They are microscopic - 500 million sperm would fit in a teaspoon. Each sperm cell has 23 chromosomes - the genetic material carrying all the man's inherited characteristics. From puberty on, sperm are continuously produced in the testes. When sperm become mobile, their tails move like whips, propelling them forward. They move in to the epididymis, where they remain to mature for about two weeks.
Mature sperm leave the epididymis and enter the vas deferens.
These tubes pass through the seminal vesicles and the prostate gland, which secrete fluids that mix with the sperm to provide nourishment and increase motility. This mixture of fluids and sperm is called semen. The semen travels through the penis and out of the body by way of the urethra, the same tube that carries urine. In response to physical or emotional stimulation, more blood than usual flows into the blood vessels of the penis. As a result, the penis becomes larger and harder and stands away from the body.