How do hormones affect the physical and psychological aspects of puberty?

2.1 Pubertal Processes

Puberty is a series of processes involving the development of the hypothalamic–pituitary–gonadal axis (gonadarche), the adrenal system (adrenarche), and growth—culminating in reproductive maturity and adult anatomy and physiology. Psychological research tends to focus on the sex hormones that increase at puberty (especially estradiol in girls, testosterone in boys, and adrenal hormones in both sexes) and on the physical features that are influenced by these hormones (secondary sex characteristics). For example, estradiol influences breast development and menarche in girls, testosterone influences testicular development and voice changes in boys, androgens influence body hair in both sexes, and sex hormones and growth hormone influence height in both sexes.

Several points about pubertal development are important to consider in evaluating its role in psychological development. Different pubertal processes and their related features develop on somewhat different timetables (Susman et al., 2010; Tanner, 1978), with potentially differential value in terms of social signaling and personal salience. Adrenarche occurs earlier than gonadarche, with adrenarche occurring close to the same age in both sexes, but gonadarche occurring earlier in girls than in boys. The features of puberty develop in a fairly similar sequence for all youth, but there is considerable variability in the age at which they develop (their onset or timing) and their speed of development (tempo); there is also likely variability in the synchrony of development of different features but this has not been well studied (Mendle, 2014; Susman et al., 2010). For girls, breast development is typically the first sign of puberty and is visible to others, whereas menarche occurs late in puberty and is private. For boys, testicular enlargement is typically the first sign of puberty and is generally not apparent to others, whereas the height spurt (visible to others) does not occur until midpuberty.

Progression of pubertal development is generally described by Tanner stages (1–5) for the cardinal features: genitalia (breast in girls, penis and testis in boys), pubic hair, and height spurt (Tanner, 1962, 1978). Prepuberty is Tanner stage 1 and complete development is Tanner stage 5. Intermediate stages of development are described by Tanner stages 2–4. Midpuberty is Tanner stage 3 and is associated with the surge in gonadal hormones (estradiol in girls, testosterone in boys). Tanner stages for each feature clearly form an ordinal scale; it is not as clear that they form the interval scale typically used. For example, it is not known whether the difference in breast development between Tanner 2 and 3 is the same as that between Tanner 3 and 4.

Several aspects of the pubertal process are illustrated in Figure 1, which is taken from a classic work on physical development (Tanner, 1978). The figure shows the sequence of pubertal events in boys and girls described by Marshall and Tanner (1969, 1970) from data they collected in the 1960s. The figure is used here to illustrate points made earlier: girls mature earlier than boys, different features develop on different timetables, and there is considerable variability across children in the ages at which they reach different stages of puberty. These data come from a sample that is unique in several ways: it was the largest number of children studied longitudinally up to that point, but the children lived in family groups in a children's home, were of low socioeconomic status, and may not have received good care before they entered the home. Thus, caution is needed when making inferences to contemporary samples about specific events such as age at menarche, but the general pattern of results reported in this early study is consistent with recent data (e.g., Susman et al., 2010).

Skeletal Maturation

Puberty is also an important time for the development of bones. Specifically, substantial bone mineralization occurs. In fact, for girls, almost one-third of bone mineralization occurs during the pubertal period. Girls’ skeletal maturation occurs earlier than boys’, perhaps resulting in less bone mineralization (and density) in the typical girl than boy. If girls diet severely enough to develop amenorrhea, they may reduce the amount of mineralization. This means that their bones may be permanently weakened, although there is postpubertal mineralization. Failure to maximally develop bone strength during adolescence likely contributes to an increased risk of osteoporosis and dangerous bone fractures during later adulthood. Indeed, women who recover from anorexia nervosa may show evidence of osteoporosis in their 30s or 40s.

A Relatively Low BMD During Puberty

Puberty is a period of rapid skeletal growth that is genetically programmed and hormonally driven. The rate of total body bone mass accrual throughout adolescence was determined by Bailey et al. in a longitudinal study of white boys and girls [13]. From this study, we know that approximately 25% of adult peak bone mass is acquired over approximately 2 years—on average this occurs from age 12 to 14 years in girls and age 13 to 15 years in boys. Peak bone mineral content (BMC) velocity is higher and occurs later for boys than for girls. The timing of bone mineral acquisition is more closely linked to pubertal development than to chronological age [2,13].

During puberty, bones first elongate and then mineralization, or bone consolidation, ensues. At the age of peak height velocity, adolescents have acquired 90% of their adult height (or bone size) but only 60% of adult total body BMC. Thus, early puberty is a period of relatively low BMD and, therefore, susceptibility to fracture is not unlike that of age-related bone loss [14–16]. The higher incidence of fracture during this time of life corresponding to the lower BMD in the study by Bailey et al. [13] is shown in Fig. 44.4. Approximately 51% of boys and 40% of girls experience fractures by age 18 years [16].

The dramatic increase in rates of childhood fracture in the United States in just three decades is apparent in Fig. 44.5. Fracture incidence increased 32% in males, with the greatest increase at age 11–14 years, and 56% in girls, with the greatest increase at age 8–11 years. Increased rates of childhood fracture may relate to reduced consumption of milk, change in physical activity or recreational activities, and/or increased body weight during this time period. The prevalence of excessive adiposity in children and adolescents has nearly tripled while the incidence of fracture has increased [19]. In adults, increased weight has been associated with increased bone mass [20], but overweight children and adolescents have higher rates of fracture [12,21,22]. The increased incidence in fracture with excessive body weight in children has been hypothesized to occur because of greater force being placed on bones such as the radius during falls, lower bone mass and bone strength with increasing body fat when adjusted for total body weight, and impaired mobility [21,23–28]. The interaction between calcium intake and body mass index (BMI) is described later. Changes in bone geometry that accompany increases in bone size throughout childhood include increases in cortical thickness and bone diameter [29]. Bone diameter and cortical thickness are less in children with excess body fat [28]. This emphasizes the need to maintain ideal body weight in children.

III.B.2 Adolescence

During puberty, biology and learning interact in ways that increase the chances that teens will think, wonder, and fantasize about sex, leading increasing numbers of teens to experiment with sex with each passing year of age. Let us deal with biology first and then learning. During puberty, rising levels of adult sex hormones increase the sensitivity of the genitals and the sexual reflexes in both male and female bodies. Boys experience spontaneous penile erections during dream sleep, wet dreams, and various times during the waking day. Having a spontaneous erection can lead to masturbation. Adolescent boys report more spontaneous sexual arousal than do girls. This is in part because the penis is large enough that boys can easily notice their erections, whereas the female sexual responses of clitoral enlargement and vaginal lubrication are more subtle and difficult to notice.

Because the sexual hormones make the genitals more sensitive, stimulation to them is more pleasurable and reinforcing than it was in childhood. As a result, adolescents who explore sexual activities receive stronger rewards than they did in childhood, which leads them to think and fantasize about sex more often. These sexual thoughts and feelings lead many teens to seek sexual information from real and symbolic models or look for first-hand experience via sexual activities. As a consequence, many teens (especially boys) experience a rapid surge in learning more complex and lengthy chains of sex-related activities: how to talk with potential sexual partners, how to suggest physical intimacy, and how to explore all sorts of sex-related activities.

During adolescence, the differences between people who have learned to be erotophiles or erotophobes become especially noticeable. It is also clear that there is a continuum of responses to sex between erotophilia and erotophobia—between those people who like sex (and feel little guilt about it) and those people who feel guilt, anxiety, shame or phobia about sex. Generally, the more phobic people have so many aversive associations related to sex that they feel inhibited about seeking sexual information or education. However, their avoidance of sexual knowledge does not guarantee that they will know how to resist seductive sexual approaches by or from insistent partners. Many erotophobes have been talked out of their virginity by verbally persuasive individuals. Then we discover that erotophobes are not immune to the painful consequences of uninformed sex, such as pregnancy and sexually transmitted diseases (STDs), and their avoidance of sexual education actually puts them at a greater risk of problems than their better educated peers. All through history, many teens who have been told to remain virgins until marriage have disobeyed, experimented with sex, become pregnant and been forced into marriage, abandoned by their families, or worse.

Pubertal Status

Adolescence, and puberty in particular, is a challenging time for young people, especially for young women, who are at risk for low self-esteem and dissatisfaction with body shape and weight. Puberty is generally a more positive experience for young males, as the weight and shape changes they experience are often desired, with some males desiring to build up their bodies. Body image views and concerns that appear prior to puberty may be with respect to eating/dieting, activity, and body image.

It has been postulated that with age body satisfaction decreases for females and increases for males. During puberty, males and females experience various changes to their bodies and they are more attentive to changes during this period, particularly changes in weight and shape. Girls experience a normative increase in body fat, which causes them to have about twice as much body fat as boys. This decrease in body satisfaction in females is not surprising given that puberty moves females away from the sociocultural thin ideal for women. Conversely, puberty for males brings about changes such as increases in muscularity that inevitably bring them closer to the societal muscular ideal male body, which could explain the increase in body satisfaction for young males.

Some interesting research highlights the associations between self-concept, weight, pubertal development, and gender. An Australian study found that higher weight students had lower self-concept, and that postmenarcheal females had the poorest perceptions of their physical appearance. Self-concept scores were significantly related to body weight, and an interaction was observed between puberty and gender, such that postpubertal males had the highest and postmenarcheal females had the lowest self-concept scores. Hence, puberty may have opposite effects on the self-esteem of male and female adolescents. This supports the suggestion that the stage of pubertal development may be more important than age in influencing the self-concept of adolescents, particularly for females.

2.1 Six Basic Sex Differences

During puberty, both boys and girls begin to have increasing numbers of experiences with spontaneous sexual responses and nocturnal orgasms (triggered by unconscious mechanisms deep in the brain), but there are several major sex differences in these hormonally induced changes. First, pubertal boys begin to have spontaneous sexual arousal 2 to 3 years before girls do, giving boys a significant head start over girls in learning about sex. Second, pubertal sexual arousal is more noticeable and distracting for boys than for girls. A boy who has a spontaneous penile erection is far more likely to notice this conspicuous change than a girl is to notice when she has spontaneous clitoral enlargement and lubrication in the vagina. The girl’s response is subtler and more difficult to notice, whereas the boy’s response is bigger in that as his penis elongates from 3 or 4 inches (the average length before stimulation) to approximately 6 inches (the average length once erect). Because the boy’s penis is well endowed with nerves that connect to the reward centers of his brain, the boy is likely to associate sexual arousal with pleasure. Even though the girl’s genitals also connect to the pleasure centers in her brain, the subtly of female sexual responses makes them less noticeable and less likely to create the powerful positive sexual conditioning that boys experience. Third, boys are significantly more likely to experience spontaneous nocturnal orgasms than are girls. Among young people who experience nocturnal orgasms, boys report them approximately four times more frequently than do girls. These orgasms are often associated with sexual dreams, and this strengthens the Pavlovian conditioning that links erotic images with sexual feelings, especially for boys. Fourth, boys experience nocturnal orgasms at a younger age than do girls, giving boys another major head start in sexual learning.

All four of these biological differences lead pubertal boys to become more curious about and interested in sex sooner than do same-age girls, although there is much variability among both boys and girls in the frequency and time of onset of all four of these experiences. Superimposed on these pubertal changes are all of the different levels of inhibitions or positive associations that each individual has learned about sex from his or her parents, family, and culture, with the double standard tending to create more sexual inhibitions for girls than for boys. This interaction of nature and nurture tends to produce the male–female differences in sexual interest shown by the bell-shaped curves illustrated in Fig. 1. The different shapes of the two skewed bell curves show that teen boys tend to be more interested in sex than are same-aged teen girls while also revealing considerable variability in the sexual interest of both boys and girls. For example, some girls fall near the right end of the continuum, indicating that they have more sexual interest than do all of the boys who are to their left on the continuum.

Adolescence brings about two additional concerns about girls' sexuality that can affect their sexual behavior. Sexually active girls tend to worry more about unintended pregnancies—and, in some cases, the issues related to abortion—than do most boys. Also, STIs can cause more serious damage to the reproductive organs of girls than to those of boys; hence, sexually active girls tend to worry more about the risk of contracting STIs than do sexually active boys.

What causes physical and mental effects during puberty?

What are the psychological effects of puberty?