81. The Foregut: The Omental Bursa and Duodenum

  1. The omental bursa (lesser peritoneal sac)
    1. CLEFTS develop between the cells of the dorsal mesogastrium which coalesce and eventually form a single cavity, the omental bursa
      1. The cavity expands in all directions and comes to lie behind the stomach and to the right of the esophagus
      2. The upper portion of the cranial extension of the sac is limited by the developing diaphragm, to form closed space or sac called the infracardiac bursa
      3. The lower portion of the cranial extension of the sac persists as the superior recess of the lesser sac
      4. As the stomach enlarges, the lesser sac expands into an inferior recess which forms between the layers of the elongating dorsal mesogastrium (greater omentum)
        1. The 4-layer greater omentum overhangs the developing small intestines
        2. Most of the inferior recess of the lesser sac disappears as the layers of the greater omentum fuse
      5. The omental bursa communicates with the main peritoneal cavity or greater peritoneal sac by way of the epiploic foramen or foramen of Winslow
  2. The duodenum forms from the terminal portion of the foregut and the cephalic or cranial portion of the midgut
    1. THE 2 PARTS grow rapidly and form a C-shaped loop that projects ventrally
      1. The junction of the foregut and midgut is at the apex of this embryonic loop, just distal to the origin of the liver bud
    2. AS A RESULT OF ITS DUAL ORIGIN, the duodenum is supplied by branches of both the celiac and superior mesenteric arteries
    3. AS THE STOMACH ROTATES, the duodenum rotates to the right and comes to lie retroperitoneally
    4. DURING WEEKS 5 AND 6, the duodenal lumen is reduced and temporarily may even be obliterated by epithelial cells. However, under normal conditions, the lumen recanalizes by the end of the embryonic period
    5. A GREAT PORTION OF THE VENTRAL MESENTERY of the duodenum disappears. The free border of this mesentery which does remain lies between the duodenum and the liver and forms the ventral border of the epiploic foramen and the duodenohepatic ligament. This mesentery is also a portion of the so-called lesser omentum

the foregut:  the omental bursa and duodenum: image #1