Chapter 3 Puberty and Biological Foundations - The McGraw-Hill ...

From Penguin Dreams and Stranger Things by Berkeley Breathed. Copyright © 1985 by The Washington Post Company.
By permission of Little, Brown and Co., Inc. and International Creative Management, Inc.
Determinants of Puberty
Although we do not know precisely what initiates puberty, a number of
complex factors are likely involved. Puberty is accompanied by changes
in the endocrine system, weight, body fat, and leptin, but we don’t
know if these are a cause or a consequence of puberty (Dorn, 2004). As
discussed next, heredity is an important factor in puberty.
Heredity Puberty is not an environmental accident. Programmed
into the genes of every human being is the timing for the emergence of
puberty (Adair, 2001). Puberty does not take place at 2 or 3 years of age
and it does not occur in the twenties. In the future, molecular genetic
studies may identify specific genes that are linked to the onset and progression
of puberty. Nonetheless, as we will see later in our discussion
of puberty, which takes place between about 9 and 16 years of age for
most individuals, environmental factors can also influence its onset and
duration.
Hormones Behind the first whisker in boys and the widening of
hips in girls is a flood of hormones, powerful chemical substances secreted
by the endocrine glands and carried throughout the body by the
bloodstream. Two classes of hormones have significantly different concentrations
in males and females: androgens, the main class of male
sex hormones, and estrogens, the main class of female hormones.
Note that although these hormones function more strongly in one sex
or the other, they are produced by both males and females.
Testosterone is an androgen that plays an important role in male pubertal
development. Throughout puberty, rising testosterone levels are
associated with a number of physical changes in boys, including the development of
external genitals, an increase in height, and voice changes (Hiort, 2002). Testosterone
level in adolescent boys is also linked to sexual desire and activity (Cameron, 2004).
Estradiol is an estrogen that plays an important role in female pubertal development.
As estradiol levels rise, breast development, uterine development, and skeletal
changes occur. The identity of hormones that contribute to sexual desire and activity
in adolescent girls is less clear for girls than boys (Cameron, 2004). Both boys and girls
experience an increase in both hormones during puberty. In one study, testosterone
levels increased 18-fold in boys but only 2-fold in girls during puberty; estradiol levels
increased 8-fold in girls but only 2-fold in boys during puberty (Nottelman & others,
1987) (see figure 3.1).
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Testosterone (ng/dl)
Estradiol (pg/ml)
500
400
300
200
100
110
0
0 1 2 3 4 5
90
70
50
30
10
50
40
30
20
10
110
Puberty 67
0
0 1 2 3 4 5
0 1 2 3 4 5 0 1 2 3 4 5
Boys Girls
90
70
50
30
10
Pubertal stage
FIGURE 3.1 Hormone Levels by Sex and Pubertal Stage
for Testosterone and Estradiol. The five stages range from the
early beginning of puberty (stage 1) to the most advanced stage of
puberty (stage 5). Notice the significant increase in testosterone in
boys and the significant increase in estradiol in girls.
hormones Powerful chemicals secreted by the
endocrine glands and carried through the body
by the bloodstream.
androgens The main class of male sex
hormones.
estrogens The main class of female sex
hormones.