Lecture 10: Development of the GI system Flashcards
Describe the development of the primitive gut (include days)
- Yolk sac and endodermal sheet precursor (day 20)
- Branches forming Foregut, midgut and hindgut forms from the sheet (day 24)
- branch to yolk sac also narrows and forms the vitelline duct (day 26)
What arteries are associated with the primitive gut?
Foregut - celiac trunk
midgut - SMA
hindgut - IMA
What organs come from the foregut?
Esophagus, stomach, liver, gallbladder, pancreas, upper duodenum (upper organs)
What organs come from the midgut?
most of the small intestines, ascending colon and proximal 2/3 of the transverse colon
What organs come from the hindgut?
distal 1/3 of transverse colon to anal canal
What parts of the GI tract/tube come from the endoderm?
mucosal epithelium and GI glands (except for lower 1/3 of anus)
What parts of the GI tract/tube comes from the splanchnic mesoderm?
Muscles, vessels and Ct
What parts of the GI tract/tube comes from the ectoderm?
ENS ganglia and nerves (NCC derived)
Epithelium of lower 1/3 of anus
When do the dorsal and ventral mesenteries develop?
Wk 4
What structures come from the dorsal mesentery (posterior wall connector)?
greater orementum (gastrosplenic, gastrocolic and splenorenal ligaments) small intestine mesentery Mesoappendix transverse mesocolon sigmoid mesocolon
What structures come from the ventral mesentery (anterior wall connector)?
lesser omentum -hepatoduodenal and hepatogastric ligaments, basically all the liver ligaments
What does intraperitoneal mean?
What does retroperitoneal mean?
What does secondary retroperitoneal mean?
- suspended by mesentery
- fused with the abdominal wall
- organs initially suspended by mesentery but has since fused with body wall
Describe the process of stomach rotation
Vagus innervation?
-Starts as a tube facing anteriorly, then rotates 90 to the left as dorsal mesogastrum enlarges leftward to form the greater omentum
-Ventral stomach on the left side (L. vagus n.)
Dorsal stomach on the right side (R. vagus n.)
Hypertrophic Pyloric Stenosis
Cause
Clinical
- NCC did not properly migrate so ENS not fully populated > missing ENS control of the sphincter so it cannot relax
- pyloric lumen narrowing causing obstruction of food passage, projectile vomiting, few BM, cannot gain weight
Describe how the liver develops and when does this happen?
Primitive gut endoderm develops the hepatic diverticulum > differentiation into hepatocytes/bile ducts and hepatic ducts (main liver) + gallbladder
Week 4-5
The splanchnic mesoderm of the primitive gut develops into which cells of the liver?
stromal, Kupffer and stellate cells
Describe how the pancreas develop and when does this happen?
-primitive gut develops the dorsal pancreatic bud and ventral pancreatic duct which grow into respective mesentery > dorsal and ventral buds fuse at wk 5
Day 30 - 35 (week 5)
Dorsal pancreas includes which parts?
Ventral pancreas includes which parts?
- head, body and tail of pancreas
- uncinate process
Annular pancreas
duodenal obstruction or stenosis
bilious vomitin if annulus is in the inferior bile duct, low birth weight
What are some anomalies in pancreatic development?
Accessory pancreatic duct Pancreas divisum (separated ducts, single pancreatic duct did not form - prone to pancreatitis)
How does the gallbladder form?
How does the bile duct form?
- ventral cystic diverticulum forms at Wk 5 and forms the gallbladder
- liver develops a closed bile duct that is reopened by reacanalization
Biliary atresia
Cause
Symptoms
- obliterated exta/intrahepatic ducts and are replaced by fibrotic tissues due to inflammation
- neonatal jaundice, white stool, dark urine, can be treated with liver transplant
How does the spleen develop and when does this happen?
Wk 4: mesenchyme condenses in the dorsal mesogastrium
Wk 5: spleen forms (mesoderm, not endoderm)
What is special about the development of the midgut?
Abdomen has limited size, so midgut herniates into the umbilicus as it lengthens between and returns back (Wk 10/Day 73)
Describe how gut (intestines) rotation occurs and when doe these happen?
Day 50: gut rotates CCW at 90 degrees > cecum and ascending colon end up on the left
Day 70: gut rotates CCW at 180 degrees > cecum at RUQ and ascending colon is anterior to duodenum
Day 77: Midgut returns back from herniation > cecum goes back to RLQ and ascending colon is dragged to the right abdomen
What are the retroperitoneal viscera at the end of GI development?
What are the secondary retroperitoneal viscera at the end of GI development?
- thoracic esophagus and rectum (entrance and exit)
- duodenum, pancreas, ascending and descending colon
- everything else is intraperitoneal
Omphalocele
-wall weakness after lateral body folding, allowing bowel to herniate through umbilicus with peritoneal covering
usually associated with Trisomy 13 or 18
Gastroschisis
abdominal wall herniation with no peritoneal covering
Meckel’s diverticulum
Cause
Clinical
- vitelline duct did not regress, leading to a pouch in the lower small intestine
- abdominal swelling, SB obstruction, sepsis, Gi bleeding
Non-rotation of midgut loop
Reverse gut rotation
-2nd CCW 180 rotation did not occur
left sided colon and right sided small intestines
-2nd 180 rotation is CW instead of CCW
transverse colon is behind duodenum
Volvulus
- rolled up twisted intestines
- acute AP, vomiting, GI bleed
Intestinal Stenosis and Atresia
- caused by ineffective recanalization (stenosis for partial obstruction, atresia for complete obstruction)
- commonly associated with Trisomy 21
Describe the fate of the cloaca (distal hindgut)
Urorectal septum develops infoldings that separate dorsal anorectal canal and ventral urogenital sinus
-cloacal membrane ruptures creating the exterior canal
Describe the development of the anal canal and the pectineal line
-anal rectal lumen has epithelial plug that closes it off > mesenchyme forms anal pit with ectodermal walls > apoptosis eventually opens the plug
Superior 2/3 of anal canal: endoderm
Inferior 1/3 of anal canal: ectoderm
(these 2 are divided by the pectineal line)
Imperforated anus
Persistent anal membrane
