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
Tail vein Tail vein Tail vein or caudal vein is the largest vein in vertebrate animals' tail. It leads directly into the posterior cardinal vein in the posterior trunk in fishes. Mammal caudal vein (the middle caudal vein) leads to inferior vena cava. Caudal vein is one of the many places from which a laboratory worker can withdraw blood from a mouse specimen. The process does not require the death of the mouse, that is, assuming that not too much more than the established standard of "no more than two blood samples are taken per session and in any one 24-hour period.".