An extensive collateral circulatory system exists between the systemic and splanchnic vascular networks
The several systemic-splanchnic and intersplanchnic collateral channels that connect the three major mesenteric arteries and their branches become apparent in the event of occlusion of one of the major branches.
• Pancreaticoduodenal arcade provides collateral channels between the celiac axis and SMA (the superior pancreaticoduodenal arteries of the celiac axis collateralize with the inferior pancreaticoduodenal arteries of the SMA).
• Marginal artery of Drummond, composed of branches of the SMA and IMA, is a continuous arterial pathway that runs parallel to the entire colon.
• The middle colic branch of the SMA and the left colic branch of the IMA are connected by the arc of Riolan.
• The IMA connects with the systemic circulation via the iliac artery by the ileomesenteric arcade.
• A slowly developing occlusion promotes the opening of these collateral channels; thus chronic mesenteric arterial insufficiency (e.g., abdominal angina) is unusual unless there is virtually complete occlusion of two of the three major mesenteric arteries, including the SMA.