There are different types of blood vessels in the body. Based on their structure and function, blood vessels are classified as either arteries, capillaries, or veins. Arteries carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls.

Veins are the blood vessels that carry blood from the tissue of all the parts of the body back to the heart . Veins are also found all over the body which appears greenish blue because it carries deoxygenated blood in it.

Capillaries are the smallest and most numerous of the blood vessels. On reaching the tissues, arteries divide further into extremely thin tubes called capillaries. The capillaries join up to form veins which empty into the heart. The primary function of capillaries is the exchange of materials between the blood and tissue cells.