Blood circulating from the left side of the heart to body tissues and back to the heart is travelling in the blood vessels.
Indeed, the oxygenated blood goes from the heart to the body tissues through the blood vessel with different diameters:
Aorta: is the big artery which came out from the heart.
Artery, and arterioles: which have a shorter diameter
Capillaries: which has the shortest diameter, this is where nutrient and oxygen are distributed.
Then the blood goes back to the heart by venules, veins, and vena cava.
All the bold words are blood vessels
