Hello Thanks for query. Penis consists of two cylindrical bodies called Corpora Cavernosa This is erectile tissue that resembles like a foam or sponge .This erectile tissue is a bunch of tiny arterioles which carrying pure blood . Erection is a very complex process that involves nervous,vascular system. As soon as one is aroused sexually by tactile and visual sensation there are signals from the brain carried by parasympathetic system to these arterioles and through a series of chemical reaction enzymes are released resulting into relaxation of walls of these arteriole and they are filled with pure blood carried there by arteries .At the same time the walls of the veins of the penis which carry impure blood back to heart are blocked this results in trapping of blood in penis (Corpora Cavernosa).This trapped blood makes the penis hard and stiff what is called as Erection. The mucus glands located in urethra secrete excessive mucus which acts as a lubricant to helps to pass out the thick semen during ejaculation . Apert from semen and this mucus there are no other fluids in penis duering erection and Ejaculation. Hope this information will help you and serve your purpose . Dr.Patil.