Guess what I still remember from Health class? The pituitary gland controls sexual organ functions, and it's located around the brain area (base of the skull, according to Wikipedia). Having said that, I don't know if the pituitary would take those duties as seriously if there was no semen to spread around (AH HA HA HA).
I'd do more research, but I'm scared of what the Internet might show me, plus, I'm at work.