The Male Reproductive System

The male reproductive system is also under the influence of hormones and is responsible for producing sperm. The male reproductive system is both internal and external.

The testes are located within the scrotal sac, the pouch of skin located below the man's penis. These are the two organs that produce both sperm and testosterone, the male hormone that helps maintain the male sexual characteristics. As sperm are produced, they pass from the testes through the coiled channels of the epididymis, an organ that stores and nourishes them as they mature.

Once sperm are completely mature, they move into the vas deferens. This tubal structure connects the epididymis with the seminal vesicles, the two pouchlike glands that provide storage for the mature sperm. The entire process of sperm formation to maturation takes about 72 days.

When a man ejaculates (or expels the fluid from his penis) during intercourse, sperm from the seminal vesicles combine with a thick fluid from the prostate gland to create semen. This fluid (or ejaculate) is deposited into the woman's vagina.

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Sperm Development

The development of normal, mature sperm is key in establishing male fertility and involves an interplay of several factors:

• An exchange of hormonal messages between the brain and the testicles
• A secretion of necessary reproductive hormones (testosterone) by Leydig cells and normal sperm development within Sertoli cells
• Normal transport of developing sperm from testicles to epididymis to vas deferens

The production of sperm is primarily regulated by three hormones:

• FSH
• LH
• Testosterone

In the male, pituitary hormones are responsible for maintaining the sperm production process. The pituitary gland, which is located at the base of the brain, secretes FSH and LH, the same hormones necessary for regulating the female's reproductive functions. FSH is responsible for stimulating sperm production in the testicles. LH stimulates the production of testosterone. Under the influence of Sertoli cells and specific hormones, immature sperm cells develop through several stages and eventually become mature sperm cells, called spermatozoa. Spermatozoa are not yet motile. They must pass through the epididymis, where after 18–24 hours, they gain motility (movement). After acquiring the ability to move, mature sperm are stored in the vas deferens until ejaculation.

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