Thurber RS 1- Development of the GI Tract Flashcards
What happens if body folding goes wrong?
Gastroschisis: Intestines lie outside of body
Ectopic Cardia
Epispadias: Bladder exits through the stomach
Exstrophy of the bladder: Skin over the lower bladder does not form properly
What is a thyroglossal duct cyst? How is it different from a brachial cyst?
The thyroglossal duct pulls the thyroid down from the tongue to its final position. If it does not obliterate, it becomes a midline cyst (as opposed to brachial cysts which are lateral).
What are the derivatives of the ventral mesentary? What parts of the gut is it associated with?
The ventral mesentery is only associated with the foregut and gives rise to the falciform ligament (connects the liver to the anterior abdominal wall), lesser omentum (made up of the hepatoduodenal ligament and hepatogastric ligament
What are the derivatives of the dorsal mesentery? Which parts of the gut is it associated with?
The dorsal mesentery is associated with the foregut, midgut and hindgut. It gives rise to the dorsal mesogastrum (greater omentum), dorsal mesoduodenum, mesentery proper and dorsal mesocolon
What is the difference between intraperitoneal, retroperitoneal and secondarily retroperitoneal?
Intraperitoneal is completely covered by viscera
Retroperitoneal is only covered by viscera at the front while the back is connected to the posterior abdominal wall.
Secondarily retroperitoneal means that it begins intraperitoneal, but becomes retroperitoneal by the end of development
What is a double bubble sign? What pathologies may cause it?
A double bubble sign is indicative of a dilation between the proximal duodenum and stomach.
It can be caused by annular pancreas, volvulus, intussusception, and duodenal atresia (complete closure or lack of part of the duodenum).
What is annular pancreas?
The pancreas forms from a ventral and dorsal bud off of the common bile duct. This ventral bud becomes the uncinate process, part of the head, and most proximal part of the main pancreatic duct. If this wraps around the duodenum, non-bilious vomit may occur
What are the 4 pathologies discussed that may occur if the 6th week midgut herniations do not occur properly?
Reversed rotation: The second 180* rotation that occurs when then intestines return to the abdominal cavity occurs clockwise instead of counter-clockwise. This causes the transverse colon to be posterior to the duodenum instead of anterior.
Left-sided colon: If the midgut does not rotate at all when it herniates from the abdominal cavity, it will result in the colon being on the left and the small intestine being on the right.
Omphalocele: If the midgut does not return to the abdominal cavity after it herniates, the bowel will remain herniated through the umbilicus.
Volvulus: A malrotation or twisting of the intestines can cause the blood vessels to become twisted, resulting in necrosis as well as death of the fetus.
What is the vitelline duct? What is the persistence of this structure?
The vitelline duct is a connection between the ileum and the yolk sac. If it does not obliterate 3 different pathologies may occur
Vitelline cyst: Intestines may become wrapped around this cyst, causing a volvulus
Vitelline fistula: Contents of the intestine can pass through the umbilicus
Meckel’s Diverticulum: An outpouching of the ileum
Where does the enteric nervous system arise from?
What happens if the ENS fails to develop?
The ENS arises from neural crest cells.
Failure of the ENS to develop can result in Hirschsprung Disease, a condition in which there are too few ENS neurons that leads to the newborn being unlikely to pass their first stool.
What is the pectinate line? How are internal and external hemorrhoids different with respect to pain sensation?
The pectinate line is where the ectoderm of the anal pit and endoderm of the hindgut meet.
External hemorrhoids are on the outside around the anus, while internal hemorrhoids are inside the anal canal.
Innervation above the pectinate line is visceral, which is why internal hemorrhoids are not painful.
Innervation below the pectinate line is somatic, which is why external hemorrhoids are painful.
What happens if the endoderm-derived GI tract does not end at the pectinate line? What types of anomalies may you expect to see?
Rectovaginal and urorectal fistulas
Failure of the urorectal septum to develop properly is the reason this happens. Because the urorectal septum does not form properly, the cloaca is not completely divided into the urogenital sinus and anorectal canal.
Imperforate anus
The anal pit and endoderm hindgut do not meet. The urorectal septum developed properly. However, the anal membrane (cloacal) fails to obliterate, such that there is not continuity between the endoderm-derived GI and ectoderm-derived GI tract.
What is the blood supply to the foregut, midgut and hindgut?
Foregut: Branches of the celiac artery
Midgut: Branches of the Superior mesenteric artery
Hindgut: Branches of the Inferior mesenteric artery
What structures does the endoderm give rise to?
Epithelium of the GI tract
Hepatocytes, endocrine and exocrine cells of the liver and pancreas
What structures does the Lateral Plate Mesoderm give rise to?
The visceral mesoderm gives rise to the spleen, while the parietal mesoderm gives rise to body wall membranes
