Why is the left renal vein longer than the right renal vein?

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Human kidneys — renal system Diagram showing the location of the kidneys in the abdominal cavity and their attachment to major arteries and veins.

The left renal vein is longer than the right renal vein because the inferior vena cava is positioned closer to the right kidney than to the left.1

Because the inferior vena cava runs along the right side of the abdominal cavity, the right renal vein has a shorter distance to travel to reach it. In contrast, the left renal vein must cross the midline of the body to reach the inferior vena cava, resulting in a greater length. Additionally, while the right renal vein typically receives blood exclusively from the kidney, the left renal vein also collects blood from other organs.12