What do the common iliac veins unite to form?

The common iliac veins unite to form the inferior vena cava, which is a major vein that carries deoxygenated blood from the lower half of the body back to the heart. Each common iliac vein drains blood from the respective leg and pelvic region. When they come together, they create the inferior vena cava at the level of the fifth lumbar vertebra.

This connection is crucial for the proper circulation of blood, as the inferior vena cava serves as a critical pathway for blood to return to the right atrium of the heart. Understanding the anatomy and function of these veins is essential in the study of systemic circulation and its importance when considering various conditions that may affect venous return, such as deep vein thrombosis or varicose veins.

Other choices do not relate directly to the common iliac veins: the superior vena cava drains the upper body, the portal vein is involved in the blood supply from the digestive organs to the liver, and the azygos vein provides an alternate drainage route for the thoracic cavity but does not connect with the common iliac veins.