Aging Alters Reproductive Capacity
LEARNING OBJECTIVES
1.
Describe
the changes that occur at puberty.
3.
Explain
the changes that occur in the reproduc-
2.
Identify
the changes that occur during meno-
tive systems of older men.
pause.
A
t
birth,
humans
have
all
their
reproductive
organs,
but
these
organs are inactive because the
hypothalamic-pituitary-gonadal
axis does not yet function (see Chapter 9).
When we reach about 10 years of age, hor-
monal changes occur that cause us to start
p u -
b e r t y
and become sexually functional (
F ig u r e
1 6 . 1 9
). Females begin going through their re-
productive cycle and have their first menses,
called
m e n a r c h e
(me-NAR-ke), and males be-
gin producing sperm. Both genders develop secondary
functions
p u b e r ty
(PU-ber-te)
The time of life during
which the secondary
sex characteristics
begin to appear and
the capability for
sexual reproduction
is possible; usually
occurs between ages
10 and 17.
sex characteristics and are capable of repro-
duction.
The onset of puberty is marked by bursts
of LH and FSH secretion, each triggered by a
burst of GnRH. The cause of the GnRH burst
is not yet clear, but a role for the hormone
leptin is starting to unfold. Just before puberty,
leptin levels rise in proportion to adipose tis-
sue mass. Leptin may signal the hypothalamus
that long-term energy stores (triglycerides in
adipose tissue) are adequate for reproductive
to begin.
R e p r o d u c t i v e c a p a b i l i t i e s t h r o u g h o u t l i f e
F i g u r e 1 6 . 1 9
Childhood
Puberty
Young and
early
adulthood
(Birth to age 10)
(about ages 10-14)
(ages 15-40)
• The reproductive system is in
a juvenile state and does not
function.
• Neither male spermatogen-
esis nor female reproductive
cycles occur.
Bursts of GnRH from the hypothalamus stimulate
bursts of LH and FSH from the pituitary.
Secondary sex characteristics appear in both genders.
Female reproductive cycles begin and girls have their
Male spermatogenesis begins.
Both genders are capable of reproduction.
Both genders are fully capable of
reproduction.
Females capable of reproduction
Males capable of reproduction
502 CHAPTER 16
The Reproductive Systems
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