Sagittal Cross-Section of Lower Male Trunk
If you look up near the top of the illustration, you can see the left common iliac vein. The common iliac vein consists of both the internal and external iliac veins, which consist of the small veins and capillaries that connect to the intestines. This is the blood in your body that supplies you with nutrients - the acids and enzymes in the human digestive tract break down food into molecules small enough to pass through the wall of the intestine. When blood flows down to the lower abdomen, it drops off oxygen where it’s needed, and picks up the broken-down nutrients, before flowing to the organs where the nutrients will be processed, through the inferior vena cava. [De-oxygenated blood returns to the heart via the superior vena cava, not inferior.]
Applied Surgical Anatomy, Regionally Presented, for the use of students and practitioners. George Woolsey, 1902.