What vein is responsible for draining blood from the lower half of the body into the heart?

The inferior vena cava is the vein responsible for draining blood from the lower half of the body back to the heart. It collects deoxygenated blood from the lower extremities, pelvis, and abdomen, and transports it to the right atrium of the heart. This is crucial for maintaining proper circulation, ensuring that blood returning from the lower parts of the body can be reoxygenated in the lungs.

The superior vena cava, while also a significant vein, specifically drains blood from the upper half of the body, including the head, neck, arms, and chest, and does not play a role in draining the lower half.

The femoral vein is involved in draining blood from the thigh and leg, but it does not capture blood from the entire lower half of the body, as it is just one of many veins that contribute to the inferior vena cava.

The renal vein drains blood from the kidneys and does not have any role in collecting blood from the lower body, focusing instead on the renal (kidney) region. Therefore, the inferior vena cava is the appropriate choice for the question regarding the drainage of blood from the lower half of the body into the heart.