The structure indicated is the inferior vena cava.

The inferior vena cava is responsible for carrying deoxygenated blood into the right atrium of the heart from the lower part of the body. The inferior vena cava is formed at the point of union of the right and left common iliac veins at the L5 vertebral level.

Several veins drain into the inferior vena cava:

• Lumbar veins
• Right gonadal vein (the left gonadal vein drains into the left renal vein)
• Renal veins
• Right suprarenal vein
• Inferior phrenic vein
• Hepatic veins

The inferior vena cava ascends through the abdomen immediately anterior to the vertebral column on the right side, adjacent to the abdominal aorta which sits on the left.

Learn more about the veins of the body in this tutorial.