Adelina M. Emmi and Lawrence C. Layman Normal Puberty Physiology
Normal puberty is a progression of events in both girls and boys that is generally complete in 3-4 years. In females, thelarche (breast buds) is usually the first sign of estrogen production and occurs at an average age of 10.5 years, while pubarche (pubic hair growth) generally occurs about 6 months later. In 10-20% of girls, pubarche is the first event. These are estimates; thelarche varies slightly among different racial groups (white: 10.4 years; black: 9.5 years; Mexican/American: 9.8 years). Tanner Stages are used to classify the stages of puberty in both boys and girls (Table 2.1). Tanner Stage 1 is prepubertal, while Stage 5 is the fully mature adult status. Peak growth rate for girls generally is seen at Tanner Stage 3 breast development.
Adrenarche is the result of adrenal androgen production (androstenedione, DHEA, and particularly DHEAS), which begins prior to changes in gonadotropin secretion at 6-8 years of age and continues through the mid-teens. During female puberty, growth in height occurs at a rate of 4-5 cm/year in early puberty. As estrogen production increases, growth hormone increases, resulting in increased IGF-1 and IGFBP-3, which mediates skeletal growth. Maximal growth velocity occurs in girls at age 12 and usually results in about a 9 cm increase in height. Menarche (initiation of menses) occurs on the downward arm of the growth curve at a median age of 12.5 years (white: 12.6 years; black: 12.15 years; Mexican/ American: 12.3 years). A variety of additional factors affect pubertal onset, such as weight, stress, and extreme physical activity. Some authors have noted a younger age of onset of breast development and possibly menarche in African-American girls that may be attributable to a greater BMI.
In boys the initial pubertal event is testicular growth, which begins at about 10.5 years of age. When the testes exceed 2.5 cm in any dimension, the onset of puberty is approaching. Pubarche frequently starts simultaneously with testicular development. Axillary hair growth occurs at about the time of peak height velocity (about age 14 years in boys and 12 in girls) (Table 2.2).
The GnRH pulse generator is the principal regulator of puberty through its control of pituitary gonadotropins and is active early in life. As a result, gona-dotropin levels change throughout fetal development, childhood, puberty and adulthood. Gonadotropins begin to rise at 10 weeks gestation, peak at
Table 2.1. Tanner staging in females with approximate ages in parentheses
Stage 1 (prepubertal) Stage 2
Stage 4 Stage 5
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