The human body is a complex system of interconnected parts, and the circulatory system plays a crucial role in maintaining overall health. One key component of this system is the inferior vena cava, a large vein responsible for returning blood from the abdominopelvic viscera and abdominal walls to the heart.

The inferior vena cava is fed by numerous smaller veins. The lumbar veins, for instance, drain the posterior abdominal wall, emptying both directly into the inferior vena cava and into the ascending lumbar veins of the thoracic azygos system. The gonadal veins, which differ on each side of the body, also contribute. The right gonadal vein drains from the ovary or testis on the right side into the inferior vena cava, while the left gonadal vein drains into the left renal vein.

The kidneys are drained by the right and left renal veins. The adrenal glands, or suprarenal glands, also have their own veins. The right suprarenal vein empties into the inferior vena cava, while the left suprarenal vein drains into the left renal vein. The inferior phrenic veins, draining the inferior surface of the diaphragm, also play their part.

The common iliac vein forms by the union of the internal and external iliac veins. The internal iliac vein drains the pelvis and external genitalia, and the external iliac vein drains the lower abdominal wall anteriorly, the cremaster muscle in males, and external genitals and lower limbs.

Interestingly, some organs, such as the gastrointestinal tract, spleen, pancreas, and gallbladder, do not directly feed into the inferior vena cava. Instead, they pass their blood into the hepatic portal vein, which delivers the blood to the liver for processing. This processed blood then drains into the hepatic veins, which finally empty into the inferior vena cava.