What is the primary function of the renal vein?

The primary function of the renal vein is to carry deoxygenated blood away from the kidneys. After the kidneys filter the blood, the renal veins collect this blood, which has had waste products removed and excess substances regulated, and return it to the systemic circulation. This is crucial because it ensures that the filtered blood can be returned to the heart and replenished with oxygen before being redistributed throughout the body.

In the context of the other choices, filtering excess waste is the job of the nephrons within the kidney, not the renal vein itself. Supplying oxygenated blood to the kidneys is the role of the renal arteries, which deliver blood rich in oxygen to support kidney function. Transporting nutrients to the kidneys is not specifically a function of the renal vein, as nutrients are typically delivered via blood that flows through the arteries. The primary role of the renal vein is clearly defined in facilitating the removal of deoxygenated blood after filtration has occurred.