Development of the GI system Flashcards
What embryonic germ layer do the foregut, midgut, and hindgut form from?
endoderm
what is the narrow opening to the yolk sac referred to as?
vitelline duct
what does the endoderm contribute to the GI tract?
mucosal epithelium and GI glands (except the lower 1/3 of the anus)
what does the splanchnic mesoderm contribute to the GI tract?
connective tissue, vasculature, and smooth muscle wall
what does the ectoderm contribute to the GI tract?
enteric ganglia, nerves, and glia (via neural crest) and the epithelium of the lower 1/3 of the anus
what is the arterial supply of the foregut?
the celiac trunk
what is the arterial supply of the midgut?
superior mesenteric artery
what is the arterial supply of the hindgut?
inferior mesenteric artery
what arises from the foregut?
esophagus, stomach, liver, gallbladder, pancreas, upper duodenum
what arises from the midgut?
lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 of the transverse colon
what arises from the hindgut?
distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, and upper anal canal
what is the abdominopelvic cavity lined with?
peritoneum
what does the dorsal mesentery give rise to?
the greater omentum, small intestine mesentery, mesoappendix, transverse mesocolon, and the sigmoid mesocolon
what does the ventral mesentery give rise to?
lesser omentum, falciform ligament of liver, coronary ligament of liver, triagnular ligaments of liver
what is the general description of intraperitoneal organs?
they are suspended by mesentery
what is the general description of retroperitoneal organ?
they are excluded from the peritoneal cavity
what are secondary retroperitoneal organs?
they were initially suspended within mesentery that later fused with a body wall
what are some examples of secondary retroperitoneal organs?
ascending/descending colon, duodenum, and bulk of pancreas
what are the retroperitoneal organs?
suprarenal glands, aorta/IVC, duodenum (2nd and 3rd parts), pancreas, ureters, colon (ascending and descending), kidneys, Esophagus, rectum
When the stomach rotates 90 degrees, how will the left side be positioned?
it will be ventral
when the stomach rotates 90 degrees, how will the right side be positioned?
it will be dorsal
the rotation of the stomach also causes the vagus nerve to rotated. The left vagus nerve will be positioned how after 90 degrees of rotation?
anteriorly
the rotation of the stomach also causes the vagus nerve to rotate. The right vagus nerve will be positioned how after 90 degrees of rotation?
posteriorly
where does the lesser sac sit?
behind the stomach
what ligaments make up the lesser omentum?
the hepatoduodenal ligament and the hepatogastric ligament
what causes hypertrophic pyloric stenosis?
faulty migration of neural crest cells–> ganglion cells of enteric nervous system not properly populated
what is hypertrophic pyloric stenosis?
inability of the pyloric sphincter to relax- narrowing of the pyloric lumen between the stomach and the duodenum
how does hypertrophic pyloric stenosis present?
palpable mass (OLIVE) at the right costal margin, projectile non-bilious vomiting after feeding, within a few months after birth
When does the stomach/liver form?
week 4 of development
what does the formation of the liver begin as?
hepatic diverticulum from the gut endoderm
what is the connection of the diverticulum to the foregut?
the common bile duct
what does the endoderm of the liver give rise to?
hepatocytes, bile ducts, and hepatic ducts
what does the splanchnic mesoderm in the liver give rise to?
stromal cells, Kupffer, and stellate cells
when does hematopoiesis in utero begin? and where does it occur?
by week 10 and in the liver
what does the gallbladder begin as?
cystic diverticulum
what does the cystic diverticulum come off of?
the common bile duct
what is the connection between the cystic diverticulum and the common bile duct called?
the cystic duct
when is bile formed by the hepatic cells?
beginning of week 12
what is biliary atresia?
obliteration of the bile duct/ inflammation replaces the duct with fibrotic tissue
what is the presentation of biliary atresia?
immediate onset of progressive jaundice in infants, white colored stool, dark urine
how does pancreas formation begin?
as two endodermal buds sprouting from the foregut inferior to the cystic diverticulum- the ventral and dorsal pancreatic bud
what does the ventral pancreatic bud give rise to?
the uncinate process of the pancreas
what does the dorsal pancreatic bud give rise to?
the pancreatic head, body, and tail
when does the ventral pancreatic bud migrate posteriorly to fuse with the dorsal pancreatic bud?
week 5
after rotation and fusion, what does the ventral pancreatic duct become?
the main pancreatic duct
what happens to the dorsal pancreatic duct after rotation and fusion?
it will disintegrate or if it remains it is known as an accessory pancreatic duct
what is pancreas divisum?
it is when the ventral and dorsal parts fail to fuse by week 8
what are patients with pancreas divisum prone to?
it is mostly asymptomatic, but they are prone to abdominal pain and pancreatitis
what is annular pancreas?
poor migration of the pancreas–> there is a pancreatic ring around the 2nd part of the duodenum
how does annular pancreas present?
duodenal obstruction/stenosis, bilious vomit, low birth weight
when does the spleen begin formation?
week 4
where does the spleen begin formation and as what?
as a mesenchymal condensation that forms in the dorsal mesentery
when is the spleen fully formed?
week 5
what is the spleen derived from?
from mesoderm NOT endoderm
when does the midgut herniate out from the umbilicus?
week 6
when does the midgut return to the abdomen?
by week 10
what does the proximal portion of the midgut loop do after it makes a 90 degree counterclockwise rotation outside of the abdomen?
it is now on the right and it becomes convoluted
what happens to the distal portion of the midgut loop after it makes a 90 degree counterclockwise rotation outside of the abdomen?
it is on the left and it develops the cecum
What ligaments make up the great omentum?
the gastrosplenic, gastrocolic, and splenorenal ligaments
what day does the gallbladder begin developing?
day 26
where does the gallbladder grow into?
the ventral mesentery
What happens with the midgut at week 6 of development?
it herniates out of the umbilicus and makes a 90 degree counterclockwise rotation
what happens to the midgut during the 10th week of development?
the proximal portion of the loop returns, passing under the distal portion- makes a second 90 degree counterclockwise turn
what is the positioning of the midgut during the 10th week of development?
the cecum is in the upper right quadrant and the ascending colon is anterior to the duodenum
what happens to the midgut during the 11th week of development?
the distal portion of the loop returns, making a 3rd 90 degree counterclockwise turn
what is the positioning of the midgut after the 11th week of development?
the cecum descends to the right lower quadrant, carrying the ascending colon to end up on the right side of the abdomen
what is an omphalocele?
a herniated bowel through the umbilicus that does not fully retract
what is an omphalocele covered with?
parietal peritoneum
who is at risk for having an omphalocele?
there is an increased risk with trisomy 13 or 18
what is gastroschiscis?
when there is an abnormal lateral body folding and fusion- so it creates wall weakness that allows the bowel to herniate
what does not form normally in a patient with gastroschiscis?
the connective tissue of skin and hypaxial musculature of body wall
what is the main difference between omphalocele and gastroschiscis?
with omphalocele, the herniated bowel is covered with parietal peritoneum; with gastroschiscis, the herniation is not covered by parietal peritoneum
what is meckel’s diverticulum?
failure of the yolk stalk (vitelline duct) connect to the midgut to regress- the midgut remains connected to the umbilicus
what is the presentation of Meckel’s diverticulum?
usually asymptomatic; rule of 2s: 2x more likely in males, presents in first 2 years of life
what is malrotation/non-rotation of the midgut loop?
the midgut loop completes the first 90 degree CCW turn, but does not do the remaining 180 degree CCW turn
what is the presentation of a malrotation/non-rotation midgut loop?
there is a left-sided colon and right sided small intestines; formation of fibrous Ladd bands
what can fibrous ladd bands lead to?
volvulus or duodenal obstruction
what is reverse gut rotation?
the midgut loop complete the first 90 degree CCW turn, but then does a 180 clockwise turn resulting in a 90 degree clockwise turn of the midgut loop
what is the presentation of a reverse gut rotation?
the duodenum ends up anterior to the transverse colon
what is a volvulus?
twisting of bowel around its mesentery
who is at an increased risk for developing a volvulus?
people with gut rotation anomalies
what is the presentation of a volvulus?
acute abdominal pain, vomiting, GI bleeding; coffee bean sign
what could a volvulus lead to?
bowel obstruction or infarction
what is the cloaca?
its a portion of the hindgut in the early embryo that separates into the rectum and the urogenital sinus
how is the cloaca divided?
by the urorectal septum
what is the cloaca divided into?
the ventral urogenital sinus and the dorsal anorectal canal
what is the anal rectal lumen temporarily closed by?
an endodermal epithelial anal plug- it eventually opens up via apoptosis
what germ layer makes up the rectum?
endoderm
what is the vasculature of the rectum?
the superior rectal (from the IMA) and the middle rectal (from the internal iliac artery) arteries; veins of hindgut
what germ layer makes up the anus?
ectoderm
what is the vasculature of the anus?
inferior rectal arteries (from the pudendal artery) and veins
what is the pectineal line?
it divides the origin of hindgut and anal pit within the anal canal
what is an imperforate anus?
when the opening of the anus is missing/blocked due to persistent anal membrane
what is hirschsprung’s disease?
failure of neural crest cell migration–> there is an absence of ganglionic plexus; lack of peristalsis (the colon fails to relax)
what is the presentation of hirschsprung’s disease?
intestinal wall hypertrophy proximal to the aganglionic segment; abnormal colonic dilation or distention (megacolon); failure to pass meconium
