Puberty is an endocrine process that involves the physical, P emotional, and sexual transition from childhood to adult-hood. It occurs gradually in a series of well-definedevents and milestones. When puberty is early or delayed, an understanding of the hormonal events of puberty and the sequence of physical changes is essential to diagnosis of a potential problem. Knowledge of the events of puberty is also key to understanding the process of reproduction.
NORMAL PUBERTAL DEVELOPMENT
A series of endocrine events initiate the onset of secondary sexual maturation. The hypothalamic–pituitary–gonadal axis begins to function during fetal life and remains active during the first few weeks following birth, after which time the axis becomes quiescent secondary to enhanced negative feedback of estrogen. The hypothalamic–pituitary–gonadal axis again becomes active during puberty, triggering the production of gonadotropin-releasing hormone (GnRH). The gonadotropins control production of sex steroids from the ovary, and higher levels cause the physical changes of puberty. At approximately 6 to 8 years of age, adrenarche, the increase in production of androgens, occurs in the adrenal glands. Adrenarche involves the increased pro-duction of dehydroepiandrosterone (DHEA), which can be converted to more potent androgens (testosterone and dihydrotestosterone).
The process of secondary sexual maturation requires ap-proximately 4 years. It takes place in an orderly, predictablesequence that includes growth acceleration, breast devel-opment (thelarche), pubic hair development (pubarche) [maximum growth rate], menarche, and ovulation. The ini-tial event is accelerated growth; however, this may be sub-tle, and breast budding is easier to detect as the first event. The sequence of breast development and pubic hair growth is referred to as Tanner’s classification of sexual maturity (Fig. 34.1).
The ages at which some of these events occur are pre-sented in Table 34.1. There is a strong relationship be-tween body fat content and the onset of puberty. Mild to moderate obesity results in earlier puberty, whereas thin-ness results in later puberty. The onset of puberty is also marked by significant ethnic differences. Puberty usually begins earlier in African-American and Mexican-American girls than in white girls, and much of this difference may result from differences in body mass index (see Table 34.1). In contrast, puberty tends to begin in Asian-American girls later than in white girls. Body mass index may account for most of this difference, although as yet undefined genetic or environmental factors may also be important.