Chapter 1. Puberty

Synopsis

Human Development Video Activity
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You must read each slide, and complete any questions on the slide, in sequence.
estrogen
Hormone produced primarily by the ovaries that is important for female development, reproduction, and sexual behavior.
gonads
Reproductive organs that produce gametes and sex hormones. The female gonads are the ovaries, and the male gonads are the testes.
growth hormones
Produced in pituitary gland to stimulate growth in the body during childhood and adolescence and to help regenerate and maintain organs and tissues throughout life.
menarche
The first menstruation in girls.
ovaries
A pair of reproductive organs in women located in the pelvis. Ovaries are responsible for producing hormones and eggs, the female gamete.
primary sex characteristics
Bodily organs that are directly involved in fertility and conception, including the vagina, uterus, ovaries, testicles and penis. While these organs are present at birth, they do not reach maturity until puberty.
puberty
The period of human development when the body grows and matures into adulthood. The sexual organs mature as the body readies for the possibility of reproduction.
secondary sex characteristics
Traits that are not directly related to fertility and conception that develop during puberty, such as breasts in girls, facial hair and a deepened voice in boys, and pubic and underarm hair in both sexes.
testes
Also known as testicles. A pair of reproductive organs in men located in the scrotum. Testes are responsible for producing hormones and sperm, the male gamete.
testosterone
Hormone produced primarily by the testes that is important for male development, reproduction, and sexual behavior.
A group of adolescents smiling at the camera

Puberty

Authors

A group of adolescents smiling at the camera

Rebecca Griffith, College of the Sequoias

Thomas E. Ludwig, Hope College

Catherine Robertson, Grossmont College

Synopsis

In this activity, you will explore the physical developments that take place leading up to and during puberty as girls and boys become women and men. You will learn what factors affect the timing of puberty and furthermore, any effects that experiencing puberty earlier or later than their peers may have on adolescents.

REFERENCES

Alsaker, F. (1992). Pubertal timing, overweight, and psychological adjustment. Journal of Early Adolescence, 12, 396‐419.

Elias, M. (August 7, 2001). Early puberty in girls linked to obesity, inactivity. USA Today.

Frisch, R. E., & Revelle, R. (1970). Height and weight at menarche and a hypothesis of critical body weights and adolescent events. Science, 169, 397‐398.

Herman‐Giddens, M., Slora, E., Wasserman, R., Bourdony, D., Bhapk, M., Koch, G., & Hasemeier, C. (1997). Secondary sexual characteristics and menses in young girls seen in office practice: A study from the Pediatric Research in Office Setting Network. Pediatrics, 99, 505‐512.

Kaplowitz, P., Slora, E., Wasserman, R., Pedlow, S., & Herman‐Giddens, M. (2001). Earlier onset of puberty in girls: relation to increased body mass and race. Pediatrics, 108, 347‐353.

Tanner, J. M. (1978). Foetus into man: Physical growth from conception to maturity. Cambridge, MA: Harvard University Press.

Young, C. H., Savola, K. L., & Phelps, E. (1991). Berkeley Growth Study. In Inventory of Longitudinal Studies in the Social Sciences (pp. 131‐133). Newbury Park, CA: Sage Publications.

The Cycle of Hormones

An illustration depicts some aspects of the cycle of hormones described on this screen.  A drawing of a male and female body points out the pituitary gland in the brain that releases hormones that stimulate the adrenal glands that reside just below the rib cage and the ovaries and testes.  Hormones from the adrenal glands and the ovaries stimulate the changes of puberty, which include growth of pubic hair, onset of menstruation, enlargement of the uterus, breast development, and growth of underarm hair in females and ejaculation, growth of the penis and testes, growth of pubic hair, enlargement of the larynx, and growth of facial and underarm hair in males.

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.

This table lays out the significant developments of puberty for girls and their approximate age of onset.  At approximately age 9, the ovaries increase production of estrogen and progesterone.  At approximately age 9 1/2, the uterus and vagina begin to grow larger.  At approximately age 10, breasts begin to develop.  At approximately age 11, pubic hair begins to appear, and a weight spurt begins. At approximately age 11 1/2, the height spurt reaches its peak.  At approximately age 12, females generally reach the peak of their organ growth and muscle development, and  their hips become noticeably wider.  At approximately age 12 ½, girls experience menarche, which is their first menstrual period.  At approximately age 13, girls have their first ovulation.  At approximately age 14, their voice lowers.  At approximately age 15, they develop their final pubic hair pattern.  At approximately age 16, they have full breast growth.  Please note that these average ages are rough approximations, with many perfectly healthy adolescents as much as three years ahead of or behind these ages.  Also, estrogen and testosterone influence sexual characteristics, including the potential for reproduction. Charted in this table are the increases in hormones produced by the gonads (sex glands). Adrenal glands produce some of both kinds of hormones (not shown).

Test Paragraph

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.

This table lays out the significant developments of puberty for boys and their approximate age of onset.  At approximately age 9 1/2, the testes increase production of testosterone.  At approximately age 10, the testes and scrotum grow larger.  At approximately age 11 1/2, pubic hair begins to grow.  At approximately age 12, the penis begins to grow.  At approximately age 12 ½, boys experience a weight spurt and their first ejaculation.  At approximately age 13, boys have their peak height spurt.  At approximately age 14, boys experience peak muscle and organ growth, and their shoulders become noticeably broader.  At approximately age 15, their voices lower, and facial hair becomes visible.  At approximately age 18, boys show the final pubic hair pattern.  Please note that these average ages are rough approximations, with many perfectly healthy adolescents as much as three years ahead of or behind these ages.  Also, estrogen and testosterone influence sexual characteristics, including the potential for reproduction. Charted in this table are the increases in hormones produced by the gonads (sex glands). Adrenal glands produce some of both kinds of hormones (not shown).

Test Paragraph

Factors That Influence the Timing of Puberty

This table lays out the significant developments of puberty for boys and girls and their approximate age of onset.  At approximately age 9 in girls, the ovaries increase production of estrogen and progesterone.  At approximately age 9 1/2, the uterus and vagina begin to grow larger.  At approximately age 10, breasts begin to develop.  At approximately age 11, pubic hair begins to appear, and a weight spurt begins.  At approximately age 11 1/2, the height spurt reaches its peak. At approximately age 12, females generally reach the peak of their organ growth and muscle development, and their hips become noticeably wider.  At approximately age 12 ½, girls experience menarche, which is their first menstrual period.  At approximately age 13, girls have their first ovulation.  At approximately age 14, their voice lowers.  At approximately age 15, they develop their final pubic hair pattern.  At approximately age 16, they have full breast growth.  At approximately age 9 1/2, boys’ testes increase production of testosterone.  At approximately age 10, their testes and scrotum grow larger.  At approximately age 11 1/2, boys’ pubic hair begins to grow.  At approximately age 12, the penis begins to grow.  At approximately age 12 ½, boys experience a weight spurt and their first ejaculation.  At approximately age 13, boys have their peak height spurt.  At approximately age 14, boys experience peak muscle and organ growth, and their shoulders become noticeably broader.  At approximately age 15, their voices lower, and facial hair becomes visible.  At approximately age 18, boys show the final pubic hair pattern.  Please note that these average ages are rough approximations, with many perfectly healthy adolescents as much as three years ahead of or behind these ages.  Also,  estrogen and testosterone influence sexual characteristics, including the potential for reproduction. Charted in this table are the increases in hormones produced by the gonads (sex glands). Adrenal glands produce some of both kinds of hormones (not shown).

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

 A group of adolescent girls smiling at the camera

Given the evidence that body weight influences the age of puberty, body size differences between various ethnic groups within a society should predict differences in age of menarche. Does the research evidence support this assumption?

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

As you have seen, girls tend to mature earlier than boys. In general, most individual girls who mature later than their peers do not seem too bothered by their late blooming. They seem to benefit from the extra time to adjust to the developments of puberty. They are more likely to have the emotional maturity to handle their bodies’ changes.

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

A group of adolescents smiling at the camera

Research results on the effects on early or late puberty on boys has been somewhat varied. While Brooks‐Gunn argues in the video on the previous screen that current research reveals that the effects of early and late puberty on boys are relatively minimal to those on girls, the Berkeley Growth Study (1941) found that late‐maturing boys experience the most negative effects of all with the timing of puberty. This research found late‐maturing boys to be less dominant, less popular, and more likely to feel inadequate as compared to male peers who hit puberty at the more average age.

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

Two adolescents smiling at the camera

Question 1.1

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Correct! The hormonal signal for the start of puberty begins in the hypothalamus. From there, it travels to the pituitary and then to the adrenals and gonads.
Sorry. The hormonal signal for the start of puberty begins in the hypothalamus. From there, it travels to the pituitary and then to the adrenals and gonads.

Assessment: Check Your Understanding

A group of adolescent girls smiling at the camera

Question 1.2

3wkEEbd91/xd4k+iEr2c7hmb5bsZGuC2Mmif293NSl6GWTdZXFDI95k8yyDyr/BltQCAJVfO/0Z6J+a0tasi53KntHd+tI93OeQtj+VGlPEdjZKY4jxhgImgFoKx2PVvPmNsayIcfXs=
This statement is false. Girls mature earlier than boys by as much as two years.
This statement is false. Girls mature earlier than boys by as much as two years.

Assessment: Check Your Understanding

 A group of adolescents smiling at the camera

Question 1.3

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Correct! Today’s children in the U.S. usually enter into puberty between 8 ‐ 14 years of age.
Sorry. Today’s children in the U.S. usually enter into puberty between 8 ‐ 14 years of age.

Assessment: Check Your Understanding

 A group of adolescents talking outside of a building

Question 1.4

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Correct! In general, girls do not seem to suffer too much from late puberty and may, in fact, benefit from the extra time which allows them to mature cognitively and socially before their bodies begin to develop. In contradiction with historical research, current research on puberty in boys indicates that they experience minimal distress with late puberty.
Sorry. In general, girls do not seem to suffer too much from late puberty and may, in fact, benefit from the extra time which allows them to mature cognitively and socially before their bodies begin to develop. In contradiction with historical research, current research on puberty in boys indicates that they experience minimal distress with late puberty.

Assessment: Check Your Understanding

A group of adolescents smiling at the camera

Question 1.5

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Refer to the historical trend in the age of menarche, compare it to today’s age of menarche, and elaborate on how the more rapid weight gain in today’s females explains this change in the average age of menarche. Also, mention that within the population of pre‐teen girls, those who have the greatest body mass are likely to begin menstruating earlier than those who are thinner. One argument in favor of the weight hypothesis is 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.

Congratulations! You have completed this activity.Total Score: x out of x points (x%) You have received a provisional score for your essay answers, which have been submitted to your instructor.