Testosterone is the primary male sex hormone and androgen in males. It is associated with increased aggression , sex drive , dominance , courtship display , and a wide range of behavioral characteristics. Excessive levels of testosterone in men may be associated with hyperandrogenism , higher risk of heart failure , increased mortality in men with prostate cancer , [ 7 ] and male pattern baldness. Testosterone is a steroid hormone from the androstane class containing a ketone and a hydroxyl group at positions three and seventeen respectively.
It is biosynthesized in several steps from cholesterol and is converted in the liver to inactive metabolites. On average, in adult males, levels of testosterone are about seven to eight times as great as in adult females. In addition to its role as a natural hormone, testosterone is used as a medication to treat hypogonadism and breast cancer. It is also used illicitly to enhance physique and performance , for instance in athletes. In general, androgens such as testosterone promote protein synthesis and thus growth of tissues with androgen receptors.
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.
Effects before birth are divided into two categories, classified in relation to the stages of development. The first period occurs between 4 and 6 weeks of the gestation. Examples include genital virilisation such as midline fusion, phallic urethra , scrotal thinning and rugation , and phallic enlargement; although the role of testosterone is far smaller than that of dihydrotestosterone.
There is also development of the prostate gland and seminal vesicles. During the second trimester, androgen level is associated with sex formation. Prenatal androgens apparently influence interests and engagement in gendered activities and have moderate effects on spatial abilities.
