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What changes should girls and boys expect?

Your body goes through two periods of rapid growth in your lifetime. The first is from birth to age three. The second is during puberty. Puberty is also a time of rapid development in the reproductive systems of both boys and girls. The changes in the reproductive system, which result in sexual maturation, make it possible to carry out the main biological function of the human species-to reproduce.

Did You Know?

Vital organs like the heart and lungs keep us alive as individuals. Sexual organs let us survive as a species.

Sexual maturation involves two kinds of change. “Primary” changes directly involve the reproductive organs themselves, such as the testes and ovaries. As a result males begin producing sperm and females begin producing eggs.

In addition, there are some related changes, such as the growth of breasts in females and the growth of hair under the armpits (axillary hair) and around the sex organs (pubic hair) in both sexes. These secondary sexual characteristics are considered “secondary” because they do not directly involve the reproductive organs themselves. These characteristics are sexual because they indicate sexual maturity and distinguish male from female.

‘‘I think what is happening to me is so wonderful, and not only what can be seen on my body, but all that is taking place inside. I never discuss myself or any of these things with anybody; and that is why I have to talk to myself about them’’.

-Diary of a Young Girl

Anne Frank

Sexual Maturation among Girls

For girls, one of the most important experiences of puberty is the onset of menstruation, which is the flow of blood, or the shedding of the lining of the uterus, from the vagina once a month. Most girls have their first period, called menarche, between the ages of 11 and 13, but it may occur just as normally as early as age 9 or as late as 16 or 17.

Figure 3.1 The primary changes and secondary sexual characteristics that females develop during puberty.

During a menstrual period, which usually lasts several days, menstrual fluid flows from the lining of the uterus and out through the vagina. This fluid is made up of blood and discarded tissue from the uterine lining. Most women have a menstrual period every month, except when pregnant, from puberty until about the age of 50. These years are a woman's childbearing years. When an older woman no longer has menstrual periods and can no longer bear children, she is said to have reached menopause. This too is a normal stage of adult life.

Word Origin: Menarche Where does the word menarche come from? Go to a dictionary or other word reference book and write down your findings.

Most girls are taught to expect their first menstrual period, but occasionally a girl will have it without warning, and she may think she is sick. However, menstruation is a normal body function and not an illness. During her menstrual period a woman can do all her usual activities. Only some women experience discomfort during menstruation, as we will discuss later in this unit.

The ovaries increase a little in size during adolescence. No new eggs are formed during puberty. A girl is born with all the eggs she will ever produce. (This is different for boys, who don't produce sperm until puberty and then produce millions of new sperm cells every day.) The eggs stay protected in an immature state in the ovaries until puberty; then each month one of them matures and is released from an ovary.

What Do You Think?

If girls are biologically able to have children by age 13, should they start becoming mothers at this time? Why or why not?

During puberty, breast development usually starts to show when the area under each nipple buds or swells a little. The area may be uncomfortable to touch for a while. In the next stage, the breasts and areolae, the darker skin around the nipples, increase in size.

Like other types of growth at puberty, the rate of breast growth may vary, so that one breast may be, for a while, larger than the other one. Although usually temporary, some girls may worry about the difference. Even some adult women have breasts of different sizes, but typically this is noticeable only to themselves. Any size difference comes mainly from the amount of fat stored in breast tissue, not from the milk glands in the breast. Breast size has nothing to do with a woman's ability to nurse a baby. Small breasts and large breasts function in the same way.

Did You Know?

  • Your body is covered with 5 million hair follicles, of which about 15% are inactive-so you have about 4 million hairs on you at any given time!
  • Hair and nails are made out of the same thing-dead cells filled with keratin, a protein.

Growth of pubic hair in the area of the genitals (external sex organs) and on the lower part of the abdomen is also a visible event of puberty for girls. When pubic hair first grows, it is very fine and straight, and there is only a little of it. Gradually, the hair becomes coarser, curlier, darker, and it begins to spread. About the time that the pubic hair begins to reach the adult state, axillary hair appears under the arms.

You should remember that the ages marking the beginning and end of puberty changes may vary a lot among girls. Sometimes, these developments last a shorter period of time or a longer period. These time period variations are perfectly normal. Variations within the sequence of changes are also normal, so it is possible that a girl may have her menarche even before other changes occur. But the most common order of changes is as shown in Figure 3.2.

How do animals distinguish male from female? Give some examples and describe the distinguishing secondary sexual characteristics.

Activity 3-1: Changes in Girls during Puberty

Introduction

The changes you go through at puberty follow a general schedule. The various changes occur in a fairly predictable order and on a fairly predictable time schedule. There is, however, a fairly wide range of normal in terms of when these events begin to occur and when they are complete.

Materials

  • Activity Report

Procedure

Step 1 Look at Figure 3.2 shown below.

a. The ages at which changes take place are listed on the horizontal line at the bottom of the graph.

b. The bars each represent a different change or development during puberty.

c. The dark part of each bar indicates the ages at which the change typically takes place, and how long it generally takes for the change to occur.

d. However, it is perfectly normal for each change to begin or end earlier or later than the “average” time. The dotted section of each bar indicates this normal range for each event.

e. For example, breast development in girls usually starts around age 11 and is completed by age 15 (the dark part of the bar), but it can start as early as 8, or as late as 13, and be completed at 17 (the dotted parts of the bar).

f. Notice that the graph for height spurt is different. Like the other changes, the increase in height goes on over several years, but the rate of growth starts out slowly, then it speeds up, reaches its peak, and slows down again.

g. Notice also that the dark band for the onset of the first menstrual period, known as menarche, is very short, because menarche is a brief, onetime event. The dotted part of the bar is wide, because although the average age of this development is between 12 and 13, it can occur as early as 9, or as late as 16 and still be within the normal range.

Step 2 Use this graph to answer the questions on your Activity Report.

Figure 3.2 Changes in puberty for girls.

Sexual Maturation among Boys

The early signs of sexual maturation among boys are not as obvious as among girls. You may hardly notice the earliest change, such as enlargement of the testes, the organs where sperm cells are produced. Change in the scrotum, which contains the testes, is a little more evident as its skin becomes coarser. About a year after the testes start to grow, the penis, the male organ through which sperm is delivered and urination occurs, also begins to grow in length while the testes and scrotum continue to enlarge.

As the testes enlarge, the production of sperm cells begins. The production of sperm cells begins during puberty and will continue throughout the rest of a man's life. Sperm production is necessary for reproduction, because a sperm cell will combine with a woman's egg cell to create an embryo. Nutrient fluids and sperm make up semen. Semen is what comes out of the penis during ejaculation.

Figure 3.3 The primary changes and secondary sexual characteristics that males develop during puberty.

Boys find out that they are producing semen if they begin having “wet dreams,” or nocturnal emissions. These occur when semen is ejaculated from the penis during sleep. Boys usually begin having wet dreams around the age of 13 or 14. Some have them earlier, later, or not at all. All of these experiences are normal. Though a wet dream is pleasurable, some boys worry about it. They may think they are sick, or they may feel embarrassed. However, nocturnal emissions are perfectly normal, and many boys have them. A boy may also experience his first ejaculation during masturbation, when he stimulates his own penis.

What is the function of the scrotum?

What Do You Think?

Can you think of any reasons that hair growth varies among cultural groups? For example, Asians grow lighter and more sparse facial hair, while Mediterranean and Middle Eastern men tend to have darker and heavier beards.

Among the secondary sexual characteristics, the growth of pubic hair in boys usually occurs early in puberty but may start any time between the ages of 10 and 15. Pubic hair appears first at the base of the penis. Initially, the strands of hair are sparse and straight. Then they become darker and coarser. Pubic hair continues to grow and spread up to the abdomen until well past puberty.

About two years after the appearance of pubic hair, boys develop hair under the armpits. At about the same time, the first downy hairs appear on the upper lip. Later, this facial hair spreads to the cheeks and becomes coarser, forming a beard and mustache. Depending on inheritance, some boys will develop heavy beards while others may have less facial hair. The amount of chest hair also varies-some men have a lot and others almost none. Growth of chest hair is a late event in puberty.

Men generally have deeper voices than women do. Late in puberty, boys' voices deepen when the larynx (voice box) in the throat grows larger. We often call this enlargement an “Adam's apple.” Boys go through a period when their voices crack, going from low to high pitch in the middle of a sentence. While more obvious in boys, voice changes also occur to some degree in girls.

Similarly, some changes we associate with girls may also occur in boys, though to a lesser degree. For example, boys may have some breast tenderness around the nipple, as well as a temporary enlargement of the breasts. An overweight boy may especially look as if he has breasts. This breast growth is fairly common (about 2 out of 3 boys by age 14) and usually shrinks in a year or two. If not, a doctor can treat this condition for reasons of appearance.

What Do You Think?

Why do we talk more about (and have a term for) a girl's first menstruation (menarche) than a boy's first ejaculation? Are they similar or different experiences?

As with girls, you should remember that the ages marking the beginning and end of puberty changes might vary a great deal between one boy and another. Sometimes, these developments last a shorter period of time or a longer period. These time-period variations are perfectly normal. Other variations within the sequence of changes are also normal; for example, the penis may start growing before pubic hair does.

Activity 3-2: Changes in Boys during Puberty

Introduction

The changes you go through at puberty follow a general schedule. The various changes occur in a fairly predictable order and on a fairly predictable time schedule. There is, however, a fairly wide range of normal in terms of when these events begin to occur and when they are complete.

Materials

  • Activity Report

Procedure

Step 1 Look at Figure 3.4 shown below.

a. The ages at which changes take place are listed on the horizontal line at the bottom of the graph.

b. The bars each represent a different change or development during puberty.

c. The dark part of each bar indicates the ages at which the change typically takes place and how long it generally takes for the change to occur.

d. However, it is perfectly normal for each change to begin or end earlier or later than the “average” time. The dotted section of each bar indicates this normal range for each event.

e. For example, development of the testes in boys usually starts around age 12 and continues through age 15 (the dark part of the bar), but it can start as early as 9 or as late as 15 and be completed at 17 (the dotted parts of the bar).

f. Notice that the graph for height spurt is different. Like the other changes, the increase in height goes on over several years, but the rate of growth starts out slowly, then it speeds up, reaches its peak, and slows down again.

Step 2 Use this graph to answer the questions on your Activity Report.

Figure 3.4 Changes in puberty for boys.

Activity 3-3: Knowing about Each Other

Introduction

Many changes take place during puberty. Some may be easy for you to accept or get used to. Others may take time to adjust to. How you feel about the changes of puberty varies from person to person. You may be very conscious of the changes that are going on in your own body but less aware of the changes going on in the opposite sex. It is important to realize that everyone has to deal with changes at puberty. Earlier in this section you learned about the changes that girls and boys go through. Now it is time to talk about how you feel about those changes and to think about how members of the opposite sex might be feeling about the changes that they have to face.

Materials

  • Activity Report

Procedure

Step 1 In the space provided on your Activity Report, write down five things that you think are the hardest things for someone of your sex to accept or feel comfortable with during sexual maturation.

Step 2 Then do the same thing for the opposite sex.

Step 3 Next, your teacher will divide the class into groups by gender. Compare the list that you have made with the other lists in your group. Have a member of the group keep a tally of how many times an item is mentioned. Then make a group list of the five most commonly mentioned items for boys and the top five items mentioned for girls.

Step 4 Select a representative from your group to read your group list to the class, or write it on the board, as directed by your teacher.

Step 5 As a class, compare the lists from all groups. First look at the lists for what boys might find difficult. Were the girls able to predict what changes the boys might find hardest? If not, have the girls explain why they thought a particular change might be hard for the boys, and have the boys respond to why this change is not particularly hard. If boys felt that a change would be hard for the girls but the girls did not identify it, have the boys explain why they see that change as difficult.

Step 6 Then reverse the process, and look at the lists for what girls might find difficult to deal with. Were the boys able to predict what changes might be hardest for the girls? If not, have the boys explain why they thought a particular change might be hard for the girls, and have the girls respond to why this change is not particularly hard. If the girls felt that a change would be hard for the boys but the boys did not identify it, have the girls explain why they see that change as difficult.

Factors Influencing Puberty

Hormones, discussed in the next section, bring about the changes of puberty. A number of factors influence these hormones and the timing of their release. All human growth and development, in fact everything that happens to living organisms, result from the interaction of two factors-heredity and environment.

Did You Know?

Hippocrates, an ancient Greek physician, thought colder climates caused puberty to start later. Weather does affect growth as discussed on this page, but not the way Hippocrates thought.

Heredity is the transmission of biological characteristics from parent to child. The agents of heredity are genes, which contain all the instructions about how the body is to develop and function. Every species has its own schedule of reproductive maturation. For humans, sexual maturation occurs during puberty. But genetic and environmental diversity ensures that each of us is unique-each of us develops in a predictable way, but not on a precise or identical schedule.

Height increases twice as fast in the spring and weight increases four times as fast in the fall. But the time of the onset of puberty remains somewhat unpredictable.

Genes pass along a tendency to develop at a certain rate. For example, girls unrelated to one another reach menarche (their first menstrual period) at ages differing on average by 19 months. Sisters, who inherit some of the same genes from their parents, begin menstruating within 10 months of reaching the same age. Identical twins, sharing exactly the same inheritance, start menstruating within an average of 3 months of each other.

Environment
Physical Social
air friends
food family
sun community

Figure 3.5 Elements of our physical and social environments.

Environment refers to everything around us, or the world in which we live. It includes the physical environment-the air we breathe, the food we eat, the sun that shines on us, and all else we come into contact with, whether or not we are aware of it. And it includes the social environment, the people with whom we interact. These people include our family and friends, the people in our school, community, and nation, and the world as a whole. This social environment is no less important to our development than the physical environment.

Environmental Influences on Puberty

Heredity makes it more likely you will look and sometimes even act a certain way, and its influence is difficult to control. Your environment, however, is changeable, although not always within your control. Your body's growth and development is very sensitive to your environment, especially to sources of nutrition and physical and emotional health. For example, if a young girl is undernourished or ill, her body will dedicate its food and energy to staying alive. Girls who live in places with inadequate or unpredictable food supplies tend to enter puberty later than usual. This makes sense since a woman's body should have a mechanism that protects her from conceiving (getting pregnant) when her body cannot physically sustain, or feed and care for, an infant.

What Do You Think?

How can you best evaluate and control your environment? Give an example of one element in your environment you can and want to change.

Numerous studies show a direct connection between nutrition and health and normal growth and development during childhood and puberty. Children living in extreme situations, where food and health care are scarce, may not grow as much or at the same rate as better nourished and cared for children. For these and other reasons, the rate of maturation in different environments varies. For example, girls in Cuba reach menarche about six years sooner than girls in the African country of Rwanda.

What Do You Think?

With medical advances available today, it is possible to medically treat children who do not enter puberty at the average age. Should we treat children who have not yet entered puberty at the average age, or wait for nature to take its course? Why or why not? How long should we wait?

Figure 3.6 Age of first menstrual period.

Another factor that can affect when an individual girl begins to menstruate is physical activity. For instance, girls who are very athletic tend to begin menstruating later than girls who are less active do. Women who engage in very strenuous exercise, such as marathon runners, may stop having menstrual periods for a while. The ratio, or percentage, of fat to body mass may influence the control of menstruation by the nervous system. Since exercise burns off fat, high levels of certain activities will influence the usual pattern of development at puberty.

Finally, emotional factors (part of your social environment) can also affect growth. Children from extremely deprived situations, growing up in homes where they do not receive love from those who care for them, do not grow at the same rate as other children. When these children are placed in an environment where they receive love and affection, their growth returns to average levels.

Did You Know?

One hundred years ago, in northern Europe, girls began to menstruate at about age 17. Now they usually reach menarche at about 12.8 years. This trend has leveled off, with girls now reaching menarche at about the same age as their mothers. The earlier maturation is due to better nutrition and health care.

A dramatic example of how social environment can affect growth occurred in a British orphanage right after the Second World War. Though food was scarce, the children received extra food and initially grew faster than those outside of the orphanage. Then a very harsh director took charge of the orphanage. She was very hard on the children and often punished them at mealtime. As a result, the growth rate of the children slowed, although they continued to receive the extra food. The only children who continued to grow at a higher rate were those to whom the director gave care and paid attention.

According to the Did You Know? on this page, the age of menarche has come down significantly in the last 100 years. Based on what you know about factors influencing puberty, what might explain this trend? This trend has stopped at about age 12.8 years. How might you explain why the trend has not continued?

Activity 3-4: Factors Influencing Puberty

Introduction

Many factors influence your growth and development. Some of these factors are within your control and others are not. In this activity you identify many of the factors that contribute to growth and development during puberty and decide which ones you can influence.

Materials

  • One Activity Report per group

Procedure

Step 1 Your teacher will divide you into groups.

Step 2 With your group, look over the Activity Report and decide which of the factors you have little or no control over and those you have some or a great deal of control over. Refer back to the text if you need to review the terms. Put them in the proper categories as indicated on your Activity Report. There may be some factors that you think actually fit in both categories. In that case you may put the factor in both charts but must explain your reasoning.

Step 3 After you have filled out the charts and answered the questions, select a member of your group to read your final paragraph aloud to the class.

Step 4 Compare your answers, and see if you can agree as a class on how to maximize your chances for healthy development.

‘‘Hormones thump hearts, tremble hands, fill you with butterflies of fear: They make you grow. They make you sleep. They wake you up again the next morning. Hormones shape embryos into boys and girls, and boys and girls into men and women’’.

-The Body Book

Sara Stein

Are you ready for all the changes that puberty will bring to you? What changes of puberty do you think will be the easiest and hardest to deal with for you? Why? What are the changes of puberty that you are actually the most excited about? What do you look forward to about growing up and changing?

Review Questions

  1. What is the difference between a primary and a secondary sexual characteristic?
  2. Give two primary changes for boys and two primary changes for girls.
  3. Give two secondary changes for boys and two secondary changes for girls.
  4. What are the major parts of the female reproductive system?
  5. What are some of the reasons a female might have irregular menstrual periods?
  6. Name three factors affecting puberty you can control and three factors you cannot control.

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