Vein cells called tunica intima. The precise location of veins varies much more from person to person than that of arteries. Veins serve to return blood from organs to the heart. Veins are also called "capacitance vessels" because most of the blood volume (60%) is contained within veins. In systemic circulation oxygenated blood is pumped by the left ventricle through the arteries to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries. After taking up cellular waste and carbon dioxide in capillaries, blood is channeled through vessels that converge with one another to form
Lumbar veins Lumbar veins The lumbar veins are veins running along the inside of the posterior abdominal wall. They are the lumbar equivalent of the posterior intercostal veins. They are four in number and accompany the four lumbar arteries, with the vein lying superior to the artery (the same arrangement as in the intercostal neurovascular bundles). The first and second lumbar veins usually join the ascending lumbar vein rather than the inferior vena cava, which then joins the subcostal vein of the same side to form the azygous vein on the right or hemiazygous vein on the left. The third and fourth