Testosterone << tehs TAHS tuh rohn >> is a hormone that stimulates sexual development in male human beings. It belongs to a family of hormones called androgens. Androgens are produced primarily by the testicles, a pair of male sex glands (see Testicle). The ovaries in females and the adrenal glands in both sexes also yield small amounts of testosterone and other androgens.
During a boy’s early teen-age years, his testicles are stimulated by a hormone from the pituitary gland to secrete increasing amounts of testosterone, particularly during sleep. Testosterone enters the blood and acts on certain tissues in the body to cause various physical changes. These changes include growth of hair on the face and in the genital area, muscle development, deepening of the voice, and maturation of the sex organs. Testosterone also helps in the production of sperm by the testicles. After a man reaches old age, the testicles produce smaller amounts of testosterone. In adult females, testosterone contributes to the formation of estrogens by the ovaries. Estrogens are hormones necessary for female sexual development. See Estrogen.
In many kinds of animals, testosterone influences male sexual behavior. For example, some deer breed in the fall. At this time, the testicles of male deer secrete large amounts of testosterone. As a result, the males spend much time pursuing females.
Drugs called anabolic steroids are made from testosterone. They are used by some athletes who feel such drugs increase strength and endurance. Most doctors agree that anabolic steroids can have dangerous side effects and should not be used. See Steroid (The sex steroids).
