## Dorsal Mesentery and Mesenteric Root Formation **Key Point:** The dorsal mesentery of the midgut becomes the **root of the mesentery** after rotation, attaching obliquely from the duodenojejunal flexure (left upper quadrant) to the ileocecal junction (right lower quadrant). ### Mesenteric Attachment Changes | Phase | Mesenteric Attachment | Orientation | |-------|----------------------|-------------| | **Pre-rotation** | Vertical line from pylorus to ileocecal junction | Dorsal midline | | **Post-rotation** | Duodenojejunal flexure to ileocecal junction | Oblique (left to right, superior to inferior) | | **Final state** | Root of mesentery | ~6 cm long, crosses L2–L3 vertebra | **High-Yield:** The oblique orientation of the mesenteric root after rotation explains why: - Jejunal loops lie on the left side of the abdomen - Ileal loops lie on the right side - The root is a natural barrier during abdominal surgery ### Peritoneal Fusion After rotation, secondary retroperitoneal fusion occurs: - Ascending colon fuses to posterior peritoneum (right side) - Descending colon fuses to posterior peritoneum (left side) - Duodenum becomes retroperitoneal - BUT the mesentery itself is **NOT resorbed** — it persists as the root of the mesentery **Clinical Pearl:** The oblique mesenteric root is clinically important because it defines the plane of potential volvulus and guides surgical dissection during abdominal procedures. [cite:Moore's Clinically Oriented Anatomy 8e] 
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