Embryology: Development of the peritoneum and foregut

Question 1

Outline the embryonic folding in the 4th week

Answer 1

Lateral folding - creates a ventral wall and forms a tubular primitive gut
Craniocaudally - creates cranial and caudal pockets from the yolk sac endoderm which is the beginning of primitive gut development

Question 2

What is the primitive gut tube?

Answer 2

The primitive gut tubes pinches off from the yolk sac in the 3rd week
It runs from the future mouth to the future anus with an opening at the umbilicus

Question 3

What is the germ layer derivative of the primitive gut tube?

What will each lining become?

Answer 3

Internal lining derived from endoderm and will become the future epithelial linings
External lining derived from splanchnic mesoderm and will become future musculature and visceral perioteum

Question 4

What is the arterial supply of the foregut, midgut and hindgut?

Answer 4

Foregut - celiac trunk
Midgut - superior mesenteric artery
Hindgut - inferior mesenteric artery

Question 5

What is the intraembryonic coelom?

Answer 5

Begins as one large cavity the entire length of the embryo then is subdivided by the future diaphragm into abdominal and thoracic cavities.

Question 6

What is mesentery formed out of?

Answer 6

The primitive gut is suspended in the intraembryonic coelum by splanchnic mesoderm
The mesentery is formed by a condensation of this splanchnic mesoderm

Question 7

What do the dorsal and ventral mesenteries suspend?

Answer 7

Dorsal mesentery suspends the entire gut tube from the dorsal body wall
Ventral mesentery only suspends the foregut creating a free edge

Question 8

In the foregut how are the greater and lesser peritoneal sacs formed?

Answer 8

There are both ventral and dorsal mesenteries so these divide the cavity into left and right sac

• the left sac contributes to the greater sac
• the right sac becomes the lesser sac

Question 9

What are the greater and lesser omenta?

Answer 9

Omenta are specialised regions of peritoneum

• the greater omentum is formed from dorsal mesentery
• the lesser omentum is formed from ventral mesentery

Question 10

What is formed when there is rotation of the primitive stomach?

Answer 10

• The cardia and pylorus move horizontally which pushes the greater curvature inferiorly
• Puts he vagus nerve anterior and posterior of the stomach
• Creates the greater omentum
• Puts the lesser sac behind the stomach

Question 11

What is the difference between retroperitoneal and secondarily retroperitoneal structures?

Answer 11

Retroperitoneal structures were never in the peritoneal cavity and never had a mesentery
Secondarily retroperitoeal structures began development in the peritoneum and had a mesentery which then regresses through fusion to the posterior abdo wall
(eg duodenum except cap, pancreas)

Question 12

What are some consequences of abnormal positioning of the tracheoesophageal septum?

Answer 12

Can get a range of oesophageal abnormalities (1 in 3000 live births)

• blind end oesophagus and a tracheoesophageal fistula
• 2 parts of blind ended oesophagus
• 2 tracheoesophageal fistulas