Peritoneal and GI Development

Question 1

Describe the formation of the foregut, midgut and hindgut

Answer 1

• crandiocaudal folding that results in the endoderm being divided into foregut, midgut and hindgut
• midgut is in free communication with the yolk sac

Question 2

Describe the formation of the vitelline duct

Answer 2

• initially midgut is completely open into yolk sac
• as folding proceeds connection narrows and forms vitelline duct
• becomes incorporated into umbilical cord

Question 3

What is Meckel’s Diverticulum?

Answer 3

• persistence of vitelline duct forming outpouching of ilium

- can become inflamed and harbour abnormal tissue and bacteria

Question 4

What are the other ways that the vitelline duct can persist?

Answer 4

• vitelline cyst suspended by 2 vitelline ligaments

- vitelline fistula

Question 5

Describe the formation of the oesophagus

Answer 5

• extension of the foregut

- at weeks 4-7 lengthens rapidly due to descent of heart and lungs

Question 6

What can happen if the oesophagus does not grow properly?

Answer 6

a short oesophagus can result in congenital hiatus hernia

Question 7

Describe the formation of the stomach

Answer 7

• at week 4 starts as a fusiform dilation
• dorsal wall then grows rapidly to form greater curvature
• ventral growth is slower to form lesser curvature

Question 8

Describe the rotation of the stomach

Answer 8

• rotates 90 degrees clockwise around 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 space posterior to the stomach

- develops with LARP rotation and small vesicles merge together and deepens bursa

Question 10

Describe the formation of the greater omentum

Answer 10

• omentum bursa keeps growing until it overhangs

- layers of dorsal mesentery fuse together to form greater omentum

Question 11

Describe the movement of the duodenum

Answer 11

• both a foregut and midgut structure

- as stomach rotates, duodenum moves from midline to right side of abdo cavity

Question 12

Describe the initial formation of the liver and biliary system

Answer 12

• ventral outgrowth (hepatic diverticulum) of foregut at end of week 3 into ventral mesentery
• penetrates the septum transversum
• cranial portion becomes liver
• caudal portion becomes bile duct

Question 13

Describe the formation of the hepatic sinusoids

Answer 13

hepatic cords form which intermingle with umbilical and vitelline veins

Question 14

What makes up the septum transversum?

Answer 14

• haematopoietic cells
• Kupffer cells
• CT

Question 15

Describe the formation of the pancreas

Answer 15

• inferior to hepatic diverticulum, ventral pancreatic bud forms
• posterior to hepatic diverticulum, dorsal pancreatic bud forms (grows bigger)
• due to LARP rotation ventral bud is moved more posteriorly
• dorsal pancreatic duct joins ventral duct to form major pancreatic duct

Question 16

Describe the abnormalities of pancreatic development

Answer 16

• ventral pancreatic bud can be bilobed so when rotation occurs one of the ventral buds will be rotated the other way making an annular pancreas
• can stenos the duodenum

Question 17

Describe the development of the spleen

Answer 17

• in week 5
• develops from mesoderm
• initially is haematopoietic but develops into lymphatic organ during weeks 15-18

Question 18

Describe the development of the midgut

Answer 18

• in week 5 midgut rapidly expands forming primary intestinal loop
• cranial limb will form distal duodenum, jejunum and upper limb
• caudal limb forms lower ileum, caecum, ascending colon and proximal 2/3rds transverse colon

Question 19

Describe the physiological herniation of the midgut

Answer 19

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

Question 20

Describe the rotation of the midgut

Answer 20

• as lengthening proceeds, midgut rotates 90 degrees clockwise
• small and large intestine growth continues with small to form coils
• in week 10, intestines will retract back into abdomen and rotate 180 degrees clockwise
• caecal bud descends from right lobe of liver to form right iliac fossa

Question 21

What is Omphalocele?

Answer 21

• failure of intestinal loop to return to abdomen

- high mortality rate and associated with cardiac and neural tube defects

Question 22

What is Gastroschisis?

Answer 22

• protrusion of abdo contents through wall lateral to umbilical cord
• lower mortality rate than omphalocele as no associated defects

Question 23

What are some congenital abnormalities of the gut?

Answer 23

• partial rotation of small intestine lateral to large intestine
• abnormal rotation where duodenum crosses over hepatic flexure

Question 24

Describe the development of the hindgut

Answer 24

• terminal end is an endodermal lined pouch called cloaca
• in contact with surface ectoderm of proctodeum to form cloacal membrane
• urorectal septum partitions cloaca into upper anal canal and urogenital sinus

Question 25

Describe some congenital abnormalities of the hindgut

Answer 25

Males:

• urorectal fistula
• rectoperineal fistula

Females:

• rectovaginal fistula
• anal pit

Question 26

What is Hirschsprung Disease?

Answer 26

lack of normal development of colonic innervation - lack of peristalsis