Puberty begins with hormonal changes the
HYPOTHALAMUSand the PITUITARY GLANDinitiate that
stimulate the gonads (ovaries in women and testi-
cles in men) to begin producing gonadotropins
(sex hormones)—ESTROGENSand ANDROGENS. The
PINEAL GLAND, which regulates the body’s circadian
rhythms, also appears to play a role. Researchers
do not know what triggers these changes. Because
external factors such as nutritional status and ill-
ness can influence the timing of puberty,
researchers suspect body mass (height and weight)
may somehow signal the endocrine system. CHRO-
MOSOMAL DISORDERS involving the sex chromo-
somes, such as TURNER’S SYNDROME, which affects
girls, and KLINEFELTER’S SYNDROME, which affects
boys, alter or prevent natural puberty.
In both sexes, the first indication of puberty is
the growth of HAIRunder the arms and around the
GENITALIA. At first the hair is light and fine; as
puberty progresses the hair darkens and thickens.
Hair on the legs also darkens and becomes more
dense. There is usually an accompanying growth
spurt, which in boys particularly may amount to
six inches or more of height within a year. Boys
begin to broaden at the shoulders and girls at the
hips during this surge of growth. The remaining
changes that occur with puberty are gender spe-
cific.
Puberty in GirlsBREASTbuds, firm bumps that form beneath the
nipples, mark the onset of estrogen-driven
changes occurring in the girl’s body. In most girls
breast budding occurs simultaneously with the
development of pubic and axillary hair though
one set of events may precede the other. Over the
course of one to three years the breasts continue
to grow and take form and the girl’s body takes on
a womanly appearance. Generally, about the time
the pattern of body hair becomes adult-like the
girl begins to menstruate, indicating her ovaries
are mature and functional. Puberty concludes in
girls when the MENSTRUAL CYCLEis regular and pre-
dictable. External factors that can influence the
start of MENSTRUATION(MENARCHE) include OBESITY,
which tends to cause earlier menarche, and
intense physical activity such as athletic competi-
tion, which tends to cause later menarche. Both
are within the range of normal.
Puberty in Boys
Enlargement of the SCROTUMand testicles marks the
onset of TESTOSTERONE-driven changes occurring in
the boy’s body. The boy’s voice lowers in register
and deepens. Growth continues at a rapid rate.
Over the course of one to three years the PENIS
thickens and elongates, and the testicles begin pro-
ducing SPERM. Sexually stimulated ERECTION and
NOCTURNAL EMISSION(“wet dreams”) are common.
Toward the conclusion of puberty hair on the arms
may also become darker, longer, and more dense,
and hair begins to grow on the chest. Puberty con-
cludes in boys when the genitalia reach adult pro-
portions, which occurs at age 15 to 19.Precocious Puberty
Occasionally disturbances of hormonal function
may result in early, or precocious, puberty, which
doctors define as the onset of puberty before age 8
in girls and age 9 in boys. Treatment for preco-
cious puberty depends on the underlying cause of
the hormonal disturbance when the doctor can
identify it; a common cause is pituitary ADENOMA
(noncancerous tumor in the pituitary gland).
Often the cause remains unknown (idiopathic
precocious puberty), in which case the doctor may
administer GONADOTROPIN-RELEASING HORMONE
(GNRH) to regulate the pituitary gland’s release of
LUTEINIZING HORMONE(LH), the hormone that stimu-
lates estrogen and testosterone. There are usually
no adverse effects of idiopathic precocious
puberty.
See also AGING, REPRODUCTIVE AND SEXUAL
CHANGES THAT OCCUR WITH; HYPOGONADISM.retrograde ejaculation A circumstance in which
a man’s SEMENenters the BLADDERinstead of eject-
ing from the PENISduring EJACULATION. Semen and
URINEshare the URETHRAfor their exit from a man’s
body. A tiny valve in the urethra at the neck of
the bladder ordinarily closes across the entry to
the bladder during ejaculation, directing the flow
of semen through the penis. When this valve does
not close, semen takes the path of least resistance
and enters the bladder during ejaculation. A man
may notice retrograde ejaculation as a “dry
ORGASM” in which very little discharge leaves the
penis with orgasm. Retrograde ejaculation does
not present any health concerns for the manretrograde ejaculation 335