What is the male penis actually comprised of? blood vessels and muscle?

Lots of things: Blood vessels, muscle, fat, connective tissue, nerves -- the same stuff that makes up all the other organs in your body. Also sugar and spice and everything nice.

Very little muscle: Contrary to what most men would like to believe, the penis is a pretty non-muscular organ. It is comprised almost entirely of a sponge like material that holds blood. With an erection, blood flows into the sponge and can't get out because valves shut and prevent the blood from draining out. The sponge becomes so full of blood that it becomes hard. After climax, the valves open and the blood goes.