Gastrointestinal System Development

• The entire gastrointestinal tract originates from the endoderm.
• The esophagus develops from the tracheoesophageal septum.
• The esophagus undergoes recanalization by week 8.
• The stomach arises from the foregut region of the primitive gut tube.
• The stomach rotates approximately 90 degrees around its longitudinal axis during week 6.
• The duodenum develops from a combination of the foregut and midgut.
• The superior mesenteric artery serves as the blood supply to the midgut derivatives.
• At week 6, the midgut herniates into the umbilical cord to allow space for liver growth.
• The cecum and appendix develop from the caudal limb portion of the primary intestinal loop.
• The ascending colon is a retroperitoneal structure.
• The liver develops from the hepatic diverticulum.
• The gallbladder arises from the cystic bud.
• Bile secretion begins around week 12.
• The pancreas develops from two pancreatic buds.
• The ventral pancreatic bud gives rise to the uncinate process and part of the head of the pancreas.
• The main pancreatic duct (of Wirsung) primarily originates from both the dorsal and ventral pancreatic buds.
• Annular pancreas results from abnormal rotation of the ventral pancreatic bud.
• The hindgut terminates into the cloaca.
• The urorectal septum divides the cloaca into the urogenital sinus and anorectal canal.
• The anal canal forms from proximal endoderm and distal ectoderm.

Clinical Correlations & Anomalies

• Hirschsprung's disease is caused by failure of neural crest cell migration.
• Omphalocele results from failure of the intestines to return to the abdomen.
• Gastroschisis differs from omphalocele because the defect occurs lateral to the umbilicus.
• Meckel's diverticulum is a remnant of the vitelline duct.
• The descending colon is a derivative of the hindgut.
• The physiological herniation of the midgut occurs at week 6 of development.
• The midgut returns to the abdominal cavity at week 10.
• The cloaca is divided into the urogenital sinus and anorectal canal by the urorectal septum.
• The persistence of the vitelline duct can lead to Meckel's diverticulum.
• The dorsal mesogastrium gives rise to the greater omentum.
• The hindgut is primarily supplied by the inferior mesenteric artery.
• Failure of neural crest cell migration in the hindgut results in Hirschsprung's disease.
• The jejunum is not a derivative of the foregut.
• The body and tail of the pancreas are derived from the dorsal pancreatic bud.
• The pectinate line is an embryological landmark that separates the endoderm from the ectoderm in the anal canal.
• The liver arises from the foregut.
• The esophagus and trachea are separated by the tracheoesophageal folds.
• A newborn presents with bilious vomiting and a double-bubble sign on X-ray. The most likely embryological defect is duodenal atresia.
• The gallbladder and cystic duct originate from the cystic bud.
• A persistent cloacal membrane would result in anal agenesis.
• The anal canal above the pectinate line drains into the portal venous system.
• Incomplete rotation of the midgut results in malrotation with volvulus.
• Failure of the duodenum to recanalize can lead to duodenal atresia.
• A patient presents with a remnant of the vitelline duct that secretes gastric acid, leading to ulceration, this condition is known as Meckel's diverticulum.
• The umbilical vein gives rise to the round ligament of the liver.
• The sigmoid colon is intraperitoneal.
• The dorsal mesogastrium contributes to the formation of the greater omentum.
• The ventral mesogastrium gives rise to the lesser omentum.
• The vitelline duct normally obliterates by week 7.
• Pyloric stenosis is caused by hypertrophy of the circular layer of the muscularis externa.

Midgut, Hindgut, and Related Anomalies

• The primary function of the yolk sac in early embryonic development is to serve as a site for early blood cell formation.
• Meckel's diverticulum is a remnant of the vitelline duct.
• The inferior mesenteric artery supplies the sigmoid colon.
• The hindgut gives rise to the sigmoid colon.
• The anorectal canal is derived from the cloaca and ectoderm.
• The junction between the midgut and hindgut is marked by the splenic flexure.
• The most common congenital anomaly of the GI tract is Meckel's diverticulum.
• The rotation of the midgut occurs around the superior mesenteric artery.
• The midgut rotates a total of 270 degrees counterclockwise.
• Malrotation of the midgut can result in volvulus.
• The urorectal septum separates the cloaca into the urogenital sinus and anorectal canal.
• The anal canal above the pectinate line is derived from endoderm.
• The anal canal below the pectinate line is derived from ectoderm.
• The venous drainage above the pectinate line is primarily through the portal venous system.
• The venous drainage below the pectinate line is primarily through the caval venous system.
• The innervation above the pectinate line is primarily autonomic (involuntary).
• The innervation below the pectinate line is primarily somatic (voluntary).
• A rectourethral fistula is caused by incomplete division of the cloaca.
• The most common type of tracheoesophageal fistula is esophageal atresia with a distal fistula.
• Failure of the anal membrane to perforate leads to imperforate anus.
• Affects the esophagus is not a feature of Hirschsprung's disease.
• Omphalocele and gastroschisis both involve failure of closure of the anterior abdominal wall.
• Failure of the duodenum to recanalize is associated with duodenal atresia.
• Esophageal atresia is associated with polyhydramnios during pregnancy.
• The liver grows into the septum transversum.

Advanced Concepts & Clinical Correlations

• The falciform ligament is a derivative of the ventral mesogastrium.
• The ligamentum teres hepatis is a remnant of the umbilical vein.
• The pancreas is formed by the fusion of the dorsal and ventral pancreatic buds.
• The ventral pancreatic bud gives rise to the head and uncinate process.
• The ventral mesogastrium contributes to the lesser omentum.
• A newborn diagnosed with annular pancreas results from abnormal migration of the ventral pancreatic bud.
• The most common site of a Meckel's diverticulum is the ileum.
• Failure of neural crest cell migration to the distal colon results in Hirschsprung's disease.
• The mesoderm of the dorsal mesogastrium contributes to the development of the spleen.
• During the 5th week of development, the liver and biliary system develop from the hepatic diverticulum.
• Esophageal atresia is associated with polyhydramnios due to the fetus's inability to swallow amniotic fluid.
• The common bile duct is derived from the hepatic diverticulum.
• Midgut volvulus is a complication of abnormal midgut rotation.
• The spleen develops within the dorsal mesogastrium but receives its blood supply from the celiac artery.
• Omphalocele occurs due to failure of the midgut to return to the abdominal cavity.
• The vitelline veins contribute to the formation of the hepatic portal vein.
• The gallbladder originates from the cystic diverticulum.
• The cloaca is the common embryonic structure for the urinary and digestive tracts.
• Hypertrophy of the pyloric muscle leading to non-bilious vomiting is due to pyloric stenosis.
• The embryonic midgut communicates with the yolk sac via the vitelline duct.
• The greater omentum is formed from the dorsal mesogastrium.
• The caudal portion of the hindgut gives rise to the descending colon and rectum.
• The rotation of the stomach creates greater and lesser sacs.
• In duodenal atresia, a double-bubble sign is commonly seen radiologically.
• The lesser omentum is derived from the ventral mesentery.