Embryology of the upper GI tract Flashcards
Origin of the esophagus
lining/parenchyma - foregut endoderm
muscular coat - splanchnic mesoderm
Innervation of the esophagus
upper 2/3 - directly by vagus (striated)
lower 1/3 - vagus nerve via celiac plexus (smooth)
Origin of the stomach
lining - foregut endoderm
dorsal mesogastrium - mesoderm
ventral mesogastrium - mesoderm of the septum transversum (only seen in foregut)
Origin of the duodenum
foregut and midgut endoderm
Origin of the liver
parenchyma: foregut endoderm (cranial part of liver bud)
stroma (Kupffer cells, hematopoietic tissue) - mesoderm of septum transversum
gallbladder - foregut endoderm (caudal part of liver bud)
cystic and common bile ducts - foregut endoderm (stalk of liver bud)
Origin of the pancreas
caudal part of foregut endoderm (pancreatic buds)
Dorsal bud –> between two layers of the dorsal mesentery (most of pancreas)
Ventral bud –> between two layers of ventral mesentery, forms a part of the head
fusion of two buds
Origin of the spleen
mesoderm - mesenchymal cells between mesodermal layers of dorsal mesogastrium
Foregut derivatives
Esophagus, stomach
duodenum, proximal to the opening of the bile duct
liver, biliary apparatus and pancreas
Stomach development
FUsiform enlargement of the caudal part of the foregut
faster growing of the dorsal border (greater curvature)
ventral border - lesser curvature
90 degree clockwise rotation
Mesentery derivation
dorsal –> dorsal mesogastrium
ventral –> ventral mesogastrium
Liver development
between the two layers of the ventral mesogastrium
Congenital hypertrophic pyloric stenosis
thickening of the pylorus
hypertrophy of the muscular layers of the pylorus
pre-birth: polyhydramnios
post-birth: projectile vomiting
Duodenal stenosis
partial occlusion of the duodenal lumen, usually caused by incomplete recanalization of the duodenum
Duodenal atresia
complete occlusion of the lumen of duodenum
distention of the epigastric region on infants and vomiting begins within a few hours of birth - almost always contains bile
Polyhydramnios
Hepatic diverticulum
ventral outgrowth from the caudal part of the foregut
gives rise to the liver, gallbladder and biliary duct system
Caudal part –> gall bladder
Kupffer cell/hematopoietic tissue of the liver
mesenchyme in septum transversum
Ventral mesentery
lesser omentum (hepatogastric and hepatoduodenal ligaments)
falciform ligament
umbilical vein in the free border of the falciform ligament –> round ligament of the liver
main pancreatic duct
distal part of the dorsal pancreas and duct of the ventral pancreas
accessory pancreatic duct
proximal part of the dorsal pancreas
Foregut supplies
Celiac artery
Greater splanchnic nerve (T5-T9), sym
Para: vagus
Midgut
small intestine (most of duodenum) cecum, vermiform appendix, ascending colon, right half to right 2/3 of transverse colon
Midgut supply
superior mesenteric arter
Rotation of midgut
90 degree counterclockwise during protrusion
180 degree rotation during return to abdomen (10th week)
- small intestine first, then large intestine
Fixation of the intestines
rotation of the stomach and duodenum brings duodenum and pancreas to the right side –> pressed to the posterior abdominal wall (retroperitoneal) by colon
Ascending and descending colon also become retroperitoneal
Cecal diverticulum
primordium of the cecum and appendix - appears as as welling on the midgut
during descent of the diverticulum, cecum, colon and appendix form
Congenital omphalocoele
persistence of the herniation of the abdominal contents into the proximal parts of the umbilical cord
Nonrotation of the midgut
Left-sided colon
midgut loop does not rotate as it returns to the abdomen
SI on the right, colon on the left
Reversed rotation
midgut loop rotates clockwise rather than counterclockwise
duodenum anterior to SMA, transverse colon posterior to SMA
SMA can compress transverse colon
Subhepatic cecum and appendix
adhering of the cecum to the inferior surface of the liver as it returns to the abdomen
retains fetal position
Ileal/Meckel diverticulum
proximal portion of the yolk sac remains
sometimes becomes inflamed, mimics appendicitis
wall of the diverticulum may contain small patches of gastric/pancreatic tissue –> gastric mucosa often secretes acid
Umbilicoileal fistula
persistence of the entire intra-abdominal portion of the yolk sac
Duplication of intestines
During intestinal development - solid stage where intestine is full
Some vacuoles develop in the lumen –> hollow intestines
Failure of normal recanalization/duplication can occur (cystic, tubular)
Hindgut
left 1/3-1/2 of the transverse colon, descending colon, rectum, superior part of the anal canal
epithelium of the urinary bladder, most of the urethra
Hindgut supplies
inferior mesenteric artery
Cloaca
terminal dilated portion of the hindgut
in contact with surface ectoderm at the cloacal membrane
Cloacal memrane composed of endoderm of the cloaca + endoderm of the proctoderm/anal pit
Partitioning of the cloaca
Urorectal septum divides cloaca to ventral and dorsal parts
Urorectal septum fuses with the cloacal membrane –> dorsal anal membrane and a large urogenital membrane
Also divides the cloacal sphincter into the anterior and posterior parts
Anterior: muscles covering external genitalia erectile tissues
Posterior: external anal sphincter
Ectodermal depression - proctodeum/anal pit in the anal membrane
Anal canal
superior 2/3 hindgut
inferior 1/3 from proctoderm (ectoderm)
Upper 2/3 anal canal supply
nerve - autonomic
artery - superior rectal artery
venous - superior rectal (to portal system)
lymph - inferior mesenteric lymph nodes
Lower 1/3 anal canal supply
nerve - pudendal
artery - inferior rectal
venous - inferior rectal (to IVC)
lymph - inguinal lymph nodes
Congenital megacolon (Hirschsprung disease)
absence of autonomic ganglion in the myenteric plexus
