During embryological development, the midgut undergoes rotation around the superior mesenteric artery. Which is the most common direction and degree of rotation in normal gut development?

Explanation

## Normal Midgut Rotation: Direction and Degree **Key Point:** The midgut rotates **270° counterclockwise** around the SMA as the primary axis during weeks 6–10 of gestation. ### Three Phases of Rotation | Phase | Timing | Degree | Key Event | |-------|--------|--------|----------| | **Phase 1** | Weeks 6–8 | 90° counterclockwise | Duodenum moves posteriorly; cecum moves superiorly | | **Phase 2** | Weeks 8–10 | 180° counterclockwise | Cecum descends to right lower quadrant; small bowel loops to left | | **Phase 3** | Week 10+ | Final positioning | Cecum reaches RLQ; duodenojejunal junction fixed at ligament of Treitz | | **Total** | — | **270° counterclockwise** | Normal anatomical position achieved | ### Anatomical Consequences of 270° Rotation 1. **Duodenum** becomes retroperitoneal (C-shaped loop, posterior to SMA). 2. **Jejunum and ileum** occupy the left and central abdomen. 3. **Cecum** settles in the right lower quadrant. 4. **Ligament of Treitz** forms at the duodenojejunal junction, anchoring the midgut. **Mnemonic:** **"LDR"** = **L**eft (small bowel on left), **D**uodenum (retroperitoneal), **R**ight (cecum on right) — the end result of 270° counterclockwise rotation. **High-Yield:** Any deviation from 270° counterclockwise (e.g., 90°, 180°, or clockwise) results in malrotation with risk of volvulus and obstruction. [cite:Langman Embryology 14e Ch 11]