Which veins are noted for lacking valves?

The common iliac veins are notably lacking valves, which is crucial for understanding venous anatomy and physiology. Valves in veins serve to prevent backflow and assist with venous return, particularly in the extremities where blood faces gravity. However, the common iliac veins, which are located deeper within the body, do not contain valves. This anatomical feature is significant as it reflects their role in draining blood from the lower limbs and pelvic region directly into the inferior vena cava without the resistance or potential for backflow that valves typically manage in other vein types.

In contrast, many veins in the body do contain valves, especially those in the lower limbs, to facilitate effective blood return against gravity. This includes the femoral veins and popliteal veins, which rely on valves to support venous return during physical activities. Superficial veins, while also containing valves, serve primarily in the drainage of the skin and subcutaneous tissues and communicate with deep veins, which may be more susceptible to conditions like varicose veins when valve function is compromised. Hence, recognizing the absence of valves in the common iliac veins underscores an important aspect of how blood circulates back to the heart from the lower body.