Biologic Development

Adolescence is defined as a period of development; puberty is the biologic process in which a child becomes an adult. These changes include appearance of the secondary sexual characteristics, increase to adult size, and development of reproductive capacity. Adrenal production of androgen (chiefly dehydroepiandrosterone sulfate [DHEAS]) may occur as early as 6 yr of age, with development of underarm odor and faint genital hair (adrenarche). Levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) rise progressively throughout middle childhood without dramatic effect. Rapid pubertal changes begin with increased sensitivity of the pituitary to gonadotropin-releasing hormone (GnRH); pulsatile release of GnRH, LH, and FSH during sleep; and corresponding increases in gonadal androgens and estrogens. The triggers for these changes are incompletely understood, but may involve ongoing neuronal development throughout middle childhood and adolescence.

Data regarding the timing for the onset of puberty in girls are controversial (Table 104-2). Several studies from 1948 to 1981 identified the average age for the onset of breast development to range from 10.6-11.2 yr of age. Multiple reports since 1997 suggest a significantly earlier onset of breast development, ranging from 8.9-9.5 yr in African-American girls and 10.0-10.4 yr in white girls. There also appears to be a small secular trend toward decreasing ages for the onset of pubic hair development and menarche. The reasons for the larger decrease in age for breast development may include the epidemic of childhood obesity as well as exposure to estrogen-like toxins in the environment that include certain pesticides, plastics, phytoestrogens, and industrial compounds along with beef fattened with subcutaneous estrogen pellets.

It is less clear whether there is also a secular trend for decreasing age for onset of puberty in boys (Table 104-3). It appears that, over the past 40 yr, the average age for the onset of genital and pubic hair development may have decreased by about a year. The onset of puberty in African-American boys precedes that in white boys by at least 6 mo.

Once the onset of puberty has begun, the resulting sequence of somatic and physiologic changes gives rise to the sexual maturity rating (SMR), or Tanner stages. Figures 104-1 and 104-2 depict the somatic changes used in the SMR scale; Tables 104-4 and 104-5 also describe these changes. Figures 104-3 and 104-4 depict the typical sequence of pubertal changes in boys and girls, respectively. The range of normal progress through sexual maturation is wide.

Figure 104-1 Sexual maturity ratings (2 to 5) of pubic hair changes in adolescent boys (A) and girls (B) (see Tables 104-4 and 104-5).

(Courtesy of J.M. Tanner, MD, Institute of Child Health, Department for Growth and Development, University of London, London, England.)

Figure 104-2 Sexual maturity ratings (1 to 5) of breast changes in adolescent girls.

(Courtesy of J.M. Tanner, MD, Institute of Child Health, Department for Growth and Development, University of London, London, England.)

Table 104-4 CLASSIFICATION OF SEXUAL MATURITY STATES IN GIRLS

SMR, sexual maturity rating.

From Tanner JM: Growth at adolescence, ed 2, Oxford, England, 1962, Blackwell Scientific.

Figure 104-3 Sequence of pubertal events in males. PHV, peak height velocity.

(From Root AW: Endocrinology of puberty, J Pediatr 83:1, 1973.)

Figure 104-4 Sequence of pubertal events in females. PHV, peak height velocity.

(From Root AW: Endocrinology of puberty, J Pediatr 83:1, 1973.)

In girls, the 1st visible sign of puberty and the hallmark of SMR2 is the appearance of breast buds, between 8 and 12 yr of age. Menses typically begins 2- yr later, during SMR3-4 (median age, 12 yr; normal range, 9-16 yr) (see Fig. 104-4). Less obvious changes include enlargement of the ovaries, uterus, labia, and clitoris, and thickening of the endometrium and vaginal mucosa.

In boys, the 1st visible sign of puberty and the hallmark of SMR2 is testicular enlargement, beginning as early as  yr. This is followed by penile growth during SMR3. Peak growth occurs when testis volumes reach approximately 9-10 cm³ during SMR4. Under the influence of LH and testosterone, the seminiferous tubules, epididymis, seminal vesicles, and prostate enlarge. The left testis normally is lower than the right. Some degree of breast hypertrophy, typically bilateral, occurs in 40-65% of boys during SMR2-3 due to a relative excess of estrogenic stimulation.

Growth acceleration begins in early adolescence for both sexes, but peak growth velocities are not reached until SMR3-4. Boys typically peak 2-3 yr later than girls, begin this growth at a later SMR stage (Fig. 104-5), and continue their linear growth for approximately 2-3 yr after girls have stopped. The asymmetric growth spurt begins distally, with enlargement of the hands and feet, followed by the arms and legs, and finally, the trunk and chest, giving young adolescents a gawky appearance. Rapid enlargement of the larynx, pharynx, and lungs leads to changes in vocal quality, typically preceded by vocal instability (voice cracking). Elongation of the optic globe often results in nearsightedness. Dental changes include jaw growth, loss of the final deciduous teeth, and eruption of the permanent cuspids, premolars, and finally, molars (Chapter 299). Orthodontic appliances may be needed, secondary to growth exacerbations of bite disturbances.

Figure 104-5 Height velocity curves for American boys (solid line) and girls (dashed line) who have their peak height velocity at the average age (i.e., average growth tempo).

(From Tanner JM, Davies PSW: Clinical longitudinal standards for height and height velocity for North American children, J Pediatr 107:317, 1985.)

Cognitive and Moral Development (See Also Chapter 6)

While adolescence has traditionally been described as the time of transition from concrete operational thinking to formal logical thinking (abstract thought), other processes include the important but distinct contributions of reasoning (cognitive abilities) and judgment (the process of thinking through the consequences of alternative decisions or actions). Because these processes may develop at very different rates, young adolescents may be able to apply formal logical thinking to schoolwork, but not to personal dilemmas. When emotional stakes are high, adolescents may regress to more concrete operational and/or magical thinking. This can interfere with higher-order cognition and ultimately affect the ability to perceive long-term outcomes of current decision-making. The development of moral thinking roughly but imperfectly parallels cognitive development. Whereas younger children view relationships with adults in terms of power and fear of punishment, preadolescents begin to perceive right and wrong as absolute and unquestionable. During mid-adolescence most adolescents become more multidimensional in their thinking and are better able to contemplate hypothetical situations and the relationship between varied actions or decisions and differing outcomes. Despite their increasing abilities for complex decision-making, adolescent decision-making remains particularly susceptible to emotions.

Neuroimaging has enabled greater insight into changes in developing brains that help explain variations in decision-making capacities. Some theorists argue that the transition from concrete to formal operations follows from quantitative increases in knowledge, experience, and cognitive efficiency rather than from a qualitative reorganization of thinking. Consistent with this view is a steady rise in cognitive processing speed from late childhood through early adulthood, associated with a reduction in synaptic number (pruning of less-used pathways) and continued myelination of neurons. Adolescents also experience the development of the dorsolateral prefrontal cortex and the superior temporal gyrus, areas responsible for higher-order associations, including the ability to inhibit impulses, weigh the consequences of decisions, prioritize, and strategize. It is unclear whether the hormonal changes of puberty directly affect cognitive development. Related to neurobehavioral maturation, adolescents may experience an increased intensity of emotion and/or greater inclination to seek experiences that create such high-intensity emotions. Cognitive development also differs by gender, with girls developing at earlier ages than boys.

Self-Concept

Self-consciousness increases exponentially in response to the somatic transformations of puberty. Self-awareness at this age centers on external characteristics, in contrast to the introspection of later adolescence. It is normal for early adolescents to be preoccupied with their body changes, scrutinize their appearance, and feel that everyone else is staring at them (Elkind’s imaginary audience).

The media, with its overrepresentation of sex, violence, and substance use, has a profound influence on cultural norms and an adolescents’ sense of identity. Adolescents use, on average, 7 hr of media per day (e.g., television, Internet). Over half of all high school students have a television in their bedrooms, 70% live in homes with a personal computer, and the proportion with Internet access is approximately 75%. The advent (and ubiquity) of cell phones with texting capability and social networking sites have greatly enhanced communication among adolescents of all ages.

This exposure may cause girls to develop a distorted sense of femininity, and they may be at risk for viewing themselves as overweight, leading to eating disorders and depression (Chapter 26). Similarly, boys may have difficulties with self-image. Images of masculinity may be confusing, leading to self-doubt, insecurity, and misleading conceptions about male behavior. Adolescents who develop earlier than their peers, especially girls, may have higher rates of school difficulty, body dissatisfaction, and depression. These adolescents look like adults and may have adult expectations placed on them, but are not cognitively or psychologically mature.

Relationships with Family, Peers, and Society

In early adolescence, young teens become less interested in parental activities and more interested in the peer group, typically with peers of the same sex. Early adolescents often disregard parents’ advice about safety, appearance, etiquette, and overall comportment and display markedly different values, tastes, and interests. Superficial differences may spark conflicts that are truly about power or difficulty accepting separation. Other core individual characteristics, like sexual identity, might become a source of conflict with potentially damaging and long-lasting consequences for the entire family. Adolescents also seek more privacy, which may contribute to family discord.

The trend toward separation from family often involves selecting adults outside of the family as role models and developing close relationships with particular teachers or the parents of other children. Organizations such as scouting or sports teams can also provide an important sense of extrafamilial belonging.

Early adolescents often socialize in same-sex peer groups. Deepening relationships with peers contributes importantly to their gradual individuation and independence from families of origin. Indicative of increasing sexual awareness, teasing directed against the other gender, homophobic comments and acts, and sexually-related gossip are common, albeit inappropriate, means to cope with personal insecurities and seek social approval. Belonging is all important. In one-to-one friendships, boys and girls differ in important ways. Female friendships may center on emotional intimacy, whereas male relationships may focus more on activities.

An early adolescent’s relationship to society centers on school. The shift from elementary school to middle school or junior high school entails giving up the protection of a single classroom in exchange for the additional stimulation and responsibility involved in moving from class to class. This change in school structure mirrors and reinforces the changes involved in separating from the family.

Sexuality

Anxiety and interest in sex and sexual anatomy increase during early puberty. It is normal for young adolescents to compare themselves with others. In boys, ejaculation occurs for the 1st time, usually during masturbation and later as nocturnal emissions, and may be a cause of anxiety. Early adolescents sometimes masturbate together; isolated incidents of mutual sexual exploration are not necessarily a sign of homosexuality. The prevalence of other forms of sexual behavior, other than masturbation, varies by culture but generally are less common in early adolescents.

Implications for Pediatricians and Parents

Parents may have concerns that they are hesitant to discuss. Parents can be interviewed separately from the adolescent to avoid undermining the adolescent’s trust. When interviewing and examining an adolescent, health care providers should keep in mind that physical maturation correlates with sexual maturity, whereas psychosocial development correlates more closely with chronological age. Early adolescents typically need reassurance that the somatic changes they are experiencing are common and normal.

The pediatrician needs to help parents differentiate between the normal discomforts of the age and truly concerning behaviors. Bids for autonomy, such as avoiding family activities, demanding privacy, and increasing argumentativeness, are normal; extreme withdrawal or antagonism may be dysfunctional. Bewilderment and dysphoria at the start of junior high school are normal; continued failure to adapt several weeks to months later suggests a more serious problem. Risk-taking is limited in early adolescence; escalation of risk-taking behaviors is problematic. Parents must adapt discipline measures to the changing abilities of the adolescent, who can think through problems, assess consequences, and problem solve. Thus, the development of negotiation strategies is critical. Children and adolescents raised by parents who use negotiating as part of child rearing have more positive outcomes than those raised by parents who use more authoritarian or permissive styles.

Biologic Development

Growth accelerates above the prepubertal rate of 6-7 cm (3 in) per year during middle adolescence. In the average girl, the growth spurt peaks at 11.5 yr at a top velocity of 8.3 cm (3.8 in) per year and then slows to a stop at 16 yr (see Fig. 104-5). In the average boy, the growth spurt starts later, peaks at 13.5 yr at 9.5 cm (4.3 in) per year, and then slows to a stop at 18 yr. Weight gain parallels linear growth, with a delay of several months, so that adolescents seem first to stretch and then to fill out. Muscle mass also increases, followed approximately 6 mo later by an increase in strength; boys show greater gains in both. Lean body mass, approximately 80% in the average prepubertal child, increases to 90% in boys and decreases to 75% in girls as subcutaneous fat accumulates.

Boys with SMR3 pubic hair and SMR4 genitals normally have their peak growth spurts ahead of them; girls at the same SMR are usually past their peaks (see Figs. 104-3 and 104-4). Widening of the shoulders in boys and the hips in girls is also hormonally determined. Other changes include a doubling in heart size and lung vital capacity. Blood pressure, blood volume, and hematocrit rise, particularly in boys. Androgenic stimulation of sebaceous and apocrine glands results in acne and body odor. Physiologic changes in sleep patterns and requirements may be mistaken for laziness; adolescents have difficulty falling asleep and waking up, especially for early school start times as opposed to typical self-regulated or preferred sleep schedules.

Menarche is achieved by 30% of girls by SMR3 and by 90% by SMR4 (95% of girls reach menarche at 10.5-14.5 yr of age). Menarche usually follows approximately 1 yr after the growth spurt begins. It is very common for cycles to be anovulatory during the 1st 2 yr after menarche (approximately 50%). The timing of menarche, which is not completely understood, appears to be determined by genetics as well as by factors such as adiposity, chronic illness, nutritional status, type and amount of exercise, and emotional well-being. Before menarche, the uterus achieves a mature configuration, vaginal lubrication increases, and a clear vaginal discharge appears (physiologic leukorrhea). In boys, the phallus lengthens and widens during SMR3, and sperm are usually apparent in semen.

Cognitive and Moral Development

With the transition to formal logical thinking, middle adolescents start to question and analyze extensively. Young people now have the cognitive ability to understand the intricacy of the world they live in, self-reflect, see beyond themselves, and to begin to understand their own actions in a moral and legal context. Questioning of moral conventions fosters the development of personal codes of ethics, which may be similar to or different from those of their parents. An adolescent’s new flexibility of thought can have pervasive effects on relationships with the self and others.

Self-Concept

Middle adolescents are more accepting of their own body changes and become preoccupied with idealism in exploring future options. Affiliation with a peer group is an important step in confirming one’s identity and self-image. It is normal for middle adolescents to experiment with different personas, changing styles of dress, groups of friends, and interests from month to month. Many philosophize about the meaning of life and wonder, “Who am I?” and “Why am I here?” Intense feelings of inner turmoil and misery are common. Girls may tend to characterize themselves and their peers according to interpersonal relationships (“I am a girl with close friends”), whereas boys may focus on abilities (“I am good at sports”). Adolescents of both genders, but especially boys, who develop later than their peers may experience poorer self-image and have higher rates of difficulty in school.

Relationships with Family, Peers, and Society

Middle adolescence refers to “stereotypical adolescence.” Relationships with parents become more strained and distant due to redirected energies toward peer relationships and separation from the family. Dating can become a lightning rod for parent-child battles, in which the real issue may be the separation from parents rather than the particulars of “with whom” or “how late.” The majority of teenagers progress through adolescence with minimal difficulties rather than experiencing the stereotypical “storm and stress.” It is the minority of adolescents (approximately 20-30%) who do experience stress and struggle through this period who require support. Adolescents with visible differences are also at risk for problems, such as not developing adequate social skills and confidence and having more difficulty establishing satisfying relationships.