Peritoneal and GI Development Flashcards
Describe the formation of the fore, mid and hindgut
Craniocaudal folding results in the endoderm being subdivided into foregut, midgut and hindgut with the midgut in free communication with the yolk sac.
Describe the formation of the vitelline duct
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
What is Meckel’s Diverticulum?
It is a persistence of the vitelline duct forming an outpouching of the ilium. It may become inflamed and harbour abnormal tissue and bacteria
Name other ways that the vitelline duct can persist?
- Vitelline cyst suspended by two vitelline ligaments,
- Vitelline fistula.
Describe the formation of the oesophagus
- Extension of the foregut and at weeks 4-7 it lengthens rapidly due to descent of the heart and lungs
Failure of the oesophagus to grow in proportion can result in what?
A short oesophagus which can result in a congenital hiatus hernia
Describe the formation of the stomach
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
Explain the rotation of the stomach
The stomach rotates 90 degrees clockwise around the longitudinal axis (LARP - left anterior, right posterior). Anteroposterior axis rotation brings pylorus upwards and fundus downwards.
Describe the formation of the Omental Bursa
The omental bursa is the space posterior to the stomach. It develops with LARP rotation and small vesicles merge together and deepens the bursa.
Describe the formation of the greater omentum
The omentum bursa continues to grow until it starts to overhang. The layers of the dorsal mesentery fuse together to form the greater omentum.
Describe the formation of the duodenum
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.
Describe the initial formation of the liver and billary system
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.
Describe the formation of hepatic sinusoids
Hepatic cords form which intermingle with the umbilical (oxygen rich blood) and vitelline veins (nutrient rich)
What is the septum transversum made up of?
Hematopoietic cells, Kupffer cells and CT
Describe the formation of the pancreas
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.
Describe the abnormalities of pancreatic development
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.
Describe the development of the spleen
IN week 5 it develops from mesoderm. Initially it is haematopoietic but then develops into a lymphatic organ during weeks 15-18
Explain the development of the midgut
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.
Explain the physiological herniation of the midgut
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.
Explain rotation of the midgut
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.
What is Omphalocele and Gastroschisis?
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.
What are some congenital abnormalities of the midgut
Partial rotation (small intestine lateral to large) and abnormal rotation where duodenum crosses over hepatic flexure
Explain the development of the hindgut
- 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.
Describe some congenital abnormalities of the hindgut
Males - Urorectal fistula or rectoperineal fistula.
Females - Rectovaginal fistula or anal pit.
What is Hirschsprung Disease?
Lack of normal development of the colonic innervation - lack of peristalsis
