testosterone

Testosterone is a steroid hormone from the androgen group. Testosterone is made in the testicles of men and in the ovaries of women. It is the primary male sex hormone. In both males and females, it plays key roles in health and well-being. Examples include enhanced libido, energy, immune function, and protection against osteoporosis.

Effects of testosterone on people

In general, androgens promote protein synthesis and growth of those tissues with androgen receptors. Testosterone effects can be classified as virilizing and anabolic effects, although the distinction is somewhat artificial, as many of the effects can be considered both. Anabolic effects include growth of muscle mass and strength, increased bone density and strength, and stimulation of height growth and bone maturation. Virilizing effects include maturation of the sex organs, particularly the penis the formation of the scrotum in fetuses, and after birth (usually at puberty) a deepening of the voice, growth of the beard and torso hair. Many of these fall into the category of male secondary sex characteristics. Increased testosterone causes deepening of the voice in both sexes at puberty. To take advantage of its virilizing effects, testosterone is often administered to transmen (female-to-male transsexual people) as part of the hormone replacement therapy, with a "target level" of the normal male testosterone level. And like-wise, male-to-female transsexuals are prescribed anti-androgens to decrease the level of testosterone in the body and allow for the effects of estrogen to develop.

Testosterone effects can also be classified by the age of usual occurrence. For postnatal effects in both males and females, these are mostly dependent on the levels and duration of circulating free testosterone.

Most of the prenatal androgen effects occur between 7 and 12 weeks of gestation.

• Genital virilization (midline fusion, phallic urethra, scrotal thinning and rugation, phallic enlargement)
• Development of prostate and seminal vesicles

Early infancy androgen effects are the least understood. In the first weeks of life for male infants, testosterone levels rise. The levels remain in a pubertal range for a few months, but usually reach the barely detectable levels of childhood by 4-6 months of age. The function of this rise in people is unknown. It has been speculated that "brain masculinization" is occurring since no significant changes have been identified in other parts of the body.

Early postnatal effects are the first visible effects of rising androgen levels in childhood, and occur in both boys and girls in puberty.

• Adult-type body odor
• Increased oiliness of skin and hair, acne
• Pubarche (appearance of pubic hair)
• Axillary hair
• Growth spurt, accelerated bone maturation
• Fine upper lip and sideburn hair

Advanced postnatal effects begin to occur when androgen has been higher than normal adult female levels for months or years. In males these are normal late pubertal effects, and only occur in women after prolonged periods of excessive levels of free testosterone in the blood.

• Phallic enlargement (including clitoromegaly)
• Increased libido and erection frequency
• Pubic hair extends to thighs and up toward umbilicus
• Facial hair (sideburns, beard, mustache)
• Chest hair, periareolar hair, perianal hair
• Increased muscle strength and mass
• Deepening of voice
• Growth of spermatogenic tissue in testes, male fertility
• Growth of jaw and remodelling of facial bone contours
• Completion of bone maturation and termination of growth (via estradiol metabolites)

"Adult testosterone effects" are important in adult males, and may decline as testosterone levels decline in the later decades of adult life.

• Maintenance of muscle mass and strength
• Maintenance of bone density and strength
• Libido and erection frequency
• Mental and physical energy

This article is based on a GNU FDL LGBT Wikia article: Testosterone

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