The major circuit
The blood circuit responsible for transporting blood to the cells of the body is called the major circuit, through which the oxygenated blood leaves the heart through the aortic artery, which branches off to form a network of capillaries that reach all tissues. On this journey, the blood leaves oxygen and nutrients in the cells, while in turn picks up carbon dioxide and cellular waste, and returns to the heart to complete the cycle.
The way in which the circulatory system is made up, from the heart to the tissues and then from the tissues to the hearth again is as follows (from larger to smaller diameter of the vessels):
Heart - aorta artery - arteries - arterioles - capillaries - tissues - venules - veins - vena cava - heart.
Arteries are those blood vessels that transport oxygenated blood, while veins are those that transport carbo oxygenated blood.