The male reproductive cells, the sperm, are manufactured in the testicles. Once mature, the sperm swim along a small tube called the vas deferens for storage in two small pouches called the seminal vesicles, situated just below the prostate gland. Both the vas deferens and the seminal vesicles produce a white sticky fluid in which the sperm are suspended.
When a man has an orgasm at the climax of sexual arousal, vigorous contractions are triggered in the muscular walls of the vas deferens, seminal vesicles and prostate, as well as rhythmic contractions of the muscles at the base of the penis. The sperm-filled fluid, called semen, is pushed into the urethra, passing through the prostate, where it collects more fluid, down the length of the penis to the tip from which it is ejaculated. There may be as many as 500 million sperm in one ejaculation.