Blood vessel vessels function to transport blood. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system Oxygen (bound to hemoglobin in red blood cells) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95–100%) with oxygen. In all veins apart from the pulmonary vein, the saturation of hemoglobin is about 75%. (The values are reversed in the pulmonary circulation.) In
Azygos vein and usually occurs simultaneously with situs inversus, asplenia, or polysplenism, persistent left superior vena cava (SVC), and congenital pulmonary venolobar syndrome. Azygos and hemiazygos continuation of the IVC is rare especially when it is not associated with congenital heart disease. The Greek root "zyg" refers to a pair. 'A-' means "not". Thus, "azygos" means "unpaired". The azygos vein is unpaired in that there is only one in the body, mostly on the right side. While there is the hemiazygos vein and its accessory on the left side of the body, they are considered tributaries of the azygos vein rather than