The physical changes that accompany sexual maturation are called puberty. Although puberty is a universal feature of adolescence, individuals develop physically at different ages and at different rates. For example, in the United States, girls reach menarche (the time of first menstruation) at an average age of 12, but in New Guinea, the average age is 18. Both genetic and environmental factors play a part in determining the onset and duration of puberty.
Rapid acceleration in growth, the further development of the gonads, the development of secondary sex characteristics, changes in body composition, and changes in the respiratory and circulatory systems.
The Endocrine System: Puberty is a gradual process that begins at conception. The endocrine system produces, circulates, and regulates levels of hormones that are already present since birth. These hormones perform both an organizational role (e.g., organize or program the brain to behave in certain ways) and an activational role (e.g., activate changes in behavior) during adolescent development.
During infancy a feedback loop develops involving the pituitary gland (which controls hormone levels), the hypothalamus (the part of the brain that controls the pituitary gland), and the gonads (in males, the testes; in females, the ovaries). At puberty a change occurs in the hypothalamus such that it takes higher and higher levels of androgens and estrogens to trigger the hypothalamus (known as the system's set point). The hypothalamus then stimulates the pituitary gland, which in turn stimulates the gonads to produce more androgens and estrogens.
Both sexes produce androgens and estrogens (the sex hormones released by the gonads), however, the average male typically produces more androgens than estrogens while the average female produces more estrogens than androgens.
What Triggers Puberty? Although the increased secretion of these sex hormones is one of the most important endocrinological changes to occur at puberty, it is not the only one. The hypothalamus also controls changes in the secretion of hormones that act on the thyroid and the adrenal cortex. These hormonal changes stimulate many of the changes in stature and bodily dimensions characteristic of the period. In addition, recent research indicates early feelings of sexual attraction may be stimulated by adrenarche (the stimulation of the adrenal glands).
SOMATIC DEVELOPMENT
Changes in Stature and the Dimensions of the Body: Increases in the levels of hormones lead to the adolescent growth spurt, which occurs about 2 years earlier in girls than in boys. During peak height velocity, an adolescent is growing at approximately the same rate as a toddler (about 4 inches per year for boys and 3.5 inches per year for girls).
The asynchronicity in growth of body parts during early adolescence often result in a clumsy or gawky appearance. In addition to sheer changes in height and weight, there are changes in the relative proportion of body muscle and body fat, and changes in the circulatory and respiratory systems. Sex differences in these latter areas are especially important, since such differences are minimal prior to adolescence. For example, body fat in boys tends to decrease whereas in girls it tends to increase. Many girls react to the increase in body fat at puberty by dieting unnecessarily.
Sexual Maturation: Another important aspect of somatic development at puberty is the emergence of reproductive capability and the development of secondary sex characteristics (changes related to physical appearance). The sequence of changes (often referred to as Tanner stages) is more orderly for males than for females.
Sexual Maturation in Boys: In boys, the changes in physical development occur in the following order: rapid growth of testes and scrotum and appearance of pubic hair; the beginning of the growth spurt, enlargement of the penis and thickening of pubic hair; growth of facial and body hair and lowering of the voice. The first ejaculation usually occurs about a year after the beginning of the accelerated growth of the penis.
Sexual Maturation in Girls: Girls' development is in a less regular sequence, but usually begins with the development of the breast buds or growth of pubic hair. Later, breasts develop nipples and areola (the area around the nipple) and enlarge, and pubic hair thickens. Menarche, the first menstrual period, occurs later in puberty, and ovulation and the ability to carry a baby to full term usually follow menarche by several years, although it is possible for a girl to become pregnant at any time following her period.
TIMING AND TEMPO OF PUBERTY
Variations in the Timing and Tempo of Puberty: There are tremendous variations among individuals in the timing (i.e., age at onset) and tempo (i.e., rate of change) of puberty. Some individuals will have completed pubertal maturation before their same-age peers will have even begun puberty.
Genetic and Environment Influences: Generally speaking, studies indicate that individuals who are closely related genetically have similar patterns of pubertal timing and tempo. However, genetic influences on pubertal growth are better thought of as creating a predisposition to mature at a given time and at a given rate rather than as determining a fixed absolute.
Individual Differences in Pubertal Maturation: Although the most important influence on the timing of maturation is genetic, adolescents who have been well-nourished and healthy during childhood go through puberty earlier than their less fortunate peers. Recent studies suggest that social factors may also influence the onset of maturation. For example, family conflict and stress may accelerate the pubertal process while living in the proximity of one's biological relatives appears to slow it down.
Group Differences in Pubertal Maturation: The age at which adolescents mature physically varies around the world. On average, teenagers in highly industrialized countries, like Japan, mature earlier than their counterparts in developing nations, where health and nutritional problems slow growth. The age at menarche has declined considerably over the past 150 years, a phenomenon known as the secular trend, which may be attributed to improved nutrition, better sanitation, and better control of infectious diseases.
THE PSYCHOLOGICAL AND SOCIAL IMPACT OF PUBERTY
Two approaches can be taken to studying the psychological and social consequences of puberty. Longitudinal studies identify a group of subjects of the same pubertal stage and then follow them for a period of time, often over several years. In cross-sectional studies, researchers select groups of individuals who are at different stages of puberty and then compare these groups to one another.
The Immediate Impact of Puberty: Regardless of whether puberty occurs early or late, physical maturation has been found to affect the adolescent's self-image, mood, and relationships with parents. Self-esteem has been found to decline among girls who are going through puberty but only when accompanied by other changes that require adaptation (e.g., dating, changing schools). Puberty has also been associated with increases in negative moods but only during the early stages of puberty when hormone levels are fluctuating widely. Furthermore, physical maturation increases distance between parents and adolescents and has been linked to adolescent sleep patterns of staying up late and sleeping in, referred to as the delayed phase preference. More important than puberty itself is how puberty is viewed within the context in which the adolescent matures, and the extent to which the adolescent has been prepared psychologically for the biological changes of puberty.
The Impact of Specific Pubertal Events: Most adolescents respond positively to the changes associated with puberty. Girls' attitudes, however, still vary, with those who view menarche negatively experiencing the most discomfort. Far less is known about males' reactions to first ejaculation. In contrast to girls, boys tend not to discuss this experience with either parents or friends.
The Impact of Early or Late Maturation: Researchers have also examined the impact of early and late maturation. Generally speaking, early-maturing boys may have some short-term advantages (e.g., during adolescence itself, early maturers are more popular and confident), but some long-term disadvantages (e.g., during adulthood, men who were early maturers are more conventional and conforming). For girls, it may be more advantageous--at least in terms of popularity--in the short run to be either somewhat late or to mature around the same time as one's peers. In the long run, however, early-maturing girls may show some psychological benefits, in that they appear to develop more sophisticated coping skills. For both sexes, however, early physical maturation is associated with more problem behavior, including drug and alcohol use, delinquency, and precocious sexual activity.
EATING DISORDERS
Eating attitudes and behaviors that are considered unhealthy are referred to by psychologists as disordered eating. These can range from a preoccupation with weight to a clinical eating disorder. Weight gain during puberty due, in part, to the drop in the body's basal metabolism rate may cause adolescents (especially girls) to become extremely concerned about their weight. Many U.S. adolescents, however, have legitimate concerns about gaining weight, 20% of are overweight; 5% are obese.
Anorexia Nervosa and Bulimia: Bulimia is an eating disorder characterized by a cycle of bingeing and purging while anorexia nervosa exhibits symptoms of extremely restrictive self-induced diet. Although the incidence of anorexia and bulimia is small, it is far more common among females than males, and is rarely seen before puberty. Contrary to previous reports, recent research does not exclude any social class or ethnic group from the likelihood of developing an eating disorder. Several theories have been proposed to account for the emergence of eating disorders, ranging from biological to environmental or interplay between the two.
PHYSICAL HEALTH AND HEALTH CARE IN ADOLESCENCE
Adolescent health care has become a salient issue in the last two decades due to the prevalence of risk-taking behaviors in this age group. Although adolescence is characterized as one of the healthiest periods in the life span, the "new morbidity and mortality" of adolescence indicate that adolescent health problems are often psychosocial in nature. Contributors to this new morbidity and mortality include automobile accidents, violence, substance abuse, and unprotected sex.
New approaches to adolescent health care emphasize health promotion by reducing health-compromising behaviors (e.g., drinking and driving) and increasing health-enhancing behaviors (e.g., wearing seat belts). Among the most important innovations are school-based health centers.
Any successful health promotion program for adolescents should include the "five A's": anticipatory guidance, ask, advise, assist, and arrange.
