Stomach rotation and the lesser and greater curvatures
In the embryo, the stomach's front edge swings right to form the short lesser curvature (a curved border), and its back edge swings left to form the long greater curvature.
Remember
Think front and back: the front edge turns to the right and ends up as the lesser curvature, while the back edge turns to the left, grows faster and ends up as the greater curvature.
Memory aid
the front edge goes right and stays little, while the back edge goes left and grows big
Pair the front edge with right and little, and the back edge with left and big.
The stomach starts as a straight tube, a slightly widened part of the foregut (the upper part of the early gut tube). It has a front edge, the ventral border, and a back edge, the dorsal border. Each edge is tied to the body wall by a mesentery (a double fold of peritoneum, the thin membrane lining the abdomen).
The tube then turns through about 90 degrees around its long axis, which lies along the length of the tube. The ventral border swings round to the right and becomes the short lesser curvature. The dorsal border swings round to the left and becomes the long greater curvature.
The two curvatures end up different in length because the dorsal side grows faster than the ventral side. A second turn, known as the anteroposterior (front-to-back) rotation, then pulls the end of the tube that continues towards the duodenum upwards, which gives the classic shape of the stomach.
Sheets of peritoneum called omenta attach to the curvatures. The lesser omentum (a thin double sheet of peritoneum) links the lesser curvature to the liver, and the greater omentum hangs from the greater curvature.
Key facts
- Ventral border
- swings to the right and becomes the lesser curvature.
- Dorsal border
- swings to the left and becomes the greater curvature.
- The turn
- about 90 degrees around the long axis of the tube.
- Growth
- the dorsal side grows faster, so the two curvatures end up different in length.
- Lesser omentum
- links the lesser curvature to the liver.
- Greater omentum
- hangs from the greater curvature.
Exam traps
- The dorsal border does not become the lesser curvature, because it swings to the left and forms the greater curvature.
- The right wall of the tube does not become the lesser curvature. The lesser curvature ends up on the right because the ventral border swings to the right.
- Faster growth of the ventral wall does not make the greater curvature, because the ventral wall is the slower-growing border and becomes the lesser curvature.
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