[Vascularization of the anal canal]

The arterial blood supply of the anal canal derives from the superior, middle and inferior rectal arteries, whose branches reach the anal submucosa. Three main arterial trunks in the right anterior, right posterior and left lateral positions can be isolated below the pectinate line. They come, for the most important part, from the superior rectal artery. On the course of the anal submucosal venous plexus are fusiform, saccular or serpiginous dilatations confined to the lower half of the anal canal. This plexus is mainly tributary of the superior rectal vein to the portal system and secondly, of the middle and inferior rectal veins and the lateral sacral veins to the inferior vena cava. Arterio-venous direct communications have been demonstrated by serial section and by radiography of cadaveric specimens and by selective inferior mesenteric arteriography in patients. The erectile property of the anal submucosa as suggested by large vascular spaces, arterio-venous shunts and glomic systems may function in the erectile mechanism.