Testosterone
Testosterone is a hormone found in the human body. It is secreted from the interstitial tissue of the testes in males, from the theca cells of the ovaries in females, and from the zona reticularis of the adrenal cortex in both sexes. Testosterone is classified as an androgen sex steroid hormone.
Secretion and Production
Insulin is produced in and secreted from the interstitial tissue of the testes in males, the theca cells of the ovaries in females, and the adrenal glands in both sexes. However, in females, it’s secreted in much smaller amounts than in males. It is derived from cholesterol.
General effects of testosterone secretion in both sexes are promotion of protein synthesis, promotion of growth in tissues with androgen receptors, growth of muscle mass and strength, increased bone density and strength, and stimulation of linear growth and bone maturization. Additionally, in both sexes, testosterone plays a key role in health and well-being by enhancing libido, energy, and immune function, and by protecting against osteoporosis.
More specific effects can be classified by age. Prenatal testosterone effects occur between 7 and 12 weeks of gestation. They are genital virilization and the development of prostate and seminal vesicles. In early pubescent children of both sexes, testosterone secretion causes adult-type body odor, increased oiliness of the skin and hair, appearance of pubic hair, growth, accelerated bone maturization, and, in males, fine upper lip and sideburn hair.
In late pubescent males, testosterone causes phallic enlargement, increased libido and erection frequency, increased growth of pubic hair, growth of facial, chest, periareolar, and perianal hair, increased aggressiveness, decrease in fat, increased muscle mass and strength, deepening of voice, growth of the Adam’s apple, fertility and growth of spermatogenic tissue in testes, growth of jaw, brow, chin, and nose, widening of shoulders, expansion of rib cage, and the completion of bone maturization and growth.
After puberty and through adulthood, the effects of testosterone in both males and females are to maintain muscle mass and strength, maintain bone density and strength, provide mental and physical energy, and, in males, provide libido and erection frequency.
Pharmacological Uses
Synthetic testosterone is available in many forms, including injectable, oral, buccal, transdermal skin patches, and transdermal creams or gels. Primarily, synthetic testosterone is used to treat males with testosterone deficiency. However, it is also commonly used medically to treat infertility, lack of libido, erectile dysfunction, osteoporosis, and anemia. Additionally, it is often prescribed to promote growth, penile enlargement, and appetite stimulation.
One recent common form of use of synthetic testosterone is as a drug for female-to-male transsexuals. In women, if amounts of testosterone in the body are equal to those of men, then it has the same effects as those that occur in pubescent boys. Therefore, it is commonly prescribed to these transsexuals to promote male characteristics.
Non-medically, synthetic testosterone is commonly used as a physical and performance enhancing drug by athletes. Testosterone, an anabolic steroid, enhances muscle development, strength, and endurance. However, its use is illegal in most sports.