Embryology

Question 1

Which germ layers is the GI tract formed from?

Answer 1

Endoderm = Lining of gut tube

Visceral Mesoderm = Muscle layers etc.

Question 2

What are the dorsal mesenteries, and which structure are they associated with?

Answer 2

Dorsal mesogastrium = Stomach

Dorsal mesoduodenum = Duodenum. Proximal part retains its mesentery, rest becomes retroperitoneal

Mesentery proper

Dorsal mesocolon = Transverse and sigmoid retain their mesenteries, rest becomes retroperitoneal during development

Question 3

What are the ventral mesenteries?

Answer 3

Lesser omentum

Falciform ligament

Question 4

What does the dorsal mesogastrium give in the adult?

Answer 4

Greater omentum

Question 5

At which point does the oesophagus become distinguishable?

Answer 5

End of week 4

Question 6

At which points do the circular and longitudinal muscles of the oesophagus develop?

Answer 6

Circular = Week 5 
Longitudinal = Week 8

Question 7

How does the stomach develop?

Answer 7

Dilation of caudal part of the foregut
Dorsal border grows paisley, forming greater and lesser curvatures
Causes bending of the tube
Stomach rotates 90 degrees about both longitudinal and AP axis
Formation of vacuoles helps accommodate rotation of the stomach

Question 8

How does stomach growth affect omenta?

Answer 8

Growth and rotation of the stomach creates lesser sac and causes dorsal mesentery to bulge
Continued growth of dorsal mesentery forms greater momentum
Lesser omentum and falciform ligament form from ventral mesentery

Question 9

From which parts of the gut tube to the individual parts of the duodenum form?

Answer 9

Parts 1 and 2 of duodenum = Caudal portion of foregut

Parts 3 and 4 of duodenum =
Cranial portion of midgut

Question 10

How does stomach growth affect the duodenum?

Answer 10

Duodenal loo is directed to the right due to rotation of the stomach

Question 11

From which layers does the liver develop?

Answer 11

Endoderm (from duodenum) = Liver cells and lining of biliary tree

Septum transversum = Hematopioetic cells, Kupffer cells, connective tissue

Question 12

Into where does the liver bud grow?

Answer 12

Mesoderm of Septum Transversum

Question 13

Why is the growth of the liver disproportionally rapid at the early stages of development?

Answer 13

Allows for production of red blood cells

Question 14

Which two components make up the embryonic pancreas?

Answer 14

Ventral and dorsal pancreatic buds

Question 15

How does the pancreas develop?

Answer 15

Th ventral pancreatic bud migrates around the duodenum to get to the final adult position alongside the dorsal pancreatic bud
The two buds will fuse over time and form one communication with the duodenum

Question 16

What is an annular pancreas?

Answer 16

Solid glandular tissue of the ventral pancreatic duct surrounds the duodenum
Can cause construction and narrowing/stenosis of the duodenum

Question 17

From where does the spleen originate?

Answer 17

Mesoderm derivative (not form the gut tube)

Question 18

When does the spleen start to develop?

Answer 18

5th week

Question 19

What change in function does the spleen undergo sprung development?

Answer 19

Initially haematopoetic

Develops into lymphatic organ during weeks 15-18

Question 20

What is the appearance of the spleen during development?

Answer 20

Lobular appearance

Lobes normally regress before birth

Question 21

Which organs are associated with the midgut?

Answer 21

Second half of the duodenum 
Jejunum 
Ileum 
Caecum and appendix 
Ascending colon 
Proximal 2/3 transverse colon

Question 22

How does the midgut’s communication with the yolk sac develop?

Answer 22

Start of week 4 = Communicates with yolk sac along its length
This connection narrows until the vitelline duct has formed

Question 23

What happens to the midgut around week 5 of development?

Answer 23

The midgut has outgrown the embryo and bulges ventrally (physiological hernia through the umbilicus)

Question 24

How does the midgut rotate during development?

Answer 24

Rotates 90 degrees around axis of SMA
Caudal limb is on the left, cranial on the right
Caecal bud forms on causal limb

Question 25

What growth happens to the midgut whilst outside of the abdominal cavity?

Answer 25

Small insetting starts to fold o itself
Jejunal-ileal loops form
Caecum sprouts an appendix

Question 26

When does the midgut return to the body cavity?

Answer 26

Week 10

Question 27

What happens during the midguts return to the body cavity?

Answer 27

Small intestine returns first 
Further 180 rotation 
Jejunum displaced left and ileum right 
Descending colon pushed left 
Transverse colon pushed superiorly 
Caecum is last to re-enter

Question 28

What is Meckel’s Diverticulum?

Answer 28

Persistent attachment of the small intestine to the umbilicus

Question 29

What are the defects of the small intestine?

Answer 29

Vitelline Fistula
Vitelline Cyst
Vitelline Ligament
Meckel’s Diverticulum

Question 30

What is the cloaca?

Answer 30

An expansion of the endoderm which gives rise to the hindgut

Question 31

What is the purpose of the urorectal septum?

Answer 31

Divides the cloaca into the part which ill give rise to the handgun, and the part which will give rise to the urogenital system

Question 32

How does the definitive gut lumen develop?

Answer 32

At week 5/6, there is proliferation of mucosa and thehollow gut tube becomes occluded
Vacuoles develop of the next 2 weeks
Recanalisation is complete by week 9