Embryology of the upper GI tract

Question 1

Origin of the esophagus

Answer 1

lining/parenchyma - foregut endoderm

muscular coat - splanchnic mesoderm

Question 2

Innervation of the esophagus

Answer 2

upper 2/3 - directly by vagus (striated)

lower 1/3 - vagus nerve via celiac plexus (smooth)

Question 3

Origin of the stomach

Answer 3

lining - foregut endoderm
dorsal mesogastrium - mesoderm
ventral mesogastrium - mesoderm of the septum transversum (only seen in foregut)

Question 4

Origin of the duodenum

Answer 4

foregut and midgut endoderm

Question 5

Origin of the liver

Answer 5

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)

Question 6

Origin of the pancreas

Answer 6

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

Question 7

Origin of the spleen

Answer 7

mesoderm - mesenchymal cells between mesodermal layers of dorsal mesogastrium

Question 8

Foregut derivatives

Answer 8

Esophagus, stomach
duodenum, proximal to the opening of the bile duct
liver, biliary apparatus and pancreas

Question 9

Stomach development

Answer 9

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

Question 10

Mesentery derivation

Answer 10

dorsal –> dorsal mesogastrium

ventral –> ventral mesogastrium

Question 11

Liver development

Answer 11

between the two layers of the ventral mesogastrium

Question 12

Congenital hypertrophic pyloric stenosis

Answer 12

thickening of the pylorus
hypertrophy of the muscular layers of the pylorus
pre-birth: polyhydramnios
post-birth: projectile vomiting

Question 13

Duodenal stenosis

Answer 13

partial occlusion of the duodenal lumen, usually caused by incomplete recanalization of the duodenum

Question 14

Duodenal atresia

Answer 14

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

Question 15

Hepatic diverticulum

Answer 15

ventral outgrowth from the caudal part of the foregut
gives rise to the liver, gallbladder and biliary duct system
Caudal part –> gall bladder

Question 16

Kupffer cell/hematopoietic tissue of the liver

Answer 16

mesenchyme in septum transversum

Question 17

Ventral mesentery

Answer 17

lesser omentum (hepatogastric and hepatoduodenal ligaments)
falciform ligament
umbilical vein in the free border of the falciform ligament –> round ligament of the liver

Question 18

main pancreatic duct

Answer 18

distal part of the dorsal pancreas and duct of the ventral pancreas

Question 19

accessory pancreatic duct

Answer 19

proximal part of the dorsal pancreas

Question 20

Foregut supplies

Answer 20

Celiac artery
Greater splanchnic nerve (T5-T9), sym
Para: vagus

Question 21

Midgut

Answer 21

small intestine (most of duodenum)
cecum, vermiform appendix, ascending colon, right half to right 2/3 of transverse colon

Question 22

Midgut supply

Answer 22

superior mesenteric arter

Question 23

Rotation of midgut

Answer 23

90 degree counterclockwise during protrusion
180 degree rotation during return to abdomen (10th week)
- small intestine first, then large intestine

Question 24

Fixation of the intestines

Answer 24

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

Question 25

Cecal diverticulum

Answer 25

primordium of the cecum and appendix - appears as as welling on the midgut during descent of the diverticulum, cecum, colon and appendix form

Question 26

Congenital omphalocoele

Answer 26

persistence of the herniation of the abdominal contents into the proximal parts of the umbilical cord

Question 27

Nonrotation of the midgut

Answer 27

Left-sided colon midgut loop does not rotate as it returns to the abdomen SI on the right, colon on the left

Question 28

Reversed rotation

Answer 28

midgut loop rotates clockwise rather than counterclockwise duodenum anterior to SMA, transverse colon posterior to SMA SMA can compress transverse colon

Question 29

Subhepatic cecum and appendix

Answer 29

adhering of the cecum to the inferior surface of the liver as it returns to the abdomen retains fetal position

Question 30

Ileal/Meckel diverticulum

Answer 30

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

Question 31

Umbilicoileal fistula

Answer 31

persistence of the entire intra-abdominal portion of the yolk sac

Question 32

Duplication of intestines

Answer 32

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)

Question 33

Hindgut

Answer 33

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

Question 34

Hindgut supplies

Answer 34

inferior mesenteric artery

Question 35

Cloaca

Answer 35

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

Question 36

Partitioning of the cloaca

Answer 36

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

Question 37

Anal canal

Answer 37

superior 2/3 hindgut | inferior 1/3 from proctoderm (ectoderm)

Question 38

Upper 2/3 anal canal supply

Answer 38

nerve - autonomic artery - superior rectal artery venous - superior rectal (to portal system) lymph - inferior mesenteric lymph nodes

Question 39

Lower 1/3 anal canal supply

Answer 39

nerve - pudendal artery - inferior rectal venous - inferior rectal (to IVC) lymph - inguinal lymph nodes

Question 40

Congenital megacolon (Hirschsprung disease)

Answer 40

absence of autonomic ganglion in the myenteric plexus