Sexual Maturation in Girls

In most girls, the initial indication of puberty is the appearance of breast buds, an event known as thelarche, which occurs between 8 and 13 years of age (Fig. 16-1). This is followed in approximately 2 to 6 months by growth of pubic hair on the mons pubis, known as adrenarche (Fig. 16-2). In a minority of normally developing girls, however, pubic hair may precede breast development. The average age of thelarche for white girls is 10 years, with a range of 8 to 12.75 years; for African-American girls, the average age of thelarche is earlier, around 9 years, with a range of 7 to 11 years (Herman-Giddens, 2006). The average age of thelarche for Hispanic girls falls somewhere between the other two groups.

The initial appearance of menstruation, or menarche, occurs about 2 years after the appearance of the first pubescent changes, approximately 9 months after attainment of peak height velocity, and 3 months after attainment of peak weight velocity. There is evidence that girls are developing secondary sex characteristics at a younger age with differences between white and African-American girls. The explanation for this is not yet clear but appears to be influenced by being overweight as well as environmental influences. The normal age range of menarche is usually to 15 years, with the average age being 12 years, 4 months for North American girls (Wu, Mendola, and Buck, 2002). Ovulation and regular menstrual periods usually occur 6 to 14 months after menarche. Girls may be considered to have pubertal delay if breast development has not occurred by age 13 years or if menarche has not occurred within 4 years of the onset of breast development.

Sexual Maturation in Boys

The first pubescent changes in boys are testicular enlargement accompanied by thinning, reddening, and increased looseness of the scrotum (Fig. 16-3). These events usually occur between and 14 years of age. Early puberty is also characterized by the initial appearance of pubic hair. Penile enlargement begins, and testicular enlargement and pubic hair growth continue throughout midpuberty. During this period, there is also increasing muscularity, early voice changes, and development of early facial hair. Temporary breast enlargement and tenderness, gynecomastia, are common during midpuberty, occurring in up to one third of boys. The spurts in height and weight occur concurrently toward the end of midpuberty. For most boys, breast enlargement disappears within 2 years. By late puberty, there is a definite increase in the length and width of the penis, testicular enlargement continues, and first ejaculation occurs. Axillary hair develops, and facial hair extends to cover the anterior neck. Final voice changes occur secondary to the growth of the larynx. Concerns about pubertal delay should be considered for boys who exhibit no enlargement of the testes or scrotal changes by to 14 years of age or if genital growth is not complete 4 years after the testicles begin to enlarge.

Sex Differences in General Growth Patterns

Sex differences in general growth and distribution patterns are apparent in skeletal growth, muscle mass, adipose tissue, and skin. Skeletal growth differences between boys and girls are apparently a function of hormonal effects at puberty and are evident primarily in limb length. The earlier cessation of growth in girls is caused by epiphyseal unity under the potent effect of estrogen secretion, and the hormonal effect on female bone growth is much stronger than the similar effect of testosterone in boys. In boys, the prolonged growth period before puberty and the less rapid epiphyseal closure are reflected in their greater overall height and longer arms and legs. Other skeletal differences are increased shoulder width in boys and broader hip development in girls.

Hypertrophy of the laryngeal mucosa and enlargement of the larynx and vocal cords occur in both boys and girls to produce voice changes. Girls’ voices become slightly deeper and considerably fuller, but the effect in boys is striking. The change in the voice of adolescent boys occurs between Tanner stages 3 and 4, with the voice often shifting uncontrollably from deep to high tones in the middle of a sentence. The average lengthening of the vocal cords is 10.9 mm (0.4 inch) for boys and 4.2 mm (0.17 inch) for girls.

Growth of lean body mass, principally muscle, which tends to occur after the bone growth spurt, takes place steadily during adolescence. Lean body mass is both quantitatively and qualitatively greater in boys than in girls at comparable stages of pubertal development. Muscle development, under the influence of androgenic hormones, increases steadily. Muscles become remarkably well developed in boys, but in girls, muscle mass increase is proportionate to general tissue growth.

Nonlean body mass, primarily fat, is also increased but follows a less orderly pattern. There may be a transient increase in subcutaneous fat just before the skeletal growth spurt, especially in boys. This is followed 1 to 2 years later by a modest to marked decrease, which is again more marked in boys. Later, variable amounts of fat are deposited to fill out and contour the mature physique in patterns characteristic of the adolescent’s sex, particularly in the regions over the thighs, hips, and buttocks and around the breast tissue. It should be noted, however, that pediatric obesity is steadily on the increase in the United States, and obesity can change the timing and sequence of puberty. Girls with thelarche as the first sign of puberty have earlier menarche and greater body fat and body mass index (BMI) at menarche than girls with adrenarche as the first pubertal sign. This may have long-term effects for increased risk of adult adiposity and obesity (Biro, Lucky, Simbarti, and others, 2003). Kaplowitz (2008) states that evidence indicates a causal relationship between obesity and onset of early puberty in girls rather than earlier puberty causing an increase in body fat; no correlations between body fat and earlier puberty in boys have been reported.

Hormonal influences during puberty cause acceleration in growth and maturation of the skin and its structural appendages. Sebaceous glands become extremely active at this time, especially those on the genitalia and in the “flush areas” of the body (i.e., face, neck, shoulders, upper back, and chest). This increased activity and the structural nature of the glands are extremely important in the pathogenesis of a common problem of puberty: acne (see Chapter 30). The eccrine sweat glands, present almost everywhere on the human skin, become fully functional and respond to emotional as well as thermal stimulation. Heavy sweating appears to be more pronounced in boys than in girls. The apocrine sweat glands, nonfunctional in childhood, reach secretory capacity during puberty. Unlike the eccrine sweat glands, the apocrine glands are limited in distribution and grow in conjunction with hair follicles in the axillae, around the areola of the breast, around the umbilicus, on the external auditory canal, and in the genital and anal regions. Apocrine glands secrete a thick substance as a result of emotional stimulation that, when acted on by surface bacteria, becomes highly odoriferous.

Body hair assumes characteristic distribution patterns and changes texture during puberty. Under the influence of gonadal and adrenal androgens, hair coarsens, darkens, and lengthens at sites related to secondary sex characteristics. Pubic and axillary hair appears in both sexes, although pubic hair is more extensive in males than in females. Beard, mustache, and body hair on the chest, upward along the linea alba, and sometimes on other areas (e.g., back and shoulders) appears in males and is androgen dependent. Extremity hair appears in varying amounts in both males and females but is also more prolific in males.

Peer Group

Adolescents are usually social, gregarious, and group minded. Thus, the peer group has an intense influence on adolescents’ self-evaluation and behavior. To gain acceptance by a group, younger teenagers tend to conform completely in such things as mode of dress, hairstyle, taste in music, and vocabulary. Teenagers use the peer group as a yardstick of what is normal.

The school is psychologically important to adolescents as a focus of social life. Teenagers usually distribute themselves into a relatively predictable social hierarchy. They know to which groups they and others belong. A sense of school connectedness and optimal social connectedness is associated with positive outcomes for school completion, positive mood, and decreased high-risk behavior in adolescents (Bond, Butler, Thomas, and others, 2007). School connectedness is correlated with caring teachers and the absence of prejudice or discrimination from peers. A sense of school connectedness is less dependent on class size, attendance, academic preparation, and parental involvement (Maes and Lievens, 2003).

Within the larger groups are smaller, distinct, and exclusive crowds or cliques of selected close friends who are emotionally attached to one another. The selection is based on common tastes, interests, and background. Although cliques may become formalized, most remain informal and small. However, each has an identifying feature that proclaims its difference from others and its solidarity within itself in much the same manner as the adolescent generation as a whole sets itself apart from the adult generation. Cliques are usually made up of one sex, and girls tend to be more cliquish than boys and to have a greater need for close friendships (Fig. 16-4). Within the intimacy of the group, adolescents gain support in learning about themselves, consideration for the feelings of others, and increased ego development and self-reliance.