Blood circulation goes in a circle, which makes sense, given its name. Arteries carry blood away from the heart, and veins return blood to the heart. With one exception, blood carried away from the heart is oxygenated blood, and blood returning in the veins is de-oxygenated. The pulmonary circulation is the exception. Blood vessels from all areas of the body branch out to return blood to the heart, but they all flow eventually into the two great veins, the superior and inferior vena cava.
Superior Vena Cava
The superior vena cava returns blood from the head and upper extremities to the heart so it can be re-oxygenated. The superior vena cava drains into the right atrium; from there it goes to the right ventricle, which pumps it back to the lungs. The superior vena cava is created by the intersecting of the left and right brachiocephalic veins, formed from the subclavian and jugular veins, and the azygous vein, which drains part of the chest, abdomen and esophagus.
Inferior Vena Cava
The inferior vena cava carries oxygen-poor blood up from the lower extremities and major organs to the heart for re-oxygenation. Because the pressure in veins is lower than it is in arteries, and because venous blood returning to the heart is often working against gravity, the larger veins contain valves that keep the blood from back flowing when you stand or when your arms hang down. Branch veins are frequently named for the bones they're found near, South Dakota State University explains. The iliac veins, found near the iliac crest, join to form the inferior vena cava.
Pulmonary Veins
The pulmonary vein is the one exception to the rule that veins transport de-oxygenated blood. The blood in the pulmonary vein is oxygenated blood transported directly from the lungs to the left atrium of the heart. From the atrium, it passes into the left ventricle, and is then pumped out to supply the entire body with oxygenated blood.
Coronary Veins
The coronary aterial circulation supplies the muscles and tissues of the heart with oxygenated blood, then returns it directly to the right atrium via the coronary veins. Small coronary veins called venules join together to form veins, which drain into the coronary sinus, the main collection area for blood from the heart, according to the University of Minnesota.
