Encyclopedia of Health and Medicine

278 The Reproductive System
thesia), then makes the incision. After delivery of
the baby and the PLACENTA, the obstetrician sutures
(stitches) the incision closed.
Though once commonplace as a routine measure
to prevent tearing of the vagina and surrounding
tissues, episiotomy is now a procedure most
obstetricians perform only when it appears that a
natural tear will penetrate into the muscles of the
perineum or RECTUM. The prevailing belief supporting
preventive episiotomy had been that the
clean cut of a surgical incision healed more rapidly
and with fewer complications than the often
jagged wound that occurred with a natural tear
(also called a laceration). However, numerous
studies have failed to support this premise, and
the American College of Obstetricians and Gynecologists
(ACOG) now advises against routine episiotomy.
Most episiotomies heal in four to six weeks
though some women experience discomfort or PAIN
for up to several months, especially with SEXUAL
INTERCOURSE. Typically the obstetrician uses sutures
the body absorbs as the incision heals. Risks of episiotomy
include excessive bleeding, INFECTION, and
weakening of the muscles of the pelvic floor that
may result in URINARY INCONTINENCE, FECAL INCONTI-
NENCE, and painful sexual intercourse. Many practitioners
who provide care for women during
PREGNANCY and childbirth advocate prenatal efforts,
such as perineal massage to increase tissue elasticity
and KEGEL EXERCISES to strengthen and tone the
pelvic muscles; perineal massage during labor may
also reduce the risk for natural tears and thus lower
the likelihood for episiotomy.
See also CESAREAN SECTION; PRENATAL CARE; SUR-
GERY BENEFIT AND RISK ASSESSMENT.
erection The enlarged and hardened PENIS. Erections
begin in the male fetus before birth and continue
throughout life. An erection is necessary for
SEXUAL INTERCOURSE and in an adult man usually
occurs as a result of sexual arousal. Erections also
occur spontaneously during sleep, usually during
rapid eye movement (REM) sleep. A man typically
has up to a half dozen nocturnal erections each
night. Doctors do not know what causes nocturnal
erections though believe they are a consequence
of electrical activity in the BRAIN, not of sexual
stimulation.
An erection during sexual arousal occurs as a
result of interactions between the thoughts and
physical stimulation of the penis. The sequence of
interactions triggers the release of nitric acid,
acetylcholine, EPINEPHRINE, and other neurotransmitters
(biochemicals that conduct NERVE
impulses). These substances cause the smooth
MUSCLE tissue supporting the corpora cavernosa,
the two tubelike channels along the top of the
penis, to relax. BLOOD flows into the corpora cavernosa.
Some of the layers of tissue within the
penis contract to help hold the blood within the
corpora cavernosa, and valves in the veins that
normally carry blood from the penis close. These
events cause the size of the penis to increase in
length and circumference.
An erection may come to fullness within a few
seconds to several minutes, depending on numerous
factors such as the man’s age and lasts generally
until EJACULATION. Some men can sustain an
extended erection during sexual activity. Nearly as
quickly as the tissues of the penis release nitric
acid, they also release the enzyme phosphodiesterase
(PDE), which counters the actions of
nitric acid and other neurotransmitters to allow
blood to flow out of the penis. This action gains
momentum after ejaculation or other culmination
of sexual activity, serving to reverse the actions of
these neurotransmitters. The penis again goes
limp (becomes flaccid).
See also CONTRACEPTION; ERECTILE DYSFUNCTION;
FERTILITY; MASTURBATION; NEUROTRANSMITTER; PARAPHI-
MOSIS; PHIMOSIS; PRIAPISM; SEXUAL HEALTH; VEIN.
erectile dysfunction The reduced ability or inability
for a man’s PENIS to become erect or sustain an
erection adequate for SEXUAL INTERCOURSE. Erectile
dysfunction, sometimes called impotence, may
occur as a physiologic condition, psychologic or
emotional condition, or combination. Most commonly,
however, all of these factors contribute to the
condition. About 25 million men in the United
States have chronic (long-term) erectile dysfunction.
Physiologic causes of erectile dysfunction
include
• NERVE damage that occurs as a complication of
PROSTATECTOMY (surgery to remove the PROSTATE
GLAND)