Blood vessels
Blood vessels are pipelines that carry blood, and can be divided into arteries, veins, and microvessels according to transport directions. Arteries from the heart of the blood to the body tissue, the vein from the blood tissue back to the heart, microvascular connect arteries and veins, blood and tissue material exchange between the main places. Various types of organisms have different types of blood vessels. Open circulation biological, such as insects, only arteries. Blood flow out of direct contact with the body tissue, and then by the heart of the hole to recover the blood. A closed organ, such as a mammal, a bird, a reptile, a fish, is connected to the vein by the arterial microvessel and finally to the heart. ...