Sperm production

Sperm are produced, stored, and delivered by the male reproductive system. The male reproductive system includes the testes, urethra, vas deferens, prostate gland, seminal vesicle, and penis.

The testes contain coiled structures called seminiferous tubules, which are the sites of sperm production. They produce over 12 billion sperm per month. The epididymis lies on top of the seminiferous tubules. Immature sperm migrate from the seminiferous tubules to the epididymis to mature and be stored.

Before intercourse, the penis fills with blood and becomes erect. With sufficient stimulation, the ejaculatory process begins.

The mature sperm travel from the epididymis through the vas deferens. The vas deferens is a narrow, muscular tube about 18 inches long. Its smooth muscle contractions propel the sperm forward. They arrive first at the ampulla, the widest part of the vas deferens, and then pass into the ejaculatory ducts. In the ejaculatory ducts, a liquid secretion from the seminal vesicles mixes with the sperm. Seminal fluid contains fructose sugar, which the sperm use as fuel as well as alkalines, which help to counteract the naturally acidic environment of the vagina and uterus providing the sperm a better chance for survival.

The liquid mixture is propelled forward through the ejaculatory ducts toward the urethra, passing first through the prostate gland, where milky prostatic fluid is added, forming the substance we call semen. The prostatic fluid helps the sperm swim faster, which is important for getting to the egg cell.

Finally, about a teaspoon of semen is ejected out (ejaculated) through the far end of the urethra at the end of the penis. From the time the sperm leave the man' s body, they have between 12 and 48 hours to find and fertilize the egg cell, assuming an egg is available. Of the 300 million sperm ejaculated, only about 200 or so will survive to reach the egg cell and only one will succeed in fertilizing it.