Veins of the pelvis

The patterns of the portal and systemic (vena caval) venous systems of the abdominopelvic cavity are shown. Venous drainage from pelvic organs flows mainly to the caval system via the internal iliac veins. The upper rectum normally drains into the portal system, although the superior rectal veins anastomose with the middle and inferior rectal veins, which are tributaries of the internal iliac veins.