Chapter 1. Puberty

Synopsis

Rebecca Griffith, College of the Sequoias

Thomas E. Ludwig, Hope College

Catherine Robertson, Grossmont College

The Cycle of Hormones

Hormones are responsible for the outwardly visible signs of puberty and for the pubertal changes occurring within the body. Puberty is marked by a very noticeable growth spurt in both height and weight as well as by the development of primary and secondary sex characteristics. While not directly related to reproduction, secondary sex characteristics, such as the growth of pubic and underarm hair, are highly visible developments. In contrast, the less visible but equally important primary sex characteristics include the maturational changes to the reproductive organs. Hormones are involved in all of these changes.

The trigger for this rapid growth and sexual maturation is a signal from the hypothalamus area of the brain, which activates the nearby pituitary gland and sets up a domino effect. The outpouring of hormones from the pituitary produces reactions from the adrenal glands and the gonads, which are the testes in males and the ovaries in females. Before puberty and after, the gonads are producing estrogen and testosterone. At puberty, however, the female’s ovaries dramatically increase their production of estrogen by about eight times the previous rate while the male’s testes dramatically increase the production of testosterone by about 18 times the previous rate. A definite, noticeable growth spurt occurs simultaneously as the signals from the estrogen and testosterone circulate back to the pituitary gland and the hypothalamus. This feedback results in increased production of growth hormones, which in turn cycle back to trigger further production of estrogen and testosterone as adolescent organs are growing and maturing.

Puberty Milestones for Girls

Remarkable changes take place in a girl’s body during puberty. The table on this screen details some of the major developments of puberty and the average age of their onset. In girls, hormonal changes that precede and trigger the physical changes of puberty may start as early as age 9 on average. By age 16, many female adolescents have reached the end of puberty and are biologically fully developed women.

Puberty Milestones for Boys

Boys follow a similar but somewhat delayed path as compared to girls. The average boy enters puberty between 10 and 14 years old. Their weight spurt occurs about a year and a half later than that of girls. The peak height spurt and muscle and organ growth for males is quite a bit later than that of females. By age 18, the adolescent male is biologically a fully developed man.

Factors That Influence the Timing of Puberty

All of us reading this text have at least one thing in common. We all have experienced the sometimes exciting and often embarrassing journey of morphing from child to adult. Puberty, a period marked by accelerated growth and sexual maturation, happens to adolescents all around the world. Since puberty consists of a series of changes that occur gradually over several years, it is difficult for researchers to determine exactly when puberty begins or ends for a particular individual. On average for today’s children, the events of puberty usually begin between ages 8 and 14.

The onset of puberty may vary considerably from one person to another. Some individual variation is related to gender. On average, puberty begins one or two years earlier in girls than in boys. Genetic inheritance is a factor as some families tend to mature earlier or later than the average. Stress can also affect the timing of events. While undue stress can slow down a young child’s growth and production of hormones, stress in certain areas, such as family life and community life, may actually push anadolescent into early puberty.

Factors That Influence the Timing of Puberty (continued)

One very intriguing correlation connects the onset of puberty to body mass. Girls have more body fat as they begin to mature than boys do, which may relate to their earlier maturation. More telling, perhaps, are several studies indicating that overweight girls tend to mature earlier than girls of lower weights. If true, this finding might help explain the significant increase in the number of early maturing girls in the United States and Europe. While there are genetic variations that can lead to individual examples of thin girls menstruating earlier than their heavier friends, it appears that the hypothalamus somehow monitors body weight or body fat and triggers puberty in a female who has attained a body size that is capable of sustaining a pregnancy. The primary evidence for this “weight hypothesis” comes from two related findings:

1. In general, slender girls begin menstruating at a later age than heavier girls.
2. On average, girls begin menstruating when they attain a body weight of 100 to 104 pounds.

Furthermore, historical trends provide an argument in support of the weight hypothesis as well. It appears that the age of menarche in industrialized nations was around age 16 in the mid‐1800s and then steadily dropped over the next century to below age 13 by 1970. Medical records from the mid‐1800s suggest that the average European girl reached 100 pounds at about age 16 whereas today’s females reach 100 pounds by about age 12 or so.

Ethnicity and the Timing of Puberty

Research conducted by Adair and Gorden‐Larsen found a correlation between ethnicity and obesity for early maturing girls. For example, African‐American girls are almost three times more likely to be overweight than non‐white Hispanic girls, and these African‐American girls are more likely to begin their periods by the age of 11, which is 1.5 years earlier than the average. At the opposite end of the spectrum are the lighter‐weight Asian‐American girls who generally do not reach menarche until the age of 14, approximately 1.5 years later than the average.

Effects of Late and Early Puberty in Girls

In contrast, early maturation has the potential to introduce significant stresses in girls. Early‐maturing girls may be ridiculed by their male and female peers. Older boys and society in general may treat them as if they are older than they actually are. For example, older boys may approach them in sexual ways. Adults may expect them to assume more responsibilities or to behave in more grown‐up ways because of how their bodies look. In these scenarios, early‐maturing girls may be faced with situations, decisions, and challenges that far exceed their actual maturity levels. These early‐maturing girls often demonstrate signs of distress, such as depression, anxiety, eating disorders, lower academic achievement, succumbing to peer pressure, or engaging in high‐risk behaviors.

The way that girls respond to changes in their bodies may depend on the degree of parental support, their abilities to talk with peers about puberty, and the timing of their puberty relative to other girls in their peer group. A girl with a strong support system is more likely to be independent and eventually more satisfied with her body than girls who lack such support.

Effects of Late and Early Maturation on Boys

Boys who mature early may escape the kinds of social repercussions that girls encounter. Their comparatively early growth spurt and sexual maturity may earn them what some teens call “bragging rights” and the acceptance of older peers and even adults, whom they more closely resemble. Peers may look to these early‐maturing boys for leadership. Like girls, how a late‐ or early‐maturing boy handles his timing of puberty depends to a great degree on the support that he receives from family and peers. Late maturation may be less stressful for boys who are able to develop skills in other areas that make them feel competent, such as athletics, academics, computers, drama, or music.

Assessment: Check Your Understanding

Assessment: Check Your Understanding

Assessment: Check Your Understanding

Assessment: Check Your Understanding

Assessment: Check Your Understanding