Embryology

Question 1

Which germ layer gives rise to the epithilium of the GI tract and associated ducts and glands?

Answer 1

Endoderm

Question 2

Which germ layer gives rise to the lamina propria, muscularis mucosae, muscularis externa, the connective tissue of submucosa and adventicia?

Answer 2

Visceral mesoderm

Question 3

What is formed from the ventral mesentaries?

Answer 3

Lesser omentum and the falciform ligament

Question 4

What is formed form the dorsal mesentries?

Answer 4

Doral mesogastrium, dorsal mesoduodenum, Dorsal mesocolon

Question 5

What is the vitelline duct?

Answer 5

long narrow tube that joins the yolk sac to the midgut lumen

Question 6

What does the cloaca form?

Answer 6

Some of the hind gut and urogenital system

Question 7

What causes the mesenteries to come to there final positions?

Answer 7

Rotation of different parts of the gut

Question 8

When is the oesophagus distinguishable?

When does the circular and longitudinal muscle develop?

Answer 8

Distinguishable by the end of week 4
Circular muscle develops week 5
Longitudinal muscle develops week 8

Question 9

How does the stomach develop?

Answer 9

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.

Question 10

What creates the lesser sac causing the dorsal mesentery to bulge?

Answer 10

Growth and rotation of the stomach

Question 11

What forms the greater omentum?

Answer 11

Continued growth of the dorsal mesentary

Question 12

What forms the horizontal (1) and descending (2) parts of the duodenum?

Answer 12

Caudal portion of the foregut

Question 13

What forms the horizontal (3) and ascending (4) parts to the duodenum?

Answer 13

Cranial part of the mid gut

Question 14

Why is the duodenal loop directed to the right?

Answer 14

Rotation of the stomach

Question 15

How does the liver form?

Answer 15

Liver bud grows into the mesoderm of Septum Transversum.

Question 16

What is contained within the sepum transversum?

Answer 16

Haematopioetic cells
Kupffer cells
Connective tissue

Question 17

What germ layer forms the liver cells and the lining of the billary tree?

Answer 17

Endoderm

Question 18

How does the pancreas form?

Answer 18

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

Question 19

The pancreas develops intraperitoneal and then upon rotation becomes retroperitoneal. T or F?

Answer 19

True

Question 20

What is annular pancreas (congenital disease)?

Answer 20

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.

Question 21

Which germ layer forms the spleen?

Answer 21

Mesoderm

Question 22

When does the spleen develop?

Answer 22

Week 5

Question 23

What is the function of the spleen in the embryo?

Answer 23

Initially haematopoetic and develops into a lymphatic organ during weeks 15-18

Question 24

Why does the spleen have notches in the adult?

Answer 24

Because it developed as lobes which regress

Question 25

What forms from the midgut?

Answer 25

``` Second part of the duodenum Jujunum Ileum Caecum and appendix Ascending colon Proximal 2/3 of the transverse colon ```

Question 26

How does the mid gut communicate with the yolk sac throughout its development?

Answer 26

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

Question 27

How does the mid gut rotate?

Answer 27

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

Question 28

What happens to the mid gut in week 8?

Answer 28

Continues to grow Small intestine forms Jejunal-ileal loops Caecum sprouts an appendix

Question 29

When does the mid gut re-enter the body cavity?

Answer 29

Week 10

Question 30

What happens during re-entry of the mid gut to the body cavity?

Answer 30

``` 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 ```

Question 31

What is meckel's diverticulum?

Answer 31

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

Question 32

How is the definitive gut lumen formed?

Answer 32

``` 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 ```