Peritoneal and GI Development Flashcards
Describe the formation of the foregut, midgut and hindgut
- crandiocaudal folding that results in the endoderm being divided into foregut, midgut and hindgut
- midgut is in free communication with the yolk sac
Describe the formation of the vitelline duct
- initially midgut is completely open into yolk sac
- as folding proceeds connection narrows and forms vitelline duct
- becomes incorporated into umbilical cord
What is Meckel’s Diverticulum?
- persistence of vitelline duct forming outpouching of ilium
- can become inflamed and harbour abnormal tissue and bacteria
What are the other ways that the vitelline duct can persist?
- vitelline cyst suspended by 2 vitelline ligaments
- vitelline fistula
Describe the formation of the oesophagus
- extension of the foregut
- at weeks 4-7 lengthens rapidly due to descent of heart and lungs
What can happen if the oesophagus does not grow properly?
a short oesophagus can result in congenital hiatus hernia
Describe the formation of the stomach
- 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
Describe the rotation of the stomach
- rotates 90 degrees clockwise around longitudinal axis (LARP - left, anterior, right, posterior)
- anteroposterior axis rotation brings pylorus upwards and fundus downwards
Describe the formation of the omental bursa
- the space posterior to the stomach
- develops with LARP rotation and small vesicles merge together and deepens bursa
Describe the formation of the greater omentum
- omentum bursa keeps growing until it overhangs
- layers of dorsal mesentery fuse together to form greater omentum
Describe the movement of the duodenum
- both a foregut and midgut structure
- as stomach rotates, duodenum moves from midline to right side of abdo cavity
Describe the initial formation of the liver and biliary system
- 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
Describe the formation of the hepatic sinusoids
hepatic cords form which intermingle with umbilical and vitelline veins
What makes up the septum transversum?
- haematopoietic cells
- Kupffer cells
- CT
Describe the formation of the pancreas
- 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
Describe the abnormalities of pancreatic development
- 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
Describe the development of the spleen
- in week 5
- develops from mesoderm
- initially is haematopoietic but develops into lymphatic organ during weeks 15-18
Describe the development of the midgut
- 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
Describe the physiological herniation of the midgut
- 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
Describe the rotation of the midgut
- 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
What is Omphalocele?
- failure of intestinal loop to return to abdomen
- high mortality rate and associated with cardiac and neural tube defects
What is Gastroschisis?
- protrusion of abdo contents through wall lateral to umbilical cord
- lower mortality rate than omphalocele as no associated defects
What are some congenital abnormalities of the gut?
- partial rotation of small intestine lateral to large intestine
- abnormal rotation where duodenum crosses over hepatic flexure
Describe the development of the hindgut
- 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
Describe some congenital abnormalities of the hindgut
Males:
- urorectal fistula
- rectoperineal fistula
Females:
- rectovaginal fistula
- anal pit
What is Hirschsprung Disease?
lack of normal development of colonic innervation - lack of peristalsis
