Sperm are the smallest cells in a man's body. They look like microscopic tadpoles. A sperm is made up of a head, a midsection, and a tail. The head of the sperm contains the genetic material. Each sperm, when fertilized with an egg, contains enough genetic material to form a human being. The midsection provides energy and nourishment for the sperm. The tail is used to propel the sperm along the reproductive tract. The head of the sperm is covered by a protective structure called an acrosome.

The acrosome contains essential enzymes that give the sperm their ability to penetrate the egg's surface and fertilize it.

Sperm Production

The early sperm cells that begin to develop within the testicles are primitive and do not yet have tails. These developing sperm remain within the testicles for a little more than two months. During that time, they grow and develop into more mature sperm. At the end of this time, the almost fully developed sperm move on to the epididymis. The still developing sperm will use the next several weeks within the epididymis to become fully formed and capable of fertilization. This entire sperm production cycle takes about 90 to 100 days. Thus every three months or so, a man produces an entirely fresh new quota of sperm. If a supply of old sperm was never ejaculated, it will simply be absorbed by the body.

Sperm Ejaculation

Approximately 100 million sperm are released during a normal ejaculation. Medical research indicates that about 90 percent of these sperm are killed by vaginal secretions. Even if sexual intercourse occurs under the best possible conditions, only a few hundred or a few thousand sperm actually make it through the cervix, into the uterus, and up one of the fallopian tubes. Of those sperm, about half will swim up the wrong fallopian tube. (That is, the egg is waiting in the other fallopian tube.) Therefore, of the millions of sperm ejaculated, there may be only 100 or so candidates available to fertilize the egg. If no egg is present, some sperm may stay in the fallopian tube and wait. In these conditions, some sperm may live for about 12 to 20 hours; some experts claim that the sperm may live up to 72 hours.

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