Testosterone causes males to develop anatomical and a physiological male sexual characteristics. Testosterone, which is categorized as an androgen, or male hormone, is secreted by the testes in relatively constant concentrations throughout a man's adult life. It produces and maintains characteristically male qualities and behaviors, affecting both the physical body and the brain.
Reproductive System
The effects of testosterone on a male start very early in life. In her book "Human Physiology," Dr. Lauralee Sherwood explains that early embryos look physically identical, regardless of the gender determined by their genetics. At around 6 to 7 weeks gestational age, male embryos start producing the hormone testosterone, which leads to the first physical differences between males and females. While early embryos have two sets of primitive reproductive ducts, testosterone causes the female set to atrophy, while the male set proliferates. The hormone also causes undifferentiated tissue to develop into the male external genitals--the penis and scrotum.
Puberty
Additional key differences between men and women arise as boys enter puberty and the testes begin secreting testosterone once more. According to Dr. Gary Thibodeau in his book, "Anatomy and Physiology," testosterone causes a male's body to thicken through the skeletal and muscular systems. His voice deepens relative to that of a young boy or of a woman as testosterone thickens the tissue of the larynx, or voice box. His testes begin producing sperm, and he becomes capable of reproduction. He develops a stronger body odor, oilier skin, and more acne than a boy, also as a result of the hormone.
Psychological Effects
Testosterone doesn't just affect a man's physical body--it also affects his brain. In their book, "You: Having A Baby," Drs. Michael Roizen and Mehmet Oz explain that early testosterone secretion in an embryo changes the brain structure relative to that of a female. The changes predispose the male toward increased sexual drive and aggression and toward less prolific communication skills. At puberty, increased testosterone levels exacerbate these changes, leading to male sexual drive and increased aggression. Unlike female hormones, testosterone concentrations in men are relatively constant throughout adult life, meaning that behavior and emotions don't cycle regularly--like those of females--in healthy men.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
- "You: Having A Baby"; Michael Roizen, M.D. and Mehmet Oz, M.D.; 2009
