Embryology Flashcards
Which germ layer gives rise to the epithilium of the GI tract and associated ducts and glands?
Endoderm
Which germ layer gives rise to the lamina propria, muscularis mucosae, muscularis externa, the connective tissue of submucosa and adventicia?
Visceral mesoderm
What is formed from the ventral mesentaries?
Lesser omentum and the falciform ligament
What is formed form the dorsal mesentries?
Doral mesogastrium, dorsal mesoduodenum, Dorsal mesocolon
What is the vitelline duct?
long narrow tube that joins the yolk sac to the midgut lumen
What does the cloaca form?
Some of the hind gut and urogenital system
What causes the mesenteries to come to there final positions?
Rotation of different parts of the gut
When is the oesophagus distinguishable?
When does the circular and longitudinal muscle develop?
Distinguishable by the end of week 4
Circular muscle develops week 5
Longitudinal muscle develops week 8
How does the stomach develop?
End of week 4 = dilation of the caudal part of the foregut
The dorsal boarder grows more rapidly than the ventral boader producing greater and lesser curvature.
90 degree rotation about both longitudinal and anterior posterior axes.
What creates the lesser sac causing the dorsal mesentery to bulge?
Growth and rotation of the stomach
What forms the greater omentum?
Continued growth of the dorsal mesentary
What forms the horizontal (1) and descending (2) parts of the duodenum?
Caudal portion of the foregut
What forms the horizontal (3) and ascending (4) parts to the duodenum?
Cranial part of the mid gut
Why is the duodenal loop directed to the right?
Rotation of the stomach
How does the liver form?
Liver bud grows into the mesoderm of Septum Transversum.
What is contained within the sepum transversum?
Haematopioetic cells
Kupffer cells
Connective tissue
What germ layer forms the liver cells and the lining of the billary tree?
Endoderm
How does the pancreas form?
From a ventral and dorsal ancreatic bud which grow and then between 32 and 35 days the ventral pancreatic bud rotates to join the two
The pancreas develops intraperitoneal and then upon rotation becomes retroperitoneal. T or F?
True
What is annular pancreas (congenital disease)?
Annular pancreas is a rare condition in which the second part of the duodenum is surrounded by a ring of pancreatic tissue continuous with the head of the pancreas. This portion of the pancreas can constrict the duodenum and block or impair the flow of food to the rest of the intestines.
Which germ layer forms the spleen?
Mesoderm
When does the spleen develop?
Week 5
What is the function of the spleen in the embryo?
Initially haematopoetic and develops into a lymphatic organ during weeks 15-18
Why does the spleen have notches in the adult?
Because it developed as lobes which regress
What forms from the midgut?
Second part of the duodenum Jujunum Ileum Caecum and appendix Ascending colon Proximal 2/3 of the transverse colon
How does the mid gut communicate with the yolk sac throughout its development?
Beginning of week 4: communicates with yolk sac along its length
Middle of week 4: Connection with yolk sac narrows
End week 4: connected to yolk sac vis vitelline duct
Week 5: Midgut has outgrown embryo and bulges ventrally
How does the mid gut rotate?
Rotates 90 degrees around axis of superior mesenteric artery (caudal limb on left and cranial limb on right)
The caecal bud has formed on the caudal limb
What happens to the mid gut in week 8?
Continues to grow
Small intestine forms Jejunal-ileal loops
Caecum sprouts an appendix
When does the mid gut re-enter the body cavity?
Week 10
What happens during re-entry of the mid gut to the body cavity?
Small intestine returns first During re-entry: further 180 degree rotation jejunum is displaced left and ileum right Descending colon pushed left Transverse colon pushed superiorly Caecum is the last to re-enter
What is meckel’s diverticulum?
the most common congenital abnormality of the small intestine; it is caused by an incomplete obliteration of the vitelline duct.
Complications include vitelline fistulas, cysts and ligaments
How is the definitive gut lumen formed?
Week 5/6 proliferation of mucosa Then the lumen is occluded Vacuoles develop over the next 2 weeks Recanalisation is complete by week 9. The vaccuoles help to form the villi
