Blood travels through blood vessels from arteries to capillaries to veins. The heart pumps the blood under pressure, but the strong blood vessels are all capable of withstanding this. The arteries' job is to carry red, oxygenated blood away from the heart. The largest artery is called the aorta. It is an artery that has a diameter of 25 mm. The arteries eventually get smaller and turn into arterioles.
This is where the blood goes into capillaries. Capillaries are like trading stores. Oxygen, nutrients, and glucose diffuse into the walls. What also happens here, is the carbon dioxide and other wastes diffuse into the cells.
At the end, the blood becomes deoxygenated and goes into the venules, and then the veins. Finally, through the veins, blood is pumped back to the heart.