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Adolescence, 6/e
Laurence Steinberg, Temple University

The Fundamental Changes of Adolescence
Biological Transitions

Chapter Outline

  1. Puberty: an overview.
    • Puberty is primarily a stage of physical development, through which an individual becomes capable of sexual reproduction.
    • There are five chief physical changes that take place during puberty:
    • Rapid acceleration in growth (height and weight)
    • Development of primary sex characteristics (organs that allow reproduction)
    • Development of secondary sex characteristics (external characteristics that signal maturation)
    • Changes in body composition (fat and muscle)
    • Changes in circulatory and respiratory systems (strength and stamina)
    1. The endocrine system.
      • Endocrine glands produce and regulate levels of hormones in the blood.
      • Hormones are chemicals secreted by the endocrine glands.
      • Body tissues selectively "perceive" the instructions of hormones. For example, adrenaline affects the heart in ways it does not affect other tissue.
      • Some hormones have been present since the fetus was developing in the womb.
      • The brain (central nervous system), and specifically the hypothalamus, monitors the levels of hormones in the blood, and maintains a set point or specific level of hormones. The hypothalamus is the "thermostat" of the hormonal system.
      • The hypothalamus, pituitary gland, and the gonads (ovaries, testicles) operate in a "feedback loop," producing and maintaining the levels of sex hormones (androgens and estrogens) that are mainly responsible for the primary and secondary changes of puberty.
      • The interaction between the hypothalamus, pituitary gland, and gonads is called the HPG axis.
      • The hypothalamus "reads" the levels of hormones and instructs the pituitary gland to release more or less of them. The pituitary gland then instructs the gonads to produce more or less androgens or estrogens. When the hypothalamus perceives there is a high enough level of sex hormones in the blood, it tells the pituitary gland to stop increasing the levels of hormones.
      • Both androgens and estrogens are produced by each gender. During adolescence, the average male produces more androgens and the average female produces more estrogens.
      • Hormones perform an organizational role and an activational role during adolescence. Hormones organize the way the brain is shaped as it is growing, and hormones activate (turn on) changes in behavior at different times during one's life.
      • The human brain is "feminine" until about 8 weeks after conception when it is exposed to certain "masculinizing" hormones, like testosterone.
      • This change in brain formation influences behavior later in life, such as aggression.
      • During puberty, hormones activate changes in secondary sexual characteristics, such as pubic hair.
      • The organization and activation influences of hormones interact with one another.
    2. What triggers puberty?
      • Rising levels of leptin, a protein produced by fat cells, may signal changes that occur during puberty.
      • It seems that a certain level of body fat, and leptin, may instruct the hypothalamus to initiate the hormonal changes that signal the onset of puberty.
      • The pituitary gland also secretes hormones that influence the thyroid gland and the adrenal cortex to release hormones that stimulate overall body growth.
      • Maturation of the adrenal glands, called adrenarche, may also stimulate sexual attraction.
  2. Somatic Development
  3. The average teen grows 12 inches taller during puberty.

    1. Changes in stature and the dimensions of the body
      • Adolescent growth spurt - increase in height and weight
      • The speed of the spurt is dramatic.
      • Peak height velocity for males is approximately 4.1 inches per year; for females it is approximately 3.5 inches per year.
      • Growth spurt occurs, on average, two years earlier in females than males.
      • One indication of the end of pubertal growth is the closing (hardening) of the long bones in the body.
      • Bones become much harder after the growth spurt. Those of African-Americans are harder than those of Caucasians, contributing to the fact that Caucasians are more likely to experience osteoporosis and bone fractures later in life.
      • Much of the height gain comes from increase in torso length.
      • The sequence of growth begins in the extremities (hands, feet) and moves inward, with the torso growing in size last.
      • The different timing in the growth of body parts is referred to as asynchronicity in growth.
      • Proportionately, males tend to gain more muscle weight, and females more body fat, over the course of puberty.
      • The difference in muscle-to-body weight proportions tends to allow males to outperform females in athletic events.
      • The difference in fat-to-body weight proportions tends to contribute to females' feelings of being overweight.
      • Females who mature early, begin dating early, and come from comparatively affluent families tend to experience less satisfaction with their body image.
      • Increases also occur in the size and capacity of the heart and lungs, facilitating better athletic performance.
      • While males typically achieve higher athletic performance after puberty, females are socialized away from physical activity.
    2. Sexual maturation
      • Secondary sexual characteristics, which are described by specific elements in the Tanner stages, occur as teens develop the external appearances of a man or a woman.
      1. Sexual maturation in boys
        • The sequence of physical changes for males typically begins with changes in the scrotum, testicles, and pubic hair, followed by a growth spurt in height and growth of the penis, followed by growth of facial hair, followed by changes in the vocal chords.
        • Changes in the skin and production of sweat and oils produces the acne experienced by many adolescents.
        • Changes in the primary sexual characteristics (changes to the internal organs and processes necessary for reproduction) influence the tendency for the first ejaculation of seminal fluid, which tends to occur about one year after the acceleration of penis growth.
      2. Sexual maturation in girls
        • The sequence of physical changes for females typically begins with changes in the breasts and pubic hair, but these are accompanied by a growth spurt in height. Menarche (the first menstrual cycle) is typically an event that occurs toward the end of pubertal changes. Regular ovulation tends to follow menarche by approximately two years.
  4. The Timing and Tempo of Puberty
    1. Variations in the timing and tempo of puberty
        • Females tend to start puberty between ages 7 and 13.
        • Males tend to start puberty between ages 9.5 to 13.5.
        • There is no set time period for the length of puberty.
        • African-American females mature earlier than Caucasian females.
    2. Genetic and environmental influences
      1. Individual differences in pubertal maturation
        • The timing and tempo of pubertal maturation are primarily influenced by one's genes.
        • Everyone inherits a tendency for change that is written in his or her genes, but the actual timing of pubertal changes can be influenced by factors other than genes.
        • The two most important external factors are nutrition and health.
        • Puberty occurs earlier for individuals who have been extremely well nourished throughout childhood, and for those who have not experienced significant illnesses.
        • Excessive exercise is also associated with delayed pubertal changes.
        • Puberty tends to occur earlier for teens that grow up in conflict-ridden families, and, for females, in father-absent homes.
        • It may be that low stress in the family may speed maturation, while high stress may impede maturation.
        • The presence of a stepfather may also expose adolescent girls to pheromones that stimulate pubertal maturation.
        • Living in close proximity to one's biological relatives appears to slow the process of pubertal maturation, while exposure to genetically unrelated members may accelerate maturation.
      2. Group differences in pubertal maturation
        • Average age of menarche is earlier in countries with better nutrition.
        • Females in affluent homes tend to reach menarche earlier than girls from poor homes.
        • The secular trend: in industrialized countries over the last 150 years, females have reached menarche at earlier ages.
        • While the secular trend has leveled off, some females experience puberty at very young ages (e.g., ages 6 or 7), and the average child reports feeling sexually attracted to others around age 10.
  5. The Psychological and Social Impact of Puberty
    • Hormones can directly affect behavior (e.g., sex drive).
    • Physical changes cause changes in self-image, which affect behavior.
    • Physical changes cause changes in how others treat the adolescent, which affects how the adolescent behaves.
    • Adolescent females' preoccupation with their bodies is a relatively recent phenomenon, influenced by marketers of clothing, cosmetics, and weight loss products.
    • Cross-sectional research allows scientists to examine different age groups at the same time, helping us understand age differences.
    • Longitudinal research allows scientists to examine the same group over time (as the subjects get older), helping us understand changes that occur as adolescents develop.
    1. The immediate impact of puberty
      1. Puberty and self-esteem
        • Going through puberty may lead to modest declines in self-esteem in girls, but only when accompanied by other life stressors (e.g., onset of dating, menarche, and changing schools in the same year).
        • Caucasian girls are most likely to develop an unsatisfactory body image. These girls are more likely to be concerned about the size of their hips, thighs, waist, and weight gain.
      2. Adolescent moodiness
        • Adolescents are stereotypically thought to be moodier than children or adults.
        • The "beeper study" determined that teens' moods do fluctuate more than adults'.
        • However, the direct connection between hormones and moods is not very strong.
        • It may be the fluctuation rather than the dramatic increase in hormones that influences moodiness.
        • While the moods of girls are related to levels of hormones, life stressors seem to be more important predictors of mood.
        • Adolescent mood swings seem to parallel changes in activities.
        • There may be 5 distinct patterns of mood changes:
        • Some teens have frequent mood fluctuations, but are generally happy.
        • Some teens have few fluctuations, and are generally happy.
        • Some teens have few fluctuations, but are generally in a bad mood.
        • Some teens have frequent fluctuations, and are generally in a bad mood.
        • Some teens have few fluctuations, but are in an extremely negative mood most of the time.
      3. Changes in patterns of sleep
        • Hormones may also affect the sleep needs of adolescents.
        • A delayed phase preference seems to exist, influenced by the biological changes of puberty.
        • Teens tend to stay up later and wake up later than either children or adults.
        • When left to their own schedule, most teens are awake until 1:00 a.m. and sleep until about 10 a.m.
        • Most scientists believe that most teens are not getting enough sleep, which is related to poorer mental health and lowered school achievement.
      4. Puberty and family relations
        • Puberty appears to increase the conflict and distance between parents and children.
        • This distancing is not as strong in single-parent homes and ethnic minority families.
        • Minor conflicts increase, and positive exchanges decrease, at least while the adolescent is going through puberty.
        • This change is not affected by the timing of puberty.
        • Developments during puberty seem to affect the balance of interpersonal relationships in the family system that existed during childhood.
        • As they mature, adolescents tend to name peers rather than adults (and parents) as the individuals who are most important to them.
    2. The impact of specific pubertal events
      • Most teens respond positively to the biological changes of puberty.
      • The attitudes of girls toward menarche has become more positive in recent years. The discussion of menstruation is more open than it has been in the past.
      • Menarche is typically accompanied by increases in social maturity, peer prestige, and self-esteem.
      • Girls with negative attitudes about the event, however, tend to experience greater menstrual discomfort.
      • A female's attitude toward menarche is also influenced by whether or not she is an early maturer; these girls tend to have more negative reactions to the event.
      • Less research has been conducted regarding the impact of first ejaculation on males, although existing research indicates it does not carry nearly as much anxiety for males as menarche does for females.
    3. The impact of early or late maturation
      1. Early versus late maturation among boys
        • Early-maturing boys tend to experience the changes in positive ways.
        • Late-maturing boys tend to have lower self-esteem than other boys.
        • Early maturers are more likely to get involved with antisocial activities, including drug and alcohol abuse.
        • There are advantages for late-maturing boys. They tend to have higher levels of intellectual curiosity, exploratory behavior, and social initiative when compared to early maturers after all individuals have completed puberty.
        • It may be that late maturers have had a longer period of time to "prepare" themselves for the changes of puberty.
        • Longitudinal research shows that, in early middle age, late maturers tend to be more responsible, cooperative, self-controlled, and more sociable, but are also more conforming, conventional, and humorless than late maturers.
      2. Early versus late maturation in girls
        • Early studies found that early-maturing girls were less popular, less poised, less expressive, and more submissive and withdrawn than other girls.
        • More recent research shows that early-maturing girls have more emotional problems, including problems with self-image, depression, anxiety, eating disorders, and panic attacks. These problems seem to be related to girls' feelings about their weight.
        • These findings tend not to apply to females in cultures such as Germany, where attitudes toward sexuality and appearance are not as important as they are in the U.S.
        • While self-image may suffer, early-maturing girls do not tend to lose ground in popularity.
        • Early-maturing girls may experience more difficulties because of the pressure they feel in relation to males, especially given the fact that early-maturing girls are more likely to associate with males who are older.
        • Early-maturing girls are also more likely to become involved in deviant activities such as drug and alcohol abuse.
        • However, early-maturing females who attend all-girl schools do not seem to experience the same difficulties.
        • Once they reach adulthood, early-maturing females tend to be more psychologically advanced than other females.
        • However, they tend to have lower educational aspirations.
  6. Pubertal Changes and Eating Disorders
    • Basal metabolic rate decreases about 15 percent during puberty.
    • Approximately 20% of females are currently overweight, and 5% are obese.
    • Obese adolescents will likely (80%) continue to be obese as adults, and this is accompanied by a variety of health risks (e.g., hypertension, high cholesterol, and diabetes).
    • Disordered eating patterns are common among adolescents.
    1. Anorexia nervosa and bulimia
      • Research indicates that serious weight control efforts (e.g., dieting, use of laxatives, deliberate vomiting) actually lead to weight gain rather than weight loss.
      • Girls whose mothers have body image problems, and girls who report more negative relationships with parents, are more likely to use problematic weight loss techniques.
      • Bulimia is a disorder characterized by overeating followed by self-induced vomiting (or the use of laxatives or excessive exercise) in order to avoid weight gain.
      • Anorexia nervosa is a disorder characterized by continued self-induced food deprivation.
      • Adolescents with either eating disorder have a disturbed body image.
      • Perhaps as many as 20% of anorexic adolescents starve themselves to death.
      • Approximately 0.5% of teens are anorexic, and 3% are bulimic.
      • Dissatisfaction with body image is pervasive among teenage girls, however.
      • Recent research shows that this problem is pervasive among females from a variety of ethnic and socioeconomic backgrounds.
      • Some theories of eating disorders point to genetic or hormonal differences, while others point to dysfunctional family dynamics (e.g., overcontrolling parents).
      • A third possible explanation is that eating disorders are but one aspect of a generalized psychological difficulty called internalized distress.
      • Finally, some scientists point to the socio-cultural pressure that is placed on females to be thin, a stressor that males do not experience as harshly.
      • While a variety of therapeutic techniques have been used to treat bulimia and anorexia, hospitalization is often required for successful treatment of anorexia.
  7. Physical Health and Health Care in Adolescence
    • Adolescence, in general, is a very healthy time of life.
    • However, it is also a time of great risk, because adolescents engage in behaviors that can result in health problems (drug use, aggression, unprotected sex, drunk driving).
    • While there have been dramatic improvements in medicine and treatment of childhood and adolescent illnesses, there is an increasing threat from unhealthy choices teens make (the "new morbidity and mortality of adolescence").
    • The death rate from violence and injury increased between 1950 and 1985.
    • Approximately 45% of teen deaths result from car accidents, and another 30% are a result of homicide or suicide.
    • Health promotion among adolescents has addressed the fact that most of the health and morbidity problems result from choices teens make regarding their own behavior (e.g., smoking, driving drunk).
    • Practitioners focus now on promoting health-enhancing behaviors and steering teens away from health-compromising behaviors.
    • Successful health promotion includes:
    • Establishing a trusting relationship with a teen prior to adolescence
    • Talking to teens about healthy and non-healthy behaviors
    • Offering sound advice about healthy behaviors
    • Encouraging teens to participate in health-promoting programs
    • Following up with teens after participation
    • School-based health centers now offer teens health services.
    • Studies show that teens' attitudes (at least) are often changed after the use of these health centers.
    • Minority youth are at greater risk for experiencing both "old" and "new" morbidities.
    • Homicide is the leading cause of death for African American adolescents.
    • American Indian/Alaska Native males are 4 times more likely to commit suicide.