CHAPTER-s

PUBERTY
NTRODUCTION

His
Puberty the
process of physical changes through which a
is the
Pu capable
able of sexual reproduction. It is initiated
ofsex child's body matures into
body
dult
ads: the
aries in aa girl, the testis in a boy. In by hormonal
ovaries signals from the brain to
response to the signals, the gonads produce
N
tk
Axmones hat Stimulate libido and the growth, function,
tha
and
A d skin. hair. breasts, and sex
transformation of the brain, bones
TRUASC
k .b l o d
organs. On average.
10-11 andend puberty around 15-17; boys begin around agesgirls begin
11-12 andpuberty around
end around 16-17.
ages
Thelandmark
majorlandr of puberty in females is
menarche, the onset of
aoes 12
12and 13. For males, it is the first menstruation,
which occurs
erwen ages ejaculation, which occurs on average at age
naherty which starts earlier than usual is known as
precocious puberty, and
usual is known as puberty
which starts later than delayed puberty.
Two of the most significant difierences between puberty in girls and puberty in boys are
at which it begins, and the major sex steroids involved, the
e
androgens
and the
estrogens.
Far boys, the androgen testosterone is the principal sex hormone; while the hormone that dominates
iemale development is an estrogen called estradiol. While estradiol promotes growth of the breasts
and uterus, it is also the principal hormone driving the pubertal growth spurt and epiphyseal
maturation and closure. The main steroid hormones, testosterone, estradiol, and progesterone as
well as prolactin play important physiological functions in puberty.

PUBERTY ONSET
between
Puberty is preceded by adrenarche, an increase of adrenal androgen production
ages 6-10. Adrenarche is accompanied by the early appearance of axillary
andpubic hair.
GnRH which precedes the rise in sex
The onset of puberty is associated with high
GnRH rise is Leptin. Leptin has in the
receptors
normones, LH and FSH. The cause of the increase with the onset of puberty.
which synthesizes GnRH. The levels of leptin
nypothalamus is completed. Individuals
who are deticient in
levels when puberty
and then decline to adult hormone produced by
fat cell that targets hypothalamus
tail to initiate puberty (Leptin is a
pun
to regular body weight by inhibiting hunger)

PUBERTY CHANGEs IN MALES the first physical

is
manitestation of
testicular enlargement atter the onset
SZe and virility: In boys, size about 6 years
maximal adult
size reaches ofthe
breadth of shatt of
the shaft ot
pube enoth the breadth
then the
f (gonadarche). Testicular enlarged, the length and and then
also start to enlarge to
will also
puberty. testicles have
After the testicles enag cavernosa will
nora cavernosa

penis and
corpora ormones andand to
to
produce hormones
the penis will ase and the glans functions: to
increas testis have
two primary ible for
which is responsible
most of the
for mos
adult PrOportions.
proppo The testosterone,

cells produce
uce sperm. The
The Le
Leydig
perm.
male pubertal changes.
 164 Physiology- Controllingand Coordinatings
ating Systeme
Male musculature and body shape: By the end of puberty, adult men have heavieri
eavier bones and
nearly twice as much skeletal muscle. Some ofthe bone growth (¢.g. shoulder width a n d
is greater, resulting in noticeably different male and female skeletal shapes. This muscle d Ja)
mainly during the later stages of puberty. and muscle growth can continue even after h p
er boys are
biologically adult.
Erections: The penis can regularly get erect during sleep and men or boys often
wake un
an erection. Once a
boy reaches his teenage years, erections occur much more with
.

frequently d.due
to puberty.
Foreskin retraction: During puberty, the membrane that bonds the inner surface of the
foreskin
with the glans disintegrates and releases the foreskin to separate from the glans. The
foreskin
then gradually becomes retractable.
Pubic hair: Pubic hair often appears on a boy shortly after the genitalia begin to
grow. The
pubic hairs are usually first visible at the dorsal (abdominal) base of the penis. The first few
hairs are described as stage 2. Stage 3 > reached within another 6-12 months, when
the hairs
are too many to count. the
Stage 4> pubic hairs densely fill the "pubic triangle." Stage 5
spread of pubic hair to the thighs and upward towards the navel.
Body and facial hair: In the years following the appearance of pubic hair, other areas of skin
may also develop androgenic hair. The usual sequence is: underarm (axillary) hair, perianal
hair, upper lip hair, periareolar hair, and the beard area. Facial hair is often present in late
adolescence. Facial hair will continue to get coarser, darker and thicker for another 2-4
years
after puberty. Some men do not develop full facial hair for up to 10 years after the completion
ofpuberty. est hair may appear during puberty or years after, though not all men develop it.
Voice change : Under
the influence of androgens, the voice box, or
larynx, grows in both
sexes. This growth is more prominent in boys, causing the male voice to deepen. Most of the
voice change happens during stage 3-4 of male
puberty around the time of peak growth. Adult
pitch attained at an average age of 15 years, although the voice may not fully settle until early
is
twenties. It usually precedes the development of facial hair
by several months to years.
PUBERTY CHANGES IN FEMALES
Breast development: The first
physical sign of puberty in girls is usually a firm, tender lump
under the center of
the areola of one or both breasts, occurring at about 10.5 years ot age. u
is referred to as thelarche. Within 6
to 12 months, the
and can be felt and seen swelling begun in both sides, softenc.
extending beyond the edges of the areolae. This is stage 3 or D
development. By another 12 months (stage 4), the breasts are
shape, with areolae and nipples approaching mature size a
forming a
disappears into the contour of the mature secondary
mound. In most young women, tnismound
breast (stage 5).
Pubic hair: Pubic hair is the second
visible change in puberty,
usually within a few mo
Theo
thelarche. It is referred to as
first few hairs are described as
pubarche. The pubic hairs are visible first along the ladla.
stage2. Stage 3 is usually reached within another 6-lZ nths,
 e System
Reproductive

165
numerous to count and appear on
re
h a i r s are t0o
the hacl
hen
the
fill the "pubic
the "pubic the pubic mound.
h a i r sd e n s e l y triangle." Stage 5 refers By stage 4, the pubic
irs
sometim
deabdominal upward towards the navel. In 15% pubic hair to the thighs and
dominal
Sa hair to
spread of
before breast development of girls, the
pears
begins. earliest pubic hair
.
agina, uterus, Ovaries: Perineal skin keratinizes
sg infection. The mucosal surface of the due to effect of estrogen increasing its
resistane to infection.

levelsofestrogen,
vagina also
becoming thicker and duller pink in changes in response to increasing
joesnithelium,
n
ginal epithelium, which in future
plays important
colour. Estrogen increase glycogen content
nns part in
(physiologic 1leukorrhea) are a normal effect of maintaining vaginal pH. Whitish
retions (physiologic
following thelarche, the uterus, ovaries, and the estrogen as well. In the two years
follicles in
uterine body to cervix ratio is 1:1; which increasesthetoovaries increase in size. Before
rty. uterine
puberty,
2:1 or 3:1 after
pubertal period. completion of
Menstruation and fertility: The first
menstrual bleeding is referred to as
tunically occurs about two years after menarche, and
thelarche. The average age of menarche
hetween 8 and 16. The time between menstrual is anytime
first two years after menarche. Ovulation
periods (menses) not always regular in the
is
may or may not accompany the
postmenarchal girls, about 80% of the cycles were early menses. In
50% in the third year and 10% in the sixth
in the anovulatory first year after menarche,
year.
Body shape, fat distribution, and body composition:
levels of estrogen, the lower half of the pelvis and the
During puberty, in response to rising
hips widen (providing a larger birth canal).
Fat tissue increases to a greater
percentage of the body composition especially in the breasts,
hips, buttocks, thighs, upper arms, and pubis. Progressive differences in fat distribution as well
as local skeletal
growth contribute to the typical female body shape by the end of puberty. On
average, at 10 years, girls have 6% more body fat than boys.

Body odour and acne: Rising levels of androgens can change the fatty acid composition
of perspiration, resulting in a more "adult" body odour. This often precedes thelarche and
pubarche by one or more years. Another androgen effect is increased secretion of oil (sebum)
from the skin. This change increases the susceptibility to acne, a skin condition that is
characteristic of puberty.
Other effects of hormonal changes: In girls, estradiol (the primary female sex hormone)
causes thickening of lips and oral mucosa as well as development of the vulva. In the vulva and
of the skin and the
growth of smooth muscle of
vagina, estradiol causes thickening (stratification)
cause pronounced growth of the labia minora and to a
the vagina. Typically estradiol will also
esser degree of the labia majora.
production of pheomelanin, resulting in
increased
Estradiol is also responsible for the
the lips, labia minora and sometimes labia majora. Estradiol
the characteristic red colour of the darker coloration of the areola
ovarian steroids also cause
along with other
 166
Physiology Controlling and CoordinatinggsSystema

(SOME FACTS ABOUT PUBERTY

Effects of early and late puberty onset

Several studies about puberty have examined the effects of an early or a late
onset of
puberty in males and females.
Girs: Early onset of puberty in girls can be psychologically damaging. The main reason f
effect is the issue of body image. Early-maturing girls usually look larger than girls who
not yet entered puberty. As a result they develop a negative view of their body image have
experiences lead to lower self-esteem, more depression and poorer body image in these These
aturing girls. Since physical and emotional differences set them apart from people inearly-thee
same age group, early-maturing girls develop relationships with older people which
their
may sometime
increase the social risks. Generally, later onset of puberty in girls produces
They exhibit positive behaviors in adolescence that continue to adulthood.
positive outcome
mes.

Boys: Early-maturing boys develop "more aggressive, law-breaking, and alcohol abusing"
behaviors, which result in anger towards parents and trouble in school and with the police
Early puberty also correlates with increased sexual activity and a higher instance of teenage
pregnancy, both of which can lead to depression and other psychosocial issues. However, early
puberty might also result in positive outcomes, such as popularity among peers, higher self.
esteem and confidence, as a result of physical
developments, such as taller height, developed
muscles and better athletic ability.
Late-maturing boys develop lower self-esteem and confidence and generally have
lower popularity among peers, due to their less-developed physiques. Also, they experience
problems with anxiety and depression and are more likely to be afraid of sex than other boys.
Age of onset of puberty: The age at which puberty begins varies between individuals.
Usually, it begins between 10 and 13 years of age. The age at which puberty begins is affected
by both genetic factors and by environmental factors such as race, nutritional state and social
circumstances. For example, the earliest average onset of
puberty is for African-American
girls and the latest average onset is for high altitude subsistence populations in Asia.
The average age at which the onset of
the 1840s. In every decade from 1840 to 1950
puberty occurs has dropped significantly since
there was a drop of four months in the average
age of menarche among Western European females. In
1945 to 1975 in Japan there was a
Japan the decline happened later: from
drop
of 11 months per decade.
Genetic influence and environmental
factors: The genetic association of
between mothers and timing is strongest
daughters. Early puberty onset may also be caused by certain
namely phthalates, which are used in many cosmetics, chemicals.
toys, and plastic food containers.
the first observed
environmental effects is that puberty occurs later in One o
altitudes. The most children raised higner
at
of others have been
important of the environmental influences is
clearly nutrition, but a numbe
identified, which affect the timing of female puberty and menarche thau
male puberty.
Hormones and steroids : There is
and chemicals
theoretical concern, that environmental hormon
may affect prenatal or
postnatal sexual development in humans. Large ts
amou
ReproductiveSystem
167
metabolized estrogens and progestogens from
i
of incompletely pharmaceutical products are
reted into the sewage systems of large cities, and are sometimes detectable in the
ex
uironment. Significant exposure of a child to hormones or other substances that activate
env

strOgen or androgen receptors could produce some or all of the changes of puberty.
Bisphenol A (BPA) is a chemical used to make plastics, baby bottles, water bottles.
sports equipment, medical devices, and as a coating in food and beverage cans. BPA affect the
nrOstate gland, mammary gland, and lead to early puberty in girls. BPA leaches out of plastic
of
into liquids and foods, and mimics the action of estrogen. BPA is more likely to leach out
plastic when its temperature is increased, as when one warms a baby bottle or warms up food
in the microwave. The highest estimated daily intakes of BPA occur in infants and children.

Nutritional influence :Nutritional factors are the strongest and most obvious environmental
factors affecting timing of puberty. Girls are sensitive to nutritional regulation because they
calories (beyond
must contribute all of the nutritional support to a growing foetus. Surplus
brain the availability
requirements) are reflected in the amount of body fat, which signals to the
of resources for initiation of puberty and fertility.
and increase
Increasedconsumption of animal protein, other changes in nutrition,
Lower protein intakes and
in childhood obesity have resulted in falling ages of puberty.
are associated with later onset and slower
higher dietary fibre intakes, as in vegetarian diets,
progression of female puberty.
aftecttiming of
of daily physical activity has also beenforshown
to
Exercise: The average level
in females. A level of exercise, whether
high athletic
or body image
puberty, especially
available for reproduction and slows puberty.
purposes, reduces energy calories
ncien