The middle rectal artery is a branch of the anterior division of the internal iliac artery Controversy is associated with the contribution of the middle rectal artery. The size and presence of the middle rectal artery may be in inverse relationship to the superior rectal artery. As a practical matter, a particularly small superior rectal artery may be an indication during a low anterior resection that the middle rectal arteries are substantial. Less controversial is the paucity of vascular supply to the anterior and particularly posterior aspects of the rectum from the superior rectal artery. The extent of crossover of vascular supply between the inferior and superior rectal arteries is also debated however it is accepted that the rectum and anus can survive ligation of the superior and middle rectal arteries.
Venous drainage follows the main arterial supply.
Reflexes Rectoanal inhibitory reflex and Inflation reflex Rectal distention and electrical stimuli induce relaxation of the internal anal sphincter with a resultant lowering of the resting pressure. The internal anal sphincter recovers within one minute from small volumes of air or stool. . The rectoanal inhibitory reflex is absent in Hirschsprung's disease, Chagas disease, and after rectal mucosal excision. It may return after initially being abolished by a low rectal anastomosis. The afferent receptors are therefore not only in the anorectal epithelium and rectal wall, but probably also in the pelvic floor.