Gi Flashcards
During which weeks is the primitive gut tube formed?
The primitive gut tube is formed during Week 3 and 4.
At what week does the liver form? Where from?
Liver forms at WEEK 3 from a ventral outgrowth of foregut as an out pocketing of the future duodenum. Hepatic diverticulum
How is the primitive gut tube formed?
It is formed via craniocaudal and lateral folding of the embryo.
The visceral and parietal mesoderm give rise to what?
Gives rise to visceral and parietal peritoneum.
How is the primitive gut tube suspended?
Suspended from the anterior abdominal wall by dorsal mesentery.
What dies the ventral mesentery form?
Forms lesser omentum and falciform ligament.
What do the vitelline arteries give rise to?
Th give rise to the branches of the GI tract
At what week does the stomach become first apparent?
Stomach becomes apparent at WEEK 4 as fusiform dilatation of the foregut.
During which weeks does the oesphagus lengthen?
Oesophagus lengthens during Weeks 4-7
If the endoderm doesn’t proliferate fast enough what can happen?
Oesophageal atresia can occur which prevents the fetus from swallowing amniotic fluid, returning it to the mother (polyhydramnios)
During week 5 what happens to the midgut?
The midgut rapidly expands to form the primary intestinal loop and the liver grows.
At what week does the pancreas and spleen develop/ form?
The pancreas forms at week 5. The spleen also develops during week 5.
During weeks 7-8 what happens to the stomach?
Rotates around 2 axes. 90 degree rotation around craniocaudal axis causes lesser curvature to move from ventral to right.
Greater curvature moves from dorsal to left.
Also slight ventral dorsal movement so greater curvature faces slightly caudally
As the stomach rotates what is formed?
A space is left behind it which forms the lesser peritoneal sac.
The primary intestinal loop has two limbs, what are they?
Cranial and caudal limbs.
Cranial forms distal duodenum, jejunum, and proximal ileum.
Caudal: distal ileum, caecum, appendix, ascending and proximal 2/3 of transverse colon.
How and when does the midgut become herniated?
Week 6 due to rapid growth of the liver
During week 6 how does the midgut rotate?
The midgut rotates 90 degrees anti clockwise around the SMA as hernination occurs.
Brings cranial limb right and caudal limb left.
When does the small ventral pancreatic bud and larger dorsal pancreatic bud fuse?
During week 6.
What does the dorsal bud of pancreas give rise to?
Head, body and tail. Ventral forms uncinate.
When does the midgut return to the abdomen after herniation?
In week 10. The midgut returns and rotates a further 180 degrees anticlockwise.
Brings proximal jejunal loops to left and caecum lies inferior to liver.
During which week does bile production begin?
Week 12.
During which week do gastric cells differentiate?
Week 9.
During which week is the veniform appendix formed?
Week 10 as the midgut rotates 180 degrees anti clockwise. Caecum develops a wormlike diverticulum.
Which week does the midgut finally completely return to the abdomen?
Week 11 after a 270 degree total rotation anticlockwise.
After the midgut has returned, what happens to the caecum?
Caecum descends from below the liver to right iliac fossa.
This pulls the ascending and transverse colon into place.
During weeks 4-6 a layer of mesoderm extends caudally. How does this contribute to the formation of the hind gut?
As it extends caudally, it separates the urogenital sinus and anorectal canal to form the urorectal septum.
What will the ventral part of cloaca (urogenital sinus) form?
Urogenital sinus will form the bladder, pelvic urethra, penile urethra and caudal part of vagina.
When does the cloacal membrane rupture and what does it create?
In week 7 it ruptures to create the anal opening and a ventral opening for the urgent tail sinus.
What does the tip of the urorectal septum form?
The urorectal septum lies between anal opening and opening for urogenital sinus to form perineal body.
What is the anal canal formed from?
Upper 2/3 - from hindgut. Endoderm
Lower 1/3 - proctodeum (anal pit)
Formation of gut lumen. When does the gut tube become occluded?
Week 6 as endoderm derived epithelial lining proliferates.
Apoptosis from week 6-8 create vacuoles.
When do the vacuoles in the gut lumen recanalise the gut tube?
By week 9
