front of the pelvis and the ischial bones at the
back of the pelvis. The shaft is the length of the
penis that extends outward from the body, and
the glans is the end or head of the penis. The URE-
THRAexits the glans through an opening called the
urethral meatus. A loose fold of SKIN, the foreskin
(also called the prepuce), covers the glans at birth;
beginning around 8 years of age the foreskin
retracts from the glans when the penis is erect and
returns to drape the glans when the penis is flac-
cid. CIRCUMCISIONis a surgical OPERATIONto remove
the foreskin.
The interior penis contains three channels: the
corpus spongiosum runs along the underside of
the penis and houses the urethra; the two corpora
cavernosa run side-by-side along the top of the
penis and engorge with BLOOD to stiffen and
enlarge the penis during ERECTION. A wall of
fibrous tissue, the septum, separates and supports
the corpora cavernosa. The inside of each corpus
cavernosum is a honeycombed network of spaces
(called trabeculae) that fill with blood when the
penis is erect. The erect penis is capable of pene-
trating the woman’s VAGINAduring SEXUAL INTER-
COURSE, with sexual stimulation culminating in
ORGASMand EJACULATION.
HEALTH CONDITIONS THAT CAN AFFECT THE PENISBALANITIS CANCER OF THE PENIS
CHORDEE EPISPADIAS
ERECTILE DYSFUNCTION GENITAL HERPES
HUMAN PAPILLOMAVIRUS(HPV) HYPOSPADIAS
HYPOGONADISM KLINEFELTER’S SYNDROME
PARAPHIMOSIS PEYRONIE’S DISEASE
PHIMOSIS PRIAPISM
For further discussion of the penis within the
context of the structures and functions of repro-
duction and sexuality, please see the overview sec-
tion “The Reproductive System.”
See also OVARIES; SEXUAL DYSFUNCTION; SEXUAL
HEALTH.
perimenopause The period of time during
which a woman’s body transitions from FERTILITY
to MENOPAUSE. The length of perimenopause varies
widely though tends to be five to seven years.
Perimenopause begins with the changes in the
MENSTRUAL CYCLE that herald the approach of
menopause. These changes include irregular spac-
ing of menstrual periods (including skipped peri-
ods), unusually heavy or light menstrual flow,
light breakthrough bleeding (bleeding between
periods), and HOT FLASHES.Bleeding between periods may indicate
a health condition that requires treat-
ment. A doctor should evaluate break-
through bleeding to determine whether
it is normal.Because PREGNANCY is possible during peri-
menopause, as OVULATION may occur intermit-
tently, a woman who has two consecutive skipped
menstrual periods should have a pregnancy test.
Women typically experience a range of fluctuating
discomforts, notably hot flashes and sleep distur-
bances, during the menopausal transition.
Menopause is a point in time identified in retro-
spect as the complete absence of menstrual peri-
ods for 12 consecutive months.
See also DYSFUNCTIONAL UTERINE BLEEDING(DUB);
ENDOMETRIOSIS; MENSTRUATION; UTERINE FIBROIDS.Peyronie’s disease A condition in which a hard-
ened, fibrous plaque forms within the connective
tissue of the PENIS, causing a contracture that pulls
the penis into a curved position. Researchers do
not know what causes the plaque to form. Some
believe it represents an autoimmune response
(overreaction of the IMMUNE SYSTEM) and others
that it occurs as a reaction to traumatic injury.
Peyronie’s disease generally affects men age 50
and older. The contracture often causes PAIN, par-
ticularly when the penis is erect, and interferes
with or prevents SEXUAL INTERCOURSE.
The doctor can usually diagnose Peyronie’s dis-
ease on physical examination of the penis. The
plaque is both visible and palpable. The doctor
may request an ULTRASOUNDof the penis, which
shows the extensiveness of the plaque. In about a
third of men who have Peyronie’s disease the
plaque softens and goes away on its own. In other
men the curvature progresses to a certain point
and then remains stable. It is important to evalu-
ate the potential risks compared to benefits for
proposed treatments, which include injecting the
plaque with a medication to dissolve the fibrous318 The Reproductive System