Chapter 3

The Neuroendocrine System

The Neuroendocrine System: This system consists of glands within the body that produce hormones and structures within the central nervous system that regulate their activity. Neuroendocrine activity is regulated by a feedback system that controls the timing of puberty.
Key Terms: neuroendocrine system, hormones, androgens, testosterone, estrogens, estradiol, progesterone, adrenarche, gonadarche

Prepuberty: Adrenarche: Puberty occurs over two distinct phases, and the first, adrenarche, begins at 6 to 8 years of age and involves increased production of adrenal androgens that contribute to a number of pubertal changes—such as skeletal growth.
Key Terms: adrenal androgens

Puberty: Gonadarche: The second phase of puberty, gonadarche, begins several years later and involves increased production of hormones governing physical and sexual maturation.
Key Terms: hypothalamus, gonadotropin-releasing hormone (GnRH), anterior pituitary, gonads, luteinizing hormone (LH), follicle-stimulating hormone (FSH), GnRH pulse generator, kisspeptin, leptin

The Physical Changes of Puberty

Recollections of an Adolescent Girl: In girls, the appearance of pubic hair is one of the first visible signs of pubertal change. Breasts begin to develop at about the same time, along with the uterus, vagina, and ovaries.
Key Terms: primary sex characteristics, secondary sex characteristics

Recollections of an Adolescent Boy: For boys, who begin puberty an average of two years later than girls, the first sign of change is an enlargement of the scrotum, followed by the appearance of pubic hair. The penis starts to grow a year later. The height spurt precedes a change in voice and the appearance of facial and underarm hair.

The Growth Spurt: The growth spurt is a period of rapid growth in height, regulated by the growth hormone and the sex hormones. In girls, the most rapid growth occurs in the year preceding and the year following menarche. Boys reach their peak growth rate two years later than girls and grow for a longer period of time.
Key Terms: growth spurt

The Reproductive System: For girls, the uterus, the ovaries, and the vagina all increase in size. The ovaries increase their production of female sex hormones, and these hormones, with FSH and LH, stimulate the development of ova, or eggs. FSH and LH also stimulate the testes to develop in boys and produce male sex hormones. These, along with FSH, stimulate the testes to produce sperm. The penis doubles in length and thickness during puberty.
Key Terms: ovaries, ova, uterus, vagina, cervix, hymen, clitoris, glans, shaft, prepuce, testes, sperm, circumcision, female genital mutilation (FGM), outer labia

Menarche: Menarche, the onset of menstrual periods, occurs midway through puberty. Most girls reach menarche in their 12th year. The menstrual cycle is regulated by a feedback loop involving the ovaries, the anterior pituitary, and the hypothalamus.
Key Terms: menarche, anovulatory

Spermarche: In boys, the presence of testosterone and other hormones stimulates the testes to produce sperm. Most boys experience spermarche, the first ejaculation of seminal fluid, by mid-adolescence.
Key Terms: spermarche, nocturnal emission

The Secular Trend: Puberty begins earlier today than in past generations. This downward shift in age is called the secular trend. Adolescents also grow faster and grow to be larger than in the past. Improved nutrition is almost certainly an important cause of the accelerated growth patterns.
Key Terms: secular trend

The Psychological and Social Implications of Puberty

Heightened Emotionality: Adolescence is a time of heightened emotionality. Adolescents experience more intense emotions than their parents and report a wider range of emotions.

Relationships with Parents: Adolescents who experience their parents as warm and loving experience fewer emotional or behavioral problems. For most adolescents, however, closeness with parents temporarily decreases and conflict increases. Ethnicity may be a factor, though, as research suggests puberty may involve less conflict with parents for Hispanic vs. European American males.

The Timing of Change: Early and Late Maturers

Early and Late Maturing Boys: Differences in the timing of pubertal change are referred to as asynchrony. Comparisons of early and late maturing boys find initial social advantages for early maturing boys, but also more adjustment problems.
Key Terms: asynchrony, early maturation, late maturation

Early and Late Maturing Girls: In contrast to boys, early maturation in girls carries few initial advantages. Like boys, however, early maturing girls experience more problems of adjustment. Ethnic differences suggest these are less likely among African Americans. Three explanations have been offered for the more disruptive effects of early timing, particularly with respect to girls: the maturational deviance hypothesis, the stage termination hypothesis, and the adult status hypothesis.
Key Terms: self-esteem, maturational deviance hypothesis, stage termination hypothesis, adult status hypothesis

Body Image and Self-Esteem: Pubertal changes bring about changes in adolescents’ body images. How satisfied adolescents are with their bodies is also influenced by their perceptions of how they are evaluated by others. Females generally have less positive body images than males.
Key Terms: body image

Health and Well-Being

Nutrition: Despite the increased nutritional needs introduced by rapid growth, many adolescents eat erratically. Nearly half of all meals eaten in the U.S. are eaten in restaurants, most of which are fast-food chains. The biggest problem is not failing to get necessary nutrients, but getting too many other things along with them. Fast foods taste good because of excess fats, sugars, and salt; but these ingredients add calories—and with these, increased risk of becoming overweight.

Sleep: Patterns of sleep change as adolescents enter puberty. Adolescents fall asleep later and have difficulty waking up early—a pattern at odds with most high schools, which start earlier than middle or elementary schools. Consequently, a majority of adolescents fail to get enough sleep during the school week, and experience more difficulty paying attention and staying awake to study than do those just a few years younger.

Physical Activity: Regular physical activity contributes to adolescents’ health through building and maintaining bones and muscles and controlling weight, and by reducing stress and improving self-esteem. Even so, older adolescents are less active than younger ones.

Overweight: The number of adolescents who are overweight has tripled since the 1970s, with an estimated 17.6% of 12- to 19-year-olds currently overweight, and another 16.5% who are at risk of becoming overweight. Overweight adolescents are more likely to eat irregularly and faster, and exercise less than adolescents who are not overweight. This relationship highlights the importance of exercise in weight reduction programs.
Key Terms: overweight, body mass index (BMI)

Health Care: As an age group adolescents and young adults report poorer access to health care than young children or older adults. Problems are magnified for those living in rural communities or non-urban settings who are less likely to have health care insurance. Presently, approximately 9 million children and adolescents in the U.S. do not have health insurance. Yet more than half of these could receive free health insurance either through Medicaid or the Children’s Health Insurance Program (CHIP).

Poverty: Perhaps the single most important factor affecting the health and well-being of adolescents in the U.S. is poverty. Approximately 20% of U.S. adolescents live in poor families, with incomes below the federal poverty level, and another 12% in low-income families. These adolescents experience greater exposure to toxins, both inside and outside their homes, and live in more hazardous neighborhoods. The conditions of poverty are strongly related to stress, and to elevated levels of risk-related injuries. Solutions to their health needs will require the nation’s creative attention, since the conditions contributing to their poverty do not necessarily reside within their families.
Key Terms: poor families, low-income families