Birth :

Mesentery is centered by the superior mesenteric artery (a. Mesenterica Superior) emerging on the anterior face of aorta in regard of T12-L1.

Route :

Its origin is retroperitoneal, retropancreatic, and then, it passes in front of the small pancreas of Winslow (uncinatus processus), crosses the left renal vein and the third duodenum and becomes intra mesenteric. (figure 11) This artery goes within the mesentery downward, forward and right on about 25 centimeters and ends 60 to 80 centimeters upstream the ileocaecal angle in regard of the vestige of the omphalo mesenteric canal (Meckel's diverticulum).

This artery describes a descreet concavity on the right and back; its caliber ranges from about 12 mm at its origin to 2 mm in its end.

Extra mesenteric portion :

- branches destinated to pancreas and duodenum (aa. pancreatico-duodenales superior right and inferior left, a. of the duodeno jejunal angle) .

Intra mesenteric portion :

One describes separately the right and left hand collaterals due to their different embryonic origins.

- Right branches destinated to colon are few : a.colica dextra, a. colica media, a. ileocolica, a. appendicularis. They are located in the right mesocolon.

- Left branches are more numerous (12 to 16), highly anastomosed, forming arches of 1st to nth order (5 or 6). They are destinated to the small bowel and located in the mesentery.

Terminal branches:

The last order of arches is parallel to the mesenteric edge of the bowel and is called consequently "parallel vessel" (of Dwight). This "parallel vessel", gives birth to the multiple straight vessels (vasa recta) which plunge into the serous layer and vascularize the mucosa. Each vasa recta gives two collaterals for each face of the bowel.

Figure 12: Vascular elements in periphery of mesentery (anatomic sample)
1 Small bowel covered with peritoneum (on certain parts, note the continuity with mesentery)
2 Mesentery
3 Last order arch
4 Anterior straight artery
5 Straight vein