The tubules through which the blood is circulated inside the body are called blood carrying vessels or blood vessels. These vessels are directly or indirectly connected with the heart.
The blood vessels are of three types, Artery, Vein and Capillary.
Artery: The vessels which carry oxygenated blood away from the heart to various organs of the body are called arteries.
Capillary: The aorta originates from the heart and then branches into extremely narrow arteries or arterioles. These branches further divide many times and form fine networks. Later these fine nets joining together form the vein. Arteries and veins are connected by those fine networks. These nets which connect the arteries and veins are called capillaries. The wall of the capillary is very thin. Its wall is formed by one layered thin epithelial cells, as a result, exchange can easily occur between the blood inside its cavity and the food juice and waste substance inside the cell.
Vein: The vessels which carry blood from various organs of the body toward the heart are called veins. Veins generally carry deoxygenated or carbondioxide enriched blood. But the pulmonary vein carries oxygenated blood from the lung to the heart. Veins originate from the capillaries. The main difference of artery and vein are given below on the table.