The renal veins are veins that drain the kidney. They connect the kidney to the inferior vena cava. They carry the blood purified by the kidney. There is one vein per kidney, that divides upon entering the kidney.
Because the inferior vena cava is on the right half of the body, the left renal vein is generally the longer of the two.
Because the inferior vena cava is not laterally symmetrical, the left renal vein often receives the following veins:
left inferior phrenic vein
left suprarenal vein
left gonadal vein (left testicular vein in males, left ovarian vein in females)
left 2nd lumbar vein