genitourinary disorders
Male Reproductive Endocrinology
Sexual Differentiation, Adrenarche, and Puberty
In the embryo, the presence of a Y chromosome triggers development and growth of the testes, which begin secretingtestosteroneand a müllerian duct inhibitor by about 7 weeks of gestation.Testosteronevirilizes the wolffian duct (which develops into the epididymis, vas deferens, and seminal vesicles). Dihydrotestosterone promotes development of the male external genitals.Testosteronelevels peak in the 2nd trimester and fall to almost zero by birth.Testosteroneproduction rises briefly during the first 6 months of life, after whichtestosteronelevels remain low until puberty. Müllerian inhibitory factor causes regression of the female genital organs in the fetus. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are elevated at birth but fall to low levels within a few months, remaining low or undetectable throughout the prepubertal years. Through an unknown mechanism, blood levels of the adrenal androgens dehydroepiandrosterone (DHEA) and DHEA sulfate begin to increase several years before puberty. Their conversion totestosteronein small amounts initiates pubic and axillary hair growth (adrenarche). Adrenarche can occur as early as 9 or 10 years of age. The mechanisms that initiate puberty are unclear, although early in puberty the hypothalamus becomes less sensitive to the inhibitory effects of sex hormones. This desensitization increases secretion of LH and FSH, corresponding to pulsatile gonadotropin-releasing hormone (GnRH) secretion, and stimulatingtestosteroneand sperm production. In boys, the increasedtestosteronelevels cause pubertal changes, the first of which is growth of the testes and scrotum. Later, penile length, muscle mass, and bone density increase; the voice deepens; and pubic and axillary hair becomes denser and thicker (see figure). Bars indicate normal ranges. No mean is available for change in habitus. 