Encyclopedia of Health and Medicine

uterus 351
remove the uterus (HYSTERECTOMY). Surgery provides
permanent correction, though in some
women the damage to the pelvic structures may
later experience vaginal prolapse (sagging of the
vaginal walls).
See also AGING, REPRODUCTIVE AND SEXUAL
CHANGES THAT OCCUR WITH; CYSTOCELE; LIGAMENT; MUS-
CLE; PREGNANCY; RECTOCELE; SURGERY BENEFIT AND RISK
ASSESSMENT.
uterus The hollow muscular organ that supports
and contains a PREGNANCY. Eight ligaments—one
anterior, one posterior, two round, two broad
(also called lateral), and two uterosacral—suspend
the pear-shaped uterus in the lower central
abdomen (pelvis), with the narrow end of the
uterus angled somewhat downward. This suspension
system allows the uterus, also called the
womb, to expand during pregnancy. The FALLOPIAN
TUBES join the uterus, one on each side of the wide
upper section called the fundus. The fundus angles
forward such that the uterus lies above the urinary
BLADDER.
The lower section of the uterus is the CERVIX, a
thick neck of muscular tissue that joins the uterus
with the VAGINA, the passage to the outside of the
body. In its nonpregnant state the uterus is about
three inches long and an inch thick; in PREGNANCY
the uterus expands to become nearly 10 times as
large as its nonpregnant size. Within four to six
weeks after CHILDBIRTH the uterus returns to nearly
its prepregnant size. The uterus has two layers of
structure: the outer myometrium and the inner
endometrium.
The surgical OPERATION to remove the uterus is
HYSTERECTOMY, which may be treatment for
ENDOMETRIAL CANCER, severe ENDOMETRIOSIS or UTER-
INE FIBROIDS, or DYSFUNCTIONAL UTERINE BLEEDING
(DUB).
The myometrium The myometrium is three
layers of strong, smooth (involuntary) MUSCLE. The
fibers of the innermost layer form two circular
patterns that emanate from the fallopian tubes
and extend to the cervix. The fibers of the middle
layer occur in random patterns that run lengthwise,
widthwise, and diagonally. These fibers primarily
support the network of BLOOD vessels that
nourish the myometrium. The outermost layer’s
fibers wrap diagonally (transversely) around the
uterus.
The myometrium grows during pregnancy to
accommodate the growing and enlarging FETUS.
Through mechanisms doctors do not fully understand,
the myometrium begins rhythmic and
increasingly intense waves of contractions, synchronized
across the three layers of muscle, that
ultimately result in childbirth. The contractions
stretch and thin (efface) the cervix and then push
the fetus through the cervix, into the vagina, and
out of the body.
The endometrium The inner structure of the
uterus is the endometrium, a membranous tissue
that contains abundant blood vessels and glands.
The endometrium responds to the monthly hormonal
cycle of estrogen and PROGESTERONE peaks
and troughs, thickening when blood levels of
ESTROGENS rise—a preparation for pregnancy—and
sloughing when estrogen drops and progesterone
rises—MENSTRUATION. When these hormonal cycles
cease with MENOPAUSE, the endometrium enters a
state of atrophy, in which it remains for the rest of
the woman’s life.
HEALTH CONDITIONS THAT CAN AFFECT THE UTERUS
ADENOMYOSIS
DYSFUNCTIONAL UTERINE BLEEDING (DUB)
ENDOMETRIAL CANCER
ENDOMETRIOSIS
PREGNANCY
ENDOMETRIAL HYPERPLASIA
PELVIC INFLAMMATORY DISEASE (PID)
UTERINE FIBROIDS
For further discussion of the uterus within the
context of the structures and functions of reproduction
and sexuality, please see the overview section
“The Reproductive System.”
See also HYSTEROSCOPY; OVARIES; SEXUAL HEALTH.