Flashcards in GI Embryology Deck (50)
At 20 dpf, what is the structure of the embryo?
A flat, trilaminar embryonic disc.
By 26 dpf, what structure lies at the termination of the cranial end of the gut tube?
The buccopharyngeal membrane (or stomodeum).
By 26 dpf, what structure lies at the termination of the caudal end of the gut tube?
The cloacal membrane (or proctodeum).
By 26 dpf, the narrowing of the yolk sac yields what structure? What later structure is this incorporated into?
The vitelline duct.
The umbilical cord.
Describes the steps that the endodermal epithelium of the gut tube undergoes before arriving at the definitive mucosal epithelium in week 9.
(1) Proliferation, to the point where the tube is completely occluded.
(2) Recanalization, i.e. degeneration of the central tissue through vacuole formation.
What structures comprise the foregut?
Pharynx, thoracic esophagus, abdominal esophagus, stomach, superior duodenum.
What structures comprise the midgut?
Inferior duodenum, jejunum, ileum, cecum, appendix, ascending colon, transverse colon (first 2/3).
What structures comprise the hindgut?
Transverse colon (latter 1/3), descending colon, sigmoid colon, rectum.
What vessel supplies the abdominal foregut?
The celiac artery.
What vessel supplies the midgut?
The superior mesenteric artery.
What vessel supplies the hindgut?
The inferior mesenteric artery.
What vessel supplies the thoracic foregut?
By 28 dpf, what cavity forms from the completion of embryonic folding? What later cavity will it become?
The intraembryonic coelom.
The peritoneal cavity.
Describe the steps involved in the formation of the rudimentary lungs.
(1) The respiratory diverticulum appears as a ventral outpouching of the thoracic esophagus.
(2) The lung bud grows out into the surrounding mesenchyme, bifurcating into the L and R bronchial buds.
What is embryonic folding?
The cranial, lateral, and caudal invagination of the yolk sac roof.
What is esophageal atresia?
A complete blockage of the esophagus due to a failure of recanalization.
What is esophageal stenosis?
A narrowing of the esophagus due to a failure of canalization.
What is a tracheoesophageal fistula?
A caudal displacement of the septum between the trachea and esophagus that results in an incomplete separation of the respiratory and esophageal tubes.
What is a congenital hiatal hernia?
A displacement of the stomach into the thoracic cavity due to a failure of the esophagus to elongate.
Describe the steps involved in the formation of the rudimentary stomach.
(1) The dorsal wall of the relevant part of the gut tube grows more rapidly than the ventral wall, forming the greater and lesser curvatures.
(2) Differential thinning of the dorsal mesentery results in a 90 degree rotation of the greater curvature of the stomach to the left.
What is duodenal atresia?
A complete blockage of the duodenum due to a failure of recanalization.
What is duodenal stenosis?
A narrowing of the duodenum due to a failure of recanalization.
How does duodenal atresia appear on ultrasound?
As a "double bubble," as the stomach and proximal duodenum are dilated and fluid-filled.
From what is the greater omentum derived?
Dorsal mesentery of the stomach.
From what is the lesser omentum derived?
Ventral mesentery of the stomach.
What landmark connects the two compartments of the peritoneal cavity?
The epiploic foramen.
Describe the formation of the rudimentary liver.
(1) The hepatic plate forms on the ventral duodenum.
(2) The plate proliferates into the ventral mesentery, forming the hepatic diverticulum.
(3) The diverticulum gives rise to the hepatic cords, hepatic duct and the bile canaliculi.
What structure connects the liver to the ventral body wall?
The falciform ligament.
Describe the formation of the rudimentary gall bladder.
(1) The cystic diverticulum forms on the ventral duodenum, caudal to the hepatic diverticulum. The gall bladder and cystic duct form from this structure.
(2) Cells at the juncture of the hepatic and cystic ducts proliferate and form the bile duct.
What GI organ is most frequently duplicated?
The gall bladder.
What is extrahepatic biliary atresia?
A complete obstruction of the bile duct due to a failure of recanalization.
Describe the formation of the rudimentary pancreas.
(1) The dorsal pancreatic bud forms on the duodenum and grows into the dorsal mesentery. Similarly, the ventral pancreatic bud forms on the duodenum, caudal to the hepatic and cystic diverticula, and grows into the ventral mesentery.
(2) The ventral bud migrates around the duodenum and fuses with the dorsal bud.
(3) The dorsal pancreatic duct degenerates.
From what does the main pancreatic duct derive?
The duct of the ventral pancreatic bud.
What is an anular pancreas?
When the two buds of a bifid pancreatic bud rotate in opposite directions around the duodenum and fuse with the dorsal bud. Duodenal stenosis or atresia results.
J: When structures originally suspended from mesenteries become attached to the body wall.
What is secondarily retroperitoneal?
J: When structures are suspended from mesenteries.
What is intraperitoneal?
J: When structures are attached to the body wall outside of the peritoneal cavity.
What is retroperitoneal?
Describe the steps in the positioning of the midgut.
(1) The ileum elongates and the midgut herniates into the umbilicus.
(2) The midgut undergoes a 90 degree counterclockwise rotation.
(3) The midgut retracts from the umbilicus and undergoes a 180 degree counterclockwise rotation.
(4) The ascending colon attaches to the body wall.
What gut structures are intraperitoneal?
Abdominal esophagus, stomach, gall bladder, jejunum, ileum, appendix, cecum, transverse colon, sigmoid colon.
What gut structures are secondarily retroperitoneal?
Duodenum, pancreas, ascending colon, descending colon.
What gut structures are retroperitoneal?
Thoracic esophagus, rectum.
What is a congenital omphalocele?
A herniation of the intestines into the umbilical cord due to a failure of midgut retraction.
What is an umbilical hernia?
A herniation of the intestines into the umbilical cord due to incomplete closure of the umbilicus.
What is gastroschisis?
An extrusion of midgut structures through the ventral body wall due to incomplete lateral folding.
What is Meckel's diverticulum?
When a remnant of the yolk stalk persists as an outpouching of the ileum. It may contain gastric or pancreatic tissue and can cause appendicitis-like symptoms.
What is midgut volvulus?
An aberrant twisting of the large intestine that can cause stenosis or atresia of any portion of the intestine.
Describe the formation of the rectum and urogenital sinus.
(1) The hindgut forms an expansion called the cloaca that is sealed by the cloacal membrane.
(2) The cloaca is divided into the rectum and urogenital sinus by the urorectal septum.
(3) The urorectal septum fuses with the cloacal membrane to form a urogenital membrane and an anal membrane separated by the perineum.
(4) Proliferation of the anal membrane forms the anal pit.
(5) The anal pit invaginates to form the anorectal canal.
What is the visible junction between the ectodermal and endodermal portions of the anorectal canal?
The pectinate line.
What is Hirschsprung's disease?
A dilation of a region of the colon due to a peristalsis defect caused by a failure of neural crest migration and enteric ganglion formation. Also called congenital megacolon.