OLIGURIA
OPERABLE
O
cause of
infertility,
especially when other
disorders of the sperm are also present.
Normally, there are more than 20 mil-
lion sperm per millilitre of semen. A low
sperm count can be due to various dis-
orders, including
orchitis,
undescended
testis (see
testis,
undescended), and,
infrequently, a
varicocele
(varicose vein
of the testis). Smoking, alcohol abuse,
stress, and some drugs may cause tem-
porary oligospermia. Treatment is for
the underlying cause. If the cause is
unknown,
gonadotrophin hormones
may
be prescribed. (See also
azoospermia.)
oliguria
The production of low quanti-
ties of
urine
in proportion to the volume
of fluid taken in. The condition may be
caused by excessive sweating; in some
cases, it is a sign of
kidney failure.
olive oil
An oil, obtained from the fruit
of the olive tree
OLEA EUROPAEA
,
that
may be used to soften earwax or to treat
cradle cap
in babies.
-oma
A suffix denoting a tumour, which
may be cancerous or noncancerous, as
in
lipoma
and
carcinoma
.
omentum
A double fold of fatty mem-
brane hanging in front of the intestines.
omeprazole
A drug that is used to treat
peptic ulcer,
reflux
oesophagitis,
and
Zollinger-Ellison syndrome.
Adverse ef-
fects include rashes, headache, nausea,
diarrhoea, and constipation.
omphalocele
An alternative name for
exomphalos.
onchocerciasis
A tropical disease, also
called river blindness, caused by the
worm
onchocerca volvulus.
The dis-
ease is a type of
filariasis
transmitted by
simulium flies. The worms' dead larvae
can lead to blindness if they cause an
allergic reaction in or near the eyes.
Treatment is with
anthelmintic drugs
.
oncogenes
Genes found in every cell that
control growth, repair, and replacement.
Abnormalities of oncogenes are known
to be a factor in the development of can-
cerous cells.
Mutations
in oncogenes,
resulting from damage by
carcinogens
,
can cause a cell to grow unrestrainedly
and infiltrate and destroy normal tissues
(see
cancer
). Factors known to cause
cancer include ultraviolet light, radioac-
tivity, tobacco, alcohol, asbestos, some
chemicals, and certain viruses.
oncology
The study of the causes, devel-
opment, characteristics, and treatment
of tumours, particularly cancers.
ondansetron
A
serotonin antagonist
drug
used to control nausea and vomiting
following an operation or induced by
radiotherapy
or
anticancer drugs.
It is
taken as tablets or suppositories, or given
by injection. Side effects may include
constipation, headache, and hiccups.
onychogryphosis
Abnormal thicken-
ing, hardening, and curving of the nails
that occurs mainly in elderly people.
Onychogryphosis may be associated
with
fungal infection
or poor circulation.
onycholysis
Separation of the nail from
its bed: a feature of many skin condi-
tions, including
psoriasis
and
dermatitis
.
oophorectomy
Removal of the
ovaries
,
usually to treat
ovarian cysts
or cancer
(see
ovary, cancer of
). A partial oophor-
ectomy may be performed to preserve
ovarian function in women under 40. In
a
hysterectomy
, both ovaries may be
removed if disease has spread from the
uterus, or to prevent ovarian cancer from
developing in the future. The ovaries
may be removed as part of the treat-
ment for
breast cancer
if growth of the
tumour depends on hormones produced
by the ovary. If both ovaries are removed
before the menopause,
hormone replace-
ment therapy (HRS)
may be needed.
-opathy
A suffix that denotes a disease
or disorder, as in
neuropathy
(a disor-
der of the peripheral nerves).
open heart surgery
Any operation on
the
heart
in which it is stopped tem-
porarily and its function taken over by a
mechanical pump. The main forms of
open heart surgery are correction of con-
genital heart defects (see
heart disease,
congenital
), surgery for narrowed or leaky
heart valves (see
heart-valve surgery
),
and
coronary artery bypass
surgery. Once
the pump is connected, the heart is
opened, and the defects repaired. Surgi-
cal hypothermia is used to keep the
heart cool and help prevent damage to
the heart muscle from lack of oxygen
(see
hypothermia, surgical
).
operable
A term applied to a condition
that is suitable for surgical treatment,
such as an accessible noncancerous
tumour. (See also
inoperable.)
414
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