Mesentery

The root of the mesentery is only about 15 cm long. It runs obliquely from the duodenojejunal flexure, left of L2, down to the right sacroiliac joint and ileocaecal junction. On its way it crosses the 3rd part of the duodenum, the aorta, the IVC, the right ureter, the right psoas and the right gonadal vessels. Its intestinal border is several metres long, matching the length of the jejunum and ileum, so the mesentery is pleated like a fan. Between its two layers lie the jejunal and ileal branches of the SMA with their arcades and vasa recta, tributaries of the SMV, lacteals, about 100–200 mesenteric lymph nodes, the superior mesenteric autonomic plexus, and fat, which increases towards the ileum.

Other parts of the gut have their own mesenteries: the transverse mesocolon, the sigmoid mesocolon, the mesoappendix, and the mesorectum around the rectum. Recent anatomical work describes the mesentery as a single continuous organ from the duodenojejunal flexure to the mesorectum. On this view the ascending and descending mesocolons persist, flattened against the posterior wall by fusion fascia (Toldt). This concept underpins complete mesocolic excision in colorectal cancer surgery.