Describe how the penis becomes prepared for insertion into the vagina.
Sexual excitement, which stimulates the nerves of the autonomic system, causes the veins in the penis to constrict and the arteries to dilate. The arteries carry a great volume of blood under significant pressure into the penis. The blood fills the spaces within the penis's spongy, erectile tissue of which the penis is largely composed. The engorged tissue causes the penis to become greatly increased in size. As a result, the penis becomes hard and erect, prepared for insertion into the female vagina.
