There are three types of blood vessels in the human body, which can be divided into arteries, veins and capillaries. Arteries are the vessels that carry blood from the heart through various levels of branches and finally to the lungs or tissues, the end of which is connected to capillaries. Veins refer to the vessels that are connected to capillaries and then converge at various levels, gradually becoming thicker vessels and then returning blood to the heart, which are characterized by inelasticity, thin walls and thick lumen compared to arteries veins. Capillaries are the blood vessels that connect arteries and veins, and capillaries are in the shape of a network, and are the parts of the blood where gases and substances are exchanged.