Testosterone is a hormone produced by both men and women, though it's made in much higher concentrations in men. It's responsible for many adult male characteristics, both physical and psychological, and allows for reproduction. The hormone plays an especially critical role at two times in life, prenatally and at puberty, from which point it is secreted through the rest of adulthood.
Function
A primary function of testosterone is to produce male characteristics. While prepubescent boys and girls appear, act, and sound very similar--with the obvious exception of their external genitalia--adult males and females are easily distinguished from one another by voice, size, weight, and even their patterns of thought and behavior.
Prenatal Effects
The first effects of testosterone are prenatal. Very early in human development, all fetuses--regardless of whether they're chromosomally male or female--have identical internal and external body parts. In the presence of testosterone, male internal parts develop, while female internal parts regress. Identical proto-genital tissue differentiates into male organs, including the penis and scrotum, under the influence of testosterone.
Puberty Effects
Once a boy enters puberty, his brain signals his testes to begin making testosterone, which leads to a variety of body changes. It takes testosterone to maintain these changes, so his body continues to produce the hormone throughout life to maintain his "maleness." In his book "Anatomy and Physiology," Dr. Gary Thibodeau explains that testosterone causes the genitals to enlarge, the testes to begin making sperm, the body to grow thicker hair, and the larynx to grow and thicken.
Misconceptions
While testosterone is technically an androgen, or male hormone, it's not produced only in males. In fact, females also make small amounts of the hormone. In women, the hormone acts to increase sexual desire and interest in reproduction. Women with a lack of testosterone may have diminished sex drive compared to those who produce it in more normal amounts. High levels of testosterone in women deepen the voice, can lead to acne, cause muscles to thicken, and may lead to development of body hair.
Expert Insight
Some individuals seek to amplify the "desirable" effects of testosterone by supplementing with anabolic steroids. An anabolic steroid increases synthesis of muscle, and mimics testosterone in some of its effects. Unfortunately, steroid use doesn't simply result in enhanced musculature. Men who use steroids may have more acne, mood imbalances, and shrunken genitals. Their sperm counts may also fall, since the presence of these testosterone-like substances signal the brain to reduce production of testosterone, which can actually lead to diminished reproductive capacity.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "You: Having A Baby"; Michael Roizen, M.D. and Mehmet Oz, M.D.; 2009
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
