Stomach

Origin: Endodermal

• Lower part of foregut, swelling appears
• Anterior border connected to anterior abdominal wall by ventral mesogastrium
• Posterior border connected to posterior abdominal wall by dorsal mesogastrium
• Posterior border grows more – forms greater curvature of stomach
• Anterior border forms lesser curvature
• Stomach then rotates 90 degrees clockwise (due to growth of liver)
• So dorsal mesogastrium forms lesser sac
• Liver develops in ventral mesentery – mesentery becomes lesser omentum
• Spleen develops in dorsal mesentery – mesentery becomes gastrosplenic ligament

Clinicals: Congenital hypertrophy of pyloric sphincter – narrows pyloric canal. More common in males.

NB: Development of stomach and rotation causes right vagus nerve to become posterior vagus trunk. Left vagus nerve becomes anterior vagus trunk

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Duodenum

Origin: Endodermal

• Distal foregut and proximal midgut
• Form a “C” shaped loop projecting ventrally
• Due to stomachs rotation 90 degrees clockwise
• Duodenal loop carried dorsally and to the right, becomes adherent to posterior abdominal wall
• Mesentery of duodenum disappears except in the 1st and 4th part (ligament of trietz)
• The lumen is temporarily obstructed and canalized again

Congenital anomalies:

1. Incomplete canalization/ atresia – green vomit, no bowel movement
2. Incomplete fixation to posterior abdominal wall – sites of internal hernia

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Pancreas

Origin: 2 endodermal buds form:

1. Endoderm of dorsal wall of duodenum – dorsal pancreatic bud
2. Endoderm of ventral wall of duodenum from hepatic bud stem – ventral pancreatic bud

• Dorsal pancreatic bud arises slightly above liver bud, extends dorsally and upwards into mesoduodenum
• Ventral pancreatic bud migrates dorsally to lie below and behind dorsal bud
• The 2 buds fuse together (ventral bud – head and uncinate process)
• Ducts of the 2 buds join – main pancreatic duct
• Islets of Langerhans appear – insulin secretion begins in 5th month

Congenital anomalies:

1. Annular pancreas – develops as a ring around 2nd part duodenum
2. Ectopic pancreatic tissue – eg. wall of duodenum, jejunum, ileum or stomach