Development of GI Flashcards
What does the foregut make?
Oral cavity, pharynx, lower respiratory tract, esophagus, stomach, liver, gallbladder, pancreas, upper duodenum
What does the midgut make?
Lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal 2/3 of transverse colon
What does the hindgut make?
distal 1/3 transverse colon, descending colon, sigmoid colon, rectum, upper anal canal
What supplies blood to the foregut distal to the diaphragm?
celiac trunk
What supplies blood to the midgut?
superior mesenteric artery
What supplies blood to the hindgut?
inferior mesenteric artery
What are the beginning and end of the primitive gut tube?
Oropharyngeal membrane
Cloacal membrane
What connects the gut tube to the yolk sac?
vitelline duct
What makes the epithelial lining and glands of the GI tract, excluding the lower 1/3 anus?
endoderm
What makes the CT, vasculature and SM walls of the GI tract?
splanchnic mesoderm
What makes the epithelium of the lower 1/3 anus and NCC that make enteric ganglia, nerves and glia of GI tract?
ectoderm
When does maturaiton of the GI tract begin?
8 weeks
When does peristalsis occur?
10 weeks
What are the secondary retroperitoneal organs?
ascending colon
descending colon
duodenum
bulk of pancreas
When do the ventral and dorsal mesenteries form?
4th week
What does the ventral mesentery form?
lesser omentum
- –> hepatoduodenal L
- –> hypogastric L
falciform L
coronary L
triangular L
—>both of liver
Where does the ventral mesentery form?
between the body wall and foregut and between the diaphragm and umbilicus
Where does the dorsal mesentery form?
suspends diaphragm between lower esophagus to caudal hindgut
What does the dorsal mesentery make?
Greater omentum
- ——> gastrosplenic L
- ——-> gastrocolic L
- ——-> splenorenal L
SI mesentery
Transverse mesocolon
Sigmoid mesocolon
What makes the SI mesentery?
dorsal mesentery
What makes the transverse mesocolon?
dorsal mesentery
What makes the sigmoid mesocolon?
dorsal mesentery
What makes the greater omentum?
dorsal mesentery
What makes the lesser omentum?
ventral mesentery
What makes the falciform L?
ventral mesentery
What makes the coronary L of the liver?
ventral mesentery
What makes the triangular L of the liver?
vental mesentery
What makes R and L vagal nerves turn into Posterior and Anterior vagal trunks?
stomach rotation in development
What mesenteries is the stomach suspended by prior to rotation?
ventral and dorsal mesenteries
Describe rotation of stomach during development
Elongates, rotates 90 degrees so ventral mesentery is RIGHT and dorsal mesentery is LEFT
What is the portion of mesentery between the stomach and body wall after stomach rotation?
dorsal mesogastrium
What becomes the double-layered apron drape that eventually turns into the greater omentum?
dorsal mesogastrium
What does the stomach rotation make in terms of sacs?
lesser sac behind stomach
greater sac is continuous with abd cavity
Describe hypertrophic pyloric stenosis
pyloric lumen narrows and obstructs food passage
–>muscularis external hypertrophies and makes olive at the R costal margin
What is the etiology behind pyloric stenosis?
sphincter can’t relax d/t faulty NCC migration
—>ENS isn’t populated correctly
What are sx of pyloric stenosis?
non-bilious vomiting
few and small stools
can’t gain weight
What makes liver stromal, Kupffer and stellate cells?
splanchnic mesoderm
What is the embryonic hematopoietic organ?
liver
What organ has rare congenital abnormalities?
liver
When does bile begin to form?
week 12
Describe liver formation
diverticulum from gut ENDODERM buds–> grows into septum transversum–> differentiates into hepatocytes, bile duct and hepatic ducts
What percent of the population has an accessory pancreatic duct?
33%
What is pancreatic divisum?
two totally separate ducts, prone to pancreatitis
What are you prone to having if you have pancreatic divisum?
Pancreatitis
Where do the first endodermal buds of the pancreas form?
dorsal bud in dorsal mesentery
ventral bud in ventral mesentery
Do dorsal and ventral buds of the pancreas have exo/endo fxns?
Yes
When does the ventral pancreatic bud move to fuse with the dorsal bud?
5th week
What does the dorsal pancreatic bud form?
head, body and tail
What does the ventral pancreatic bud form?
unicate process
What occurs in an annular pancreas?
ventral bud wraps around the duodenum instead of completely migrating to the dorsal bud
What does annular pancreas cause?
duodenal obstruction/stenosis
BILIOUS vomiting if inferior to bile duct
What is the origin of the gallbladder and bile duct?
cystic endoderm
Describe how the bile duct forms
initially closed, opens via recanilization
Define biliary atresia
obliteration of the extra-/intra-hepatic ducts–>replaced with fibrous tissue d/t inflammation
What are the hallmarks of biliary atresia?
progressive jaundice soon after birth
white clay stools
dark urine
What is the treatment for biliary atresia?
liver transplant within 12-19 months of life
When does the spleen begin to develop?
4th week
Where does the spleen begin to form?
as a mesenchymal condensation in the dorsal mesogastrium
What is the spleen populated by during development?
mesoderm populated by myeloid lymphoid cells
What are the stages of herniation and re-entry of the midgut during development?
herniates out umbilicus at 6 weeks
comes back in at 10 weeks
Describe midgut rotation
1: 90 degree counterclockwise rotation
——> cecum and asc colon on L side of abd cavity
2: 180 degree counterclockwise rotation as it reenters abdomen
——-> cecum in RUQ, asc colon anterior to duodenum
3: rest of midgut enters abdomen
——–> cecum RUQ, pulls asc colon down to R side
——–> transverse colon in front of duodenum and
pancreas
Describe an omphalocele
herniation of gut continues out of the umbilicus
**covered with peritoneum
What causes an omphalocele?
- bowel doesn’t fully retract
- abnormal lateral body folding and fusion creates weakness in wall–>herniates
- CT of skin and hypaxial M of body wall dont form–>weakness–>herniation
Describe gastroschisis
herniation of abdomen contents through abd wall
–>not covered by peritoneum so exposed to external environment
Describe Meckel’s Diverticulum
vitelline duct doesn’t degenerate–>midgut still connected to umbilicus
List the rule of 2’s related to Meckel’s Diverticulum
2% incidence 2x more common in males 2% have medical sx 2 feet proximal to terminal ileum 2 inches long 2 years of age
What are the sx of Meckel’s Diverticulum?
abdominal swelling
SI obstruction
bowel sepsis
GI bleeding
Describe volvus
rolled up and twisted intestines
What do midgut rotation anomalies increase the risk of?
volvus
What are sx of gut volvus?
acute abdominal pain
omiting
GI bleeding
What are Trisomy 13 and 18 associated with?
omphalocele
What occurs in non-rotation of midgut loop?
only completes the first 90 degree counterclockwise rotation (not the 180)
What are the effects of non-rotation of midgut loop?
L sided colon, R sided SI
What occurs in a reverse gut rotation?
completes the first 90 degree counterclockwise rotation but then does a 180 degree rotatoin CLOCKWISE
—>so only net 90 degree clockwise rotation
What are the effects of reverse gut rotation?
transverse colon is posterior to duodenum
What are the sx of reverse gut rotation?
ischemia
stenosis of colon
Describe intestinal stenosis and atresia
partial occlusion/ ineffective recanalization of intestines OR complete occlusion
Why are the intestines closed during the 5-6th months?
endoderm proliferation causes the lumen to close–>recanalizes later
What is trisomy 21 associated with?
intestinal stenosis/atresia
What does the urorectal septum divide the cloaca into?
dorsal anorectal canal
ventral urogenital sinus
The cloaca ruptures after septum proliferates to give _______________
urogenital membrane and anal membrane
- ->sinuses open to exterior
- -> septum become perineum b/t urogenital and anus
What is the function of the anal plug?
temporarily closes anal rectal lumen
–>anal pit with ectodermal walls d/t mesenchymal proliferation
What is the anal canal made of?
2/3 endodermal epithelium (BV, N of hindgut)
1/3 ectodermal epithelium (BV, N of anal pit)
What BV supply upper anal canal?
superior and middle rectal As
What BV supply lower anal canal?
inferior rectal A
What divides the hindgut and anal pit?
pectineal line
What is the difference between anal canal and anal pit?
anal canal is the hindgut and anal pit
anal pit is lower anal canal that butts up to anus
What is an imperforated anus?
persistent anal membrane
What disease is due to a lack of ganglionic plexus (failure of NCC migration)?
Hirschsprung’s disease
List possible consequences of abnormal urorectal septum development
Persistent anal membrane Anal atresia Anoperineal fistula Rectovaginal fistula Rectourethral fistula Rectovesical fistula
