Embryonic Development of Gut Tube

Question 1

Embryonic Folding

Answer 1

• a change in shape resulting from the cranial, lateral, and caudal invagination of the yolk sac roof
• causes the conversion of the flat embryonic disc into an elongated clinder
• yolk sac becomes the gut tube
• by day 26 the midgut opening narrows to form the vitelline duct (which gets incorporated into the umbilical cord)
• also forms the intraembryonic coelom

Question 2

Intraembryonic coelom

Answer 2

• forms at completion of embryonic folding due to the later folds coming together and trapping the extraembryonic coelom
• becomes the peritoneal cavity

Question 3

Regional divisions of the gut tube determined by

Answer 3

blood supply

Note: thoracic foregut supplied by aortic arches

Question 4

Foregut development

Answer 4

• the gut tube in the foregut it connect by two peritoneums (dorsal and ventral)
• as the stomach grows, the dorsal wall grows more rapidly (due to nodal asymmetry) and forms the greater curvature
• differential thinning of the dorsal mesentery results in 90 degree rotation clockwise (dorsal goes from back to the left side)
• liver develops in the ventral mesentery
• spleen develops in the dorsal mesentery

Question 5

End of the lesser omentum

Answer 5

• duodenum becomes stuck against the liver
• end of the foregut
• forms the epiploic foramen which goes into the lesser omental sac

Question 6

Greater omentum significance:

Answer 6

• grows down and sags over the transverse colon, eventually fuses with the transverse mesocolon
• forms a sac with no opening
• formed by double layer peritoneum

Question 7

Length of dorsal mesentery?

Answer 7

-entire gut tube

Question 8

Length of ventral mesentery?

Answer 8

-ventral gut tube

Question 9

lesser sac of the peritoneal cavity

Answer 9

dorsal to the stomach

Question 10

epiploic foramen

Answer 10

connects the two peritoneal compartments

Question 11

cystic diverticulum

Answer 11

• formation of the gall bladder day 26
• a bud forms on the ventral duodenum (caudal to the hepatic diverticulum bud)
• turns into the gallbladder and cystic duct

Question 12

bile duct formation

Answer 12

-cells at the junction of the hepatic and cystic ducts proliferate

Question 13

formation of the pancreas

Answer 13

• day 26 dorsal pancreatic bud forms on dorsal duodenum and grows INTO the dorsal mesentery
• ventral pancreatic bud forms on ventral duodenum (caudal to cystic diverticulum) and grows into the ventral mesentery
• week 5-6 ventral bud migrates to fuse with dorsal
• dorsal duct degenerates leaving the ventral duct at the main connection to duodenum

Question 14

Fixation of duodenum and pancreas

Answer 14

• by week 11
• originally spleen - stomach - liver in straight line ventral to dorsal, then undergo a clockwise rotation
• pancreas stays ventral

Question 15

secondarily retroperitoneal

Answer 15

structures initially suspended from mesenteries become attached to the body wall

IE: duodenum, pancreas, colon

Question 16

Intraperitoneal

Answer 16

structures suspended by mesenteries within the peritoneal cavity

IE: stomach, gall bladder, transverse colon

Question 17

Retroperitoneal

Answer 17

structures attached to the body wall outside of the peritoneal cavity

IE: esophagus, rectum

Question 18

How does fixation to the body wall occur?

Answer 18

-mesentery retracts and then degenerates

Question 19

Midgut development

Answer 19

• midgut is originally continuous with the vitelline duct (yolk stalk)
• cranial part ( ileum) forms a loop that lengthens more rapidly than the abdominal cavity and folds into the primary intestinal loop (weeks 5-6)
• SMA runs between the cranial and caudal portions of the midgut
• Week 6: elongation of midgut forces the intestinal loop to herniate into the umbilicus
• the midgut loop makes a 90 degree turn so cranial is to the right and caudal is to the left
• caudal portion forms the ascending and transverse colon

Question 20

Second rotation of the midgut:

Answer 20

• during week 10 intestinal loop retracts into the abdominal cavity and undergoes 180 rotation
• this rotation causes the ileum to be placed towards the left (the cranial part) and the ascending colon to be towards the right (caudal part) with the transverse above them both
• this rotation also brings the cecum to the right
• by week 11 the ascending colon fixed right to the dorsal body wall
• ileum and transverse remain suspended by mesenteries