Arterioles can be differentiated from arteries by the numbers of layers of smooth muscle. Usually there are no more than 6 layers. You can count the rows of nuclei to differentiate an artery and arteriole. How many smooth muscle cell layers can you see in the following photograph which shows two arterioles. Note the variation in size of the two vessels.
Capillaries are tiny vessels lined by a single layer of endothelial cells.
Note, in the following photograph, that one capillary accomodates only one blood cell. This helps you see why reducing the size of blood cells is important for their transport. Veins Find veins in your skin slide. Veins are distinguished by their thinner wall, valves, collapsed state. The tunica media does not look as well organized as that in the artery or arteriole.