The pelvic blood supply primarily comes from the internal iliac artery, which branches off from the common iliac artery. This artery supplies blood to the pelvic organs, including the bladder, reproductive organs, and rectum. Veins in the pelvis, such as the internal iliac vein, drain blood from these organs and return it to the inferior vena cava. The pelvic blood supply is crucial for maintaining the health and function of the organs within the pelvic cavity.