Peritoneal and GI Development

Question 1

Describe the formation of the fore, mid and hindgut

Answer 1

Craniocaudal folding results in the endoderm being subdivided into foregut, midgut and hindgut with the midgut in free communication with the yolk sac.

Question 2

Describe the formation of the vitelline duct

Answer 2

Initially the midgut is completely open into the yolk sac but as folding continues the connection between them narrows and froms the vitelline duct. It becomes incorporated into the umbilical cord

Question 3

What is Meckel’s Diverticulum?

Answer 3

It is a persistence of the vitelline duct forming an outpouching of the ilium. It may become inflamed and harbour abnormal tissue and bacteria

Question 4

Name other ways that the vitelline duct can persist?

Answer 4

• Vitelline cyst suspended by two vitelline ligaments,

- Vitelline fistula.

Question 5

Describe the formation of the oesophagus

Answer 5

• Extension of the foregut and at weeks 4-7 it lengthens rapidly due to descent of the heart and lungs

Question 6

Failure of the oesophagus to grow in proportion can result in what?

Answer 6

A short oesophagus which can result in a congenital hiatus hernia

Question 7

Describe the formation of the stomach

Answer 7

At week 4 the stomach starts as a fusiform dilation. The dorsal wall undergoes rapid growth to form the curvature where as the ventral growth is slower, resulting in the lesser curvature

Question 8

Explain the rotation of the stomach

Answer 8

The stomach rotates 90 degrees clockwise around the longitudinal axis (LARP - left anterior, right posterior). Anteroposterior axis rotation brings pylorus upwards and fundus downwards.

Question 9

Describe the formation of the Omental Bursa

Answer 9

The omental bursa is the space posterior to the stomach. It develops with LARP rotation and small vesicles merge together and deepens the bursa.

Question 10

Describe the formation of the greater omentum

Answer 10

The omentum bursa continues to grow until it starts to overhang. The layers of the dorsal mesentery fuse together to form the greater omentum.

Question 11

Describe the formation of the duodenum

Answer 11

It is both a foregut and midgut structure. As the stomach rotates the duodenum moves from the midline to the right-side of the abdominal cavity.

Question 12

Describe the initial formation of the liver and billary system

Answer 12

A ventral outgrowth (hepatic diverticulum) of the foregut at the end of week 3 into the ventral mesentery. It then penetrates the septum transversum. The cranial portion will become the liver and caudal portion will become the bile duct.

Question 13

Describe the formation of hepatic sinusoids

Answer 13

Hepatic cords form which intermingle with the umbilical (oxygen rich blood) and vitelline veins (nutrient rich)

Question 14

What is the septum transversum made up of?

Answer 14

Hematopoietic cells, Kupffer cells and CT

Question 15

Describe the formation of the pancreas

Answer 15

Inferior to the hepatic diverticulum, the ventral pancreatic bud forms. Posterior to the hepatic diverticulum the dorsal pancreatic bud forms, the dorsal bud grows much bigger. Due to LARP rotation the ventral bud is moved posteriorly. The dorsal pancreatic duct joins the ventral duct to form the major pancreatic duct.

Question 16

Describe the abnormalities of pancreatic development

Answer 16

The ventral pancreatic bud can be bilobed and so when rotation occurs one of the ventral buds rotated the other way, making annular pancreas. This can stenos the duodenum.

Question 17

Describe the development of the spleen

Answer 17

IN week 5 it develops from mesoderm. Initially it is haematopoietic but then develops into a lymphatic organ during weeks 15-18

Question 18

Explain the development of the midgut

Answer 18

In week 5 the mid gut rapidly expands forming the primary intestinal loop. The cranial limb will form distal duodenum, jejunum and upper limb. Caudal limb will form lower ileum, cecum, ascending colon and proximal 2/3rds of transverse colon.

Question 19

Explain the physiological herniation of the midgut

Answer 19

In week 6, the rapid growth and expansion of the liver causes physiological herniation of the midgut. The intestinal loops move through umbilical cord to lie outside the developing embryo. It will later be pulled back in.

Question 20

Explain rotation of the midgut

Answer 20

As the lengthening continues, the midgut rotates 90 degrees clockwise. The small and large intestine growth continues with the small forming coils. During week 10, the intestines retract back into abdomen with a further 180 degree clockwise turn (270 total). The cecal bud descends from right lobe of liver to form right iliac fossa.

Question 21

What is Omphalocele and Gastroschisis?

Answer 21

Omphalocele - Failure of intestinal loop to return into abdomen. It has a high mortality rate and is often associated with cardiac and neural tube defects.
Gastroschisis - Protrusion of abdo contents through the wall lateral to umbilical cord. Lower mortality rate as no associated defects.

Question 22

What are some congenital abnormalities of the midgut

Answer 22

Partial rotation (small intestine lateral to large) and abnormal rotation where duodenum crosses over hepatic flexure

Question 23

Explain the development of the hindgut

Answer 23

• Terminal end of hindgut is an endodermal-lined pouch called cloaca. It is in contact with surface ectoderm of proctodeum to form cloacal membrane. The urorectal septum partitions the cloaca into upper anal canal and urogenital sinus.

Question 24

Describe some congenital abnormalities of the hindgut

Answer 24

Males - Urorectal fistula or rectoperineal fistula.

Females - Rectovaginal fistula or anal pit.

Question 25

What is Hirschsprung Disease?

Answer 25

Lack of normal development of the colonic innervation - lack of peristalsis