mesentery

The mesentery proper attaches the jejunum and ileum to the posterior abdominal wall, running obliquely from the duodenojejunal junction (left upper quadrant, near L2) to the ileocecal junction (right lower quadrant, near the right sacroiliac joint). It is a fan-shaped fold containing the superior mesenteric artery and vein, lymphatics, lymph nodes, and autonomic nerve fibers, all supported by connective tissue and fat between its two peritoneal layers. The mesentery is now recognized as a contiguous organ (per Coleman/Calvin research), rather than a series of separate fragments, extending from the duodenum to the rectum. Clinically, the mesentery is important in several contexts: (1) Volvulus - twisting of bowel around its mesenteric root can cause vascular compromise and ischemia; (2) Mesenteric ischemia - occlusion of the SMA (embolism, thrombosis) leads to bowel infarction, presenting with pain out of proportion to exam; (3) Mesenteric lymphadenitis - inflammation of mesenteric lymph nodes, often mimicking appendicitis in children (frequently due to Yersinia enterocolitica); (4) Mesenteric cysts and tumors (e.g., carcinoid tumors causing desmoplastic reaction); (5) Internal hernias can occur through mesenteric defects; (6) Superior mesenteric artery syndrome - compression of the third part of duodenum between the SMA and aorta. Understanding the root of the mesentery and its relationship to other peritoneal structures (mesocolon, omenta) is essential for understanding referred pain patterns, spread of infection/malignancy along peritoneal reflections, and surgical anatomy.