Encyclopedia of Health and Medicine

etrograde ejaculation 335
Puberty begins with hormonal changes the
HYPOTHALAMUS and the PITUITARY GLAND initiate that
stimulate the gonads (ovaries in women and testicles
in men) to begin producing gonadotropins
(sex hormones)—ESTROGENS and 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 illness
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 chromosomes,
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 HAIR under 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 specific.
Puberty in Girls
BREAST buds, 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 CYCLE is regular and predictable.
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 competition,
which tends to cause later menarche. Both
are within the range of normal.
Puberty in Boys
Enlargement of the SCROTUM and 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 producing
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 concludes
in boys when the genitalia reach adult proportions,
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 precocious
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 stimulates
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 SEMEN enters the BLADDER instead of ejecting
from the PENIS during EJACULATION. Semen and
URINE share the URETHRA for 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 man