GI Embryology Flashcards
Endoderm Contributions to GI Tract
Mucosal Epithelium and GI glands except for lower 1/3 anus
Mesoderm Contributions to GI Tract
Muscular Wall
Connective Tissue
Vasculature
Ectoderm Contributions to GI Tract
Enteric ganglia, nerves, glia (neural crest)
epithelium of lower 1/3 anus
Cranio-caudal folding of endoderm
- when
- what does it form
- special components
4th week: trilaminar disc to cylinder
- single tube of endoderm
- forms foregut, midgut, hindgut
- Vitelline Duct: narrowed opening to yolk sac
Foregut Derivative in GI
Esophagus to Upper Duodenum
- liver, pancreas, gallbladder
Midgut Derivative in GI
lower duodenum to splenic flexure
Hindgut Derivative in GI
splenic flexure to anal canal
Foregut arterial supply
celiac trunk
Midgut arterial supply
superior mesenteric artery
hindgut arterial supply
inferior mesenteric artery
Mesentery definition
double fold of peritoneum attaching intestines to abdominal wall
- prevent organs from floating around
Dorsal Mesentery
- which organs are derivatives
- connects organs to dorsal body wall
- greater omentum (gastrosplenic, gastrocolic, splenorenal ligaments)
- small intestine mesentery
- mesoappendix
- transverse mesocolon
- sigmoid mesocolon
Ventral Mesentery
- which organs are derivatives
-connects foregut to ventral wall from septum transversum to umblicial vein
- lesser omentum (hepatoduodenal, hepatogastric ligament)
- falciform , coronary, triangular ligament of liver
Intraperitoneal organs
suspended by mesentery
Retroperitoneal organs
excluded from peritoneal cavity
- SAD PUCKER
Secondarily retroperitoneal
initially suspended within mesentery but later fused with body wall
Foregut development: organs (6)
Esophagus stomach liver gall bladder pancreas upper duodenum
Describe Rotation of Stomach
1) Dilated of foregut endoderm
2) Rotates 90 degrees
- left side moves ventrally
- right side moves dorsally
- vagus nerve follows rotation ( left vagus on ventral stomach, right vagus on right stomach)
3) lesser sac posterior to stomach
4) dorsal mesogastrium enlarges to form greater omentum
Hypertrophic Pyloric Stenosis
- definition
- causes
- manifestation
- narrowing of pyloric lumen-> obstruction of food passage
causes:
- gradual hypertrophy of muscularis externa (thickened muscle)
- inability of sphincter to relax bc of faulty NCC migration
Manifestation
- mass at right costal margin
- non- bilous vomiting with feeding
- small stool
- can’t gain weight
exposure to erythromycin is associated with it
Liver Formation
- when
- germ layer
- components
week 4
- endoderm-> hepatocytes, bile duct, hepatic duct
- splanchnic mesoderm-> stromal cells, kuppfer cells, stellate cell
hepatic diverticulum
- endoderm
- connection of diverticulum to foregut= common bile duct
- hematopoietic organ
Gallbladder formation
- two components
1) Cystic diverticulum
- second outpouching of common bile duct
- from hepatic diverticulum
- cystic duct
- direct lumen recanalization
2) bile formation
- week 12
- hepatocytes
Biliary Atresia
- symptoms
- treatment
Obliteration of extrahepatic or intrahepatic ducts
- inflammation replaces duct with fibrotic tissue
Symptoms:
- progressive jaundice
- white colored stool
- dark urine
TX: liver transplant
Pancreas formation
- when
- describe location
week 5: rotation of stomach and migration of liver
Two buds from foregut inferior to cystic diverticulum (endodermal)
- have exocrine and endocrine parts
- Ventral pancreatic bud-> ventral mesentery
- Dorsal pancreatic bud-> dorsal mesentery
Ventral pancreatic duct, cystic duct, and common bile duct move posteriorly
Ventral duct fuse with dorsal duct
- main pancreatic duct: connection to duodenum and ventral pancreatic duct
- accessory pancreatic duct: remnants of dorsal duct to duodenum
Ventral pancreas fate
uncinate process, part of pancreatic head
Dorsal pancreas fate
pancreatic head, body, tail
Pancreas Anomalies (3)
1) Accessory Pancreatic Duct
2) Pancreas Divisum
- ventral and dorsal parts fail to fuse by week 8
- asymptomatic, abdominal pain
3) Annular pancreas
- poor migration of pancrease-> pancreatic ring around 2nd part of duodenum
- duodenal obstruction/stenosis
- BILOUS vomiting
- low birth weight
Spleen formation
- when
- derivative
Week 4: mesenchymal condensation in dorsal mesogastrium
Week 5: spleen form
** derived from mesoderm NOT endoderm
What are the derivatives of the midgut?
- lower duodenum (distal to bile duct)
- jejunum
- ileum
- cecum
- appendix
- ascending colon
- proximal 2/3 of transverse colon
What is the timeline of development of the midgut including rotation?
- midgut herniates out of umbilicus at week 6 (around day 50)
- 90 degree counterclockwise (CCW) rotation
- distal part develops cecum, proximal part becomes convoluted
- body and abdominal cavity grows and midgut returns (day 70)
- proximal returns first, passes under distal portion toward left (another 90 degree CCW)
- distal portion returns (another 90 degree CCW)
What is omphalocele?
- fetal abdominal wall defect
- 2.5/10,000 births
- herniation through umbilicus with peritoneal covering
- increased risk with trisomy 13 or 18
- etiology:
- herniated bowel does not fully retract
- failure of lateral fold closure –> wall weakness –> bowel herniation
- malformation of connective tissue of skin and hypaxial musculature of body wall –> wall weakness
What is gastroschiscis?
- herniation of abdominal contents through abdominal folds
- 3-4/10,000 births
- not covered by peritoneum
What is the difference between omphalocele and gastroschiscis?
omphalocele: covered in peritoneum
gatrochiscis: not covered by peritoneum
What is Meckel’s Diverticulum?
- incomplete obliteration of vitelline (omphalomesenteric) duct
- true diverticulum: all layers of bowel wall
- most common congenital anomaly of GIT
- rule of 2: 2x in males, 2 inches, 2 feet from ileocecal valve, 2% of population, 2 first years of life, 2 types gastric or pancreatic
- usually clinically asymptomatic
- abdominal swelling, obstruction, RLQ pain, GI bleed
Yolk stalk connection pathologies
- Meckel’s diverticulum
- umbilical sinus
- fibrous cord with immediate cyst
- umbilicointestinal fistula
- fibrous cord connecting SI to umbilicus
What is malrotation/nonrotation of midgut loop?
- completion of first 90 degree CCW rotation, but does not do remaining rotations
- results in left sided colon and right sided intestines
- 1/500 births
- complications: formation of fibrous Ladd bands can lead to volvulus duodenal obstruction
What is reverse gut rotation?
- completion of 90 degree CCW rotation followed by 180 degree CW rotation
- results in transverse colon posterior to duodenum
What is volvulus?
- complications
- symptoms
- when is there increased risk?
- twisting of bowel around its mesentery
- complications: obstruction and infarction
- symptoms: acute abdominal pain, vomiting, GI bleeding
- increased risk with gut rotation abnormalities
Describe intestinal lumen formation
- lumen temporarily obliterated due to endodermal proliferation
- vacuoles form as endodermal cells regenerate –> recanalization of lumen
What is duodenal stenosis?
partial occlusion of lumen due to incomplete recanalization
What is duodenal atresia?
failure to recanalize –> complete occlusion of lumen
-associated with trisomy 21 (down syndrome)
What is jejunal/ileal stenosis/atresia?
- due to vascular insufficiency
- prominent abdominal distension with ileal atresia/stenosis
What are the derivatives of the hindgut?
- distal 1/3 transverse colon
- descending colon
- sigmoid colon
- rectum
- superior 2/3 anal canal (to pectinate line)
Describe separation of cloaca
- urorectal septum partitions cloaca into dorsal anorectal canal and ventral urogenital sinus
- cloacal membrane ruptures –> opens urogenital sinus and anal canal to exterior
Upper 2/3 of anal canal
- germ layer
- blood supply
- innervation
- endoderm
- superior rectal A from IMA and superior rectal V to IMV –>portal V
- lumbar and pelvic splanchnic nerves
Lower 1/3 of anal canal
- germ layer
- blood supply
- innervation
- ectoderm
- inferior rectal A from pudendal A and inferior rectal V to internal pudendal V–>internal iliac V–>IVC
- pudendal N branches
What is imperforate anus?
- congenital defect
- opening to anus is missing/blocked due to persistent anal membrane
- 1/5000 births
- low, intermediate, high distinction - relative to levator ani muscles and pelvic bony landmarks
What is Hirschsprung’s disease?
AKA congeinital aganglionic megacolon
- 1/500 live births
- abscence of ganglionic plexus due to failure of NCC to migrate
- presentation
- intestinal wall hypertrophy proximal to aganglionic segment
- lack of peristalsis (colon fails to relax)
- abnormal colonic dilation/distension (megacolon)
- treatment: surgical removal or constricted distal segment
