Stomach Development

Stomach development 1. Formation of the blank From the end of the fourth week, a fusiform dilatation of the middle part of the anteriorprimitive intestine appears. This dilation will evolve into the stomach. The mesos located atthis level of the digestive tract therefore take the name of ventral midgut and dorsal midgut.The gastric anlage increases rapidly in the abdominal region and will flatten transverselythen increase in an asymmetrical manner, more significant at the posterior edge than at theanterior edge. This creates a large curvature and a small curvature of the stomach. 2. Rotations Subsequently, a double rotation will bring the stomach into its final anatomical position: A first rotation of 90° around a longitudinal axis in clockwise brings the posterior edge (largecurvature) to the left and the anterior edge (small curvature) to the right. The phrenic nervewhich passed on the lateral aspects of the stomach is now positioned on the anterior andposterior aspects. The second rotation takes place around a dorsoventral axis and causes a movement of thecephalic part of the primordium (cardia and fundus) down and to the left while the caudalpart (pylorus) moves up and to the right. 3. Evolution of the ventral and dorsal midguts The rotation of the stomach causes the movement of the ventral and dorsal midguts as wellas the organs located there (the liver in the ventral midgut and the spleen in the dorsalmidgut). The very significant development of the hepatic anlage towards the right causes therotation of the stomach around its longitudinal axis and the displacement of the spleentowards the left. The dorsal midgut lengthens and partially attaches to the posterior wall ofthe abdomen. This lengthening and rotation of the stomach leads to the appearance of a foldin the peritoneal cavity behind the stomach: the omental bursa. The ventral midgut, in which the liver develops, will give rise to the falciform ligament whichconnects the liver to the abdominal wall, the peritoneal covering around the liver (except atits upper pole in contact with the diaphragm) and the small omentum which connects theliver to the stomach (hepato-gastric ligament) and the duodenum (hepato-duodenalligament). The dorsal midgut will give rise to the gastrosplenic ligament which connects thestomach to the spleen and the splenorenal ligament connecting the spleen to the posteriorwall at the level of the kidney. Following the rotation of the gastric anlage around its dorsoventral axis, the dorsal midgutcontinues its development downwards and forwards thus forming a pocket below thestomach which covers the colon and the intestinal loops and whose two layers willsubsequently fuse to form the large omentum (which will subsequently fuse with thetransverse mesocolon).

4. Development of the duodenum The duodenum is made up of two segments on either side of the hepatic anlage: the portionlocated upstream of the liver bud derives from the most distal segment of the primitiveforegut; the portion located downstream of the liver bud derives from the proximal segmentof the midgut. The “U” shape of the duodenum results on the one hand from both thedevelopment of the hepatic anlage and the rotation of the stomach which lead to a shifttowards the right of the duodenal frame and on the other hand from the growth of the headof the pancreas. Due to the modification of the position of the mesos following rotation of thestomach, the mesoduodenum finds itself pressed against the posterior wall of the peritonealcavity and its layers end up fusing with the peritoneum. The duodenum thus becomes aretroperitoneal organ except for a short portion which follows the pylorus.