Which vein carries oxygen-poor blood from the legs and abdomen to the right atrium?

• A. Inferior vena cava
• B. Superior vena cava
• C. Portal vein
• D. Renal vein

Answer: (D)

The main idea is that deoxygenated blood from the lower body returns to the heart through a large vein that enters the right atrium. This vessel collects blood from the legs and abdomen by receiving blood from the common iliac veins, then travels upward through the abdomen, passes through the diaphragm, and empties into the right atrium. The portal vein, while a major venous conduit, carries nutrient-rich blood from the digestive organs to the liver, not directly to the heart. The renal veins drain the kidneys into the large vein that collects blood from the lower body, but they aren’t the route that brings all leg and abdominal blood to the heart. The vessel that does that specific job is the inferior vena cava.