Development Of The GI system Flashcards
What is the midgut?
Begins inferior to the major duodenal papilla & ends at the junction between the 2/3 & distal 1/3 of the transverse colon.
- Duodenum (inferior to the major duodenal papilla),
- Jejunum,
- Ileum,
- Cecum,
- Appendix,
- Ascending colon, and
- Right two-thirds of the transverse colon.
What are the supplies and drainages of the midgut?
Arterial supply : Superior mesenteric artery (SMA)
Venous drainage: Superior mesenteric vein
Lymphatic drainage : Superior mesenteric nodes
Describe the medgut development
Midgut elongates to form a U shaped loop which is suspended by the dorsal mesentery. It communicates with the umbilical vesicle (yolk sac) via the narrow omphaloenteric (vitelline) duct . Ventrally the loop projects into the umbilical cord [6th week→physiological umbilical hernia – because peritoneal cavity is smaller]
Describe the midgut loop function
Midgut loop has cranial and caudal limbs. The cranial limb grows rapidly and gives rise to the distal part of the duodenum, jejunum, and part of the ileum. The caudal limb gives rise to the rest of the ileum, cecum, appendix, ascending colon and proximal 2/3 of the transverse colon.
Describe the first rotation of the midgut
Within the umbilical cord midgut loop rotates 90 degrees anticlockwise around the axis of superior mesenteric artery
Rotation brings cranial limb to the right & caudal limb to the left
Describe the second midgut rotation
10Th week midgut returns to the abdominal cavity
Further 90 degrees anti-clockwise rotation occurs as the midgut
returns to the abdomen. Cranial limb returns first, occupies the
central and left part of abdomen
Describe the third midgut loop rotation
Another rotation of the viscera for 90 degrees for a total of 270 degrees.
Large intestine returns to abdomen and occupies right side.
Cecum and appendix descend to right lower quadrant of the abdomen
What is the impact of non-rotation of the midgut?
Non-rotation – caudal limb returns first →small intestine lies to the right, generally asymptomatic
What is the impact of reversed midgut rotation?
Reversed rotation – midgut loop rotates in a clockwise direction. Duodenum lies anterior to transverse colon posterior.
What is a Subhepatic Cecum and Appendix?
– Cecum gets adhered to the liver / doesn’t descend to the iliac fossa. May cause difficulty in diagnosis of appendicitis
What is a Mixed Rotation and Volvulus?
– cecum lies inferior to the pylorus and is fixed to the posterior abdominal wall by peritoneal bands.
– may cause duodenal obstruction.[due to failure of midgut loop to complete the final 900 rotation]
What is cecal diverticulum?
Cecal diverticulum – 6th week on the caudal limb of the midgut. Appendix remains narrow but increases in length. Cecum undergoes differential growth, appendix enters its medial side
What is Omphalocele?
Embryological defect: Persistence of the abdominal herniation.
Size of the hernia depends upon its contents
•In contrast to umbilical hernia it is covered by fetal membranes.
What is an umbilical hernia?
Embryological defect:
Incomplete closure of the umbilical ring
Clinical presentation:
•It appears as a soft swelling covered by skin.
•It protrudes during crying ,coughing and straining.
• Can be easily reduced through the fibrous ring at the umbilicus
•The hernia can contain omentum and small portions of the small intestines.
What is Gastroschisis?
Due to defect near the median plane of the abdominal wall.
Viscera protrudes into the amniotic cavity. Anomaly is due to incomplete closure of lateral folds during 4th week of development [1 in 10,000]