderm
What does the endoderm form
Epithelium of mucosa and associated ducts and glands
What does the visceral mesoderm surround
Lamina propria
Muscularis mucosa and muscularis externa
CT of submucosa and External CT
What is the endoderm suspended in a bit of?
The mesoderm
What is the dorsal mesogastrium associated with?
Stomach, duodenum and mesentery proper (largest part of the dorsal mesentery associated with the small intestine
What happens to the dorsal mesogastrium
Moves downwards and forwards to become the greater omentum
How are the mesenteries brought into their final positions
Rotation of different parts of the gut
When is the oesophagus distringuishable by?
End of week 4
What develops in terms of the oesophagus in week 5
Circular muscle
What develops in terms of the oesophagus in week 8
Longitudinal muscle
What does the dilatation indicate at the end of week 4?
The stomach
How is the unusual shape of the stomach brought about
Swelling is not growing at a uniform rate - quicker on the left border. As it grows it starts to undergo a rotation
Where will the original left side of the stomach lie
Anteriorly
Where will the original right side of the stomach lie
Posteriorly
What also rotates at the same time as the stomach
Vagus nerves
Where does the greater curvature move
Slightly inferiorly pointing down
Where does the lesser curvature end up pointing
Slightly downwards
What forms the lesser sac
Growth and rotations of the stomach
What else does the growth and rotation of the stomach cause
The dorsal mesentery to bulge
What forms the greater omentum
Continued growth of the dorsal mesentery
What 2 things form from the ventral mesentery
Lesser omentum and falciform ligament
What 3 parts make up the duodenum and what do they make up
Caudal portion of foregut - parts 1 and 2 of duodenum
Cranial portion of midgut - parts 3 and 4 of duodenum
Duodenal loop is directed to the right due to the rotation of the stomach
Describe the growth of the liver bud
Into the mesoderm of the septum Transversum
What is the duodenum closely associated with
The liver, gall bladder and pancreas
What is important for the formation of the diaphragm
septum transversum
What is the gall bladder associated with
The posterior aspect of the liver
What does the mesoderm of septum transversum give rise to
The development of hepatocytes and the lining of the biliary tree
What does either side of the liver go on to be?
The lesser omentum
Where do the pancreas and the common bile duct form from?
Proliferation of the endoderm
What gives rise to the gall bladder
Diverticulum
Name the two buds of the pancreas
Ventral pancreatic bud and dorsal pancreatic bud
What supplies the dorsal pancreatic bud
The celiac axis
What supplies the ventral pancreatic bud
Superior mesenteric artery
HOw does the ventral pancreatic duct migrate?
It twists so that it lies adjacent to the dorsa pancreatic duct
What happens as the ventral pancreatic duct migrates?
It pulls the common bile duct and the gall bladder closer together
In what direction does the pancreas move?
Clockwise
Where is the spleen derived from?
Mesoderm (not gut tube)
When does the spleen develop
week 5
What is the position of the spleen dictated by
The rotation of the stomach
When does the spleen develop into a lymphatic organ?
Weeks 15-18
What comprises the midgut
Second half of duodenum Jejunum Ileum Caecum and appendix Ascending colon Proximal 2/3rd of transverse colon
What happens at the beginning of week 4 in the midgut
Communicates with the yolk sac along its length
What happens during week 4 in the midgut
Connection with the yolk sac narrows
What happens to the midgut by the end of week 4
Connected to the yolk sac via narrow vitelline duct
What happens in week 5 in terms of the midgut
The midgut has outgrown the embryo and bulges ventrally into the umbilicus
What occupies the majority of the abdominal space
The liver
What direction does the midgut rotate as you look at it
Anticlockwise
What acts as an axis for the rotation to occur around
Superior mesenteric artery
What does the caecal bud develop into and when does this happen
Caecum and the appendix
Week 8
When does re-entry of the midgut into the body cavity occur
Around week 10
What returns first?
Small intestine
Describe the movement of the caecum
It moves back in last and lies below the liver in the Upper right quadrant. It will then move down towards the right ileac fossa.
What is a vitelline cyst
A fibrous plaque
When does the formation of the definitive gut lumen occur?
Weeks 5-9
Why does the lumen of the gut initially become ecluded
The endodermal lining is going to proliferate
