GI Embryology Flashcards
As usual, erring on the side of too much detail... I don't love Kessler's embryo lectures.
What structure becomes the umbilicus? What does it do?
Vitelline duct - maintains continuity with yolk sac.
What structure seals the future site of the oral cavity?
The buccopharyngeal membrane
What invaginates and seals to capure the gut lumen? What does the part that fuses become?
Yolk sac roof folds down…. captures lumen of gut tube.
Fuses at the ventral midline.
What structure seals the future site of the rectum?
The cloacal membrane
What happens to the gut tube before you get the “definitive hollow gut”? 3 things that can go wrong here?
It starts hollow, is occluded by endodermal proliferation, then recanalized. 3 problems: Duplication (creating a flap thing). Stenosis. Atresia (complete blockage of tube).
What are the major arteries that supply thoracic foregut, abdominal foregut, midgut, and hindgut?
Thoracic foregut: aortic arches.
Abdominal foregut: Celiac trunk
Midgut: Superior mesenteric artery
Hindgut: Inferior mesenteric artery
Review: Where does midgut start?
Right at the ampulla of Vater.
Review: Where does the hindgut start?
The distal 1/3 of the transverse colon.
Where do the lungs come from? (among the things mentioned in this lecture)
Thoracic foregut.
What is esophageal atresis and stenosis? What causes it?
Blockage or narrowing of esophagus.
Usu. due to failure of recanalization.
What is tracheoesophageal fistula?
Caudal displacement of septum between trachea and esophagus. (there’s a better description of this in the esophageal and gastric pathology lecture)
What is congenital hiatal hernia? What causes it?
Part of stomach is herniated into thoracic cavity.
Caused here by a failure of the esophagus to elongate.
So the gut has dorsal and ventral mesenteries. Which extends all the way? Which is only part way, and how part does it go?
Dorsal mesentery is on whole length of gut.
Ventral mesentery is just on the foregut.
Which side of the stomach becomes the greater curvature? How does this rotate?
Dorsal becomes greater curvature (and dorsal mesentery becomes greater omentum).
Rotates 90 degrees such that greater curvature faces left.
What change in the mesentery helps drive stomach rotation?
Differential thinning of the dorsal mesentery.
What is duodenal atresia and stenosis?
Just like in esophagus, failure of recanalization causes blockage / narrowing.
What does duodenal atresia look like on ultrasound? Why?
“Double-bubble” - because stomach and proximal duodenum are dilated with stuff that can’t get through.
What spaces does the rotation of the stomach define? What connects these two spaces?
This defines the lesser sac dorsal to the stomach (and… the rest of the peritoneum).
They’re connected by the epiploic foramen.
What develops on the ventral surface of the proximal duodenum (day 22)?
The hepatic plate/diverticulum
What connects the liver to the stomach?
Lesser omentum (ventral mesentery)
What connects the liver to the body wall?
The falciform ligament.
So the cystic diverticulum…
Grows, if not off of, pretty near the hepatic diverticulum… which makes sense.
2 anomalies of liver and cystic ducts?
Gall bladder duplication - usually asymptomatic.
Extrahepatic biliary atresia - failure to canalize.
How does the pancreas form?
As two buds, dorsal and ventral, which fuse together.
Which duct becomes the main pancreatic connection to the duodenum?
The ventral duct.
What is annular pancreas? Why is this a problem?
Ventral and dorsal buds fuse such that they wrap around the duodenum, blocking it off or causing stenosis.
Where does the pancreas end up?
Dorsal mesentery gets fixed onto dorsal body wall… most of it becomes “secondarily retroperitoneal.”
Which gut structures are secondarily retroperitoneal?
Duodenum, pancreas, colon.
Which gut structures are intraperitoneal?
Stomch, gallbladder, transverse colon.
Which gut structures are retroperitoneal?
Thoracic esophagus, rectum.
Where does the primary intestinal loop (the part that becomes ileum and large bowel) go? How does it rotate?
Herniates out into umbilical region and rotates.
Cranial part goes 90 degrees right.
Caudal part goes 90 degrees left.
What happens when the primary intestinal loops retracts?
It rotates 180 degrees, bringing it to the final, adult position.
What’s the difference between a congenital omphocele and an umbilical hernia?
In congenital omphocele, the midgut never retracted out of the umbilical cord.
In umbilical hernia, the midgut retracted, but the umbilicus didn’t fully close, and stuff re-herniated.
What is gastroschisis?
Midgut structures extrude through the ventral body wall. (doesn’t include umbilicus)
What is Ileal (Meckel’s) Diverticulum?
Remnant of the yolk stalk persists as outpouching. Can contain gastric or pancreatic tissue, causes appendicitis-like symptoms.
What can happen if proper rotation doesn’t occur?
Things can twist (volvulus) and occlude eachother.
What separates the rectum from the urogenital sinus early on?
The urorectal septum - forms in the cloaca.
What’s the visible junction between the ectoderm and endoderm in the anus?
The pectinate line
Review: What causes congenital megacolon (Hirschsprung’s Disease)?
Dilatation of colon - no peristalsis because there are no ganglia. (Neural crest cells failed to migrate)
What’s membranous atresia?
Failure of anal perforation… easy to fix with surgery.
In aganglionic megacolon, which part is dilated?
The part of the colon proximal to the aganglionic area is dilated.
