Which part of the vena cava collects most venous blood from organs inferior to the diaphragm?

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The main idea is that venous return from below the diaphragm goes to the heart primarily through the inferior vena cava. This large vein collects blood from many sources below the diaphragm—kidneys via the renal veins, the gonads, lumbar and pelvic veins, and the lower limbs via the iliac veins. Blood from the digestive organs does drain via the hepatic portal system to the liver first, but after it’s processed, it leaves the liver through hepatic veins into the inferior vena cava, contributing to the overall return. The superior vena cava handles blood from the upper body, and the umbilical vein is a fetal vessel. So, the inferior vena cava is the vessel that collects most venous blood from organs inferior to the diaphragm.