Bma Illustrated Medical Dictionary

olecranonIn the arm, the bony projec-

tion at the upper end of the ulnathat

forms the point of the elbow.

olfactory nerveThe first cranial nerve,

which conveys sensations of smell as

nerve impulses from the nose to the

brain. Each of the 2 olfactory nerves has

receptors in the mucous membrane lin-

ing the nasal cavity. These receptors

detect smells and send signals along

nerve fibres, which pass through tiny

holes in the roof of the nasal cavity and

combine to form the olfactory bulbs.

From here, nerve fibres come together

to form the olfactory nerve, leading to

the olfactory centre in the brain. Sense

of smell may be lost or impaired due to

damage to the olfactory nerves, usually

as a result of head injury.

oligo-A prefix meaning few, scanty or

little, as in oligospermia(too few sperm

in the semen).

oligodendrogliomaA rare and slow-

growing type of primary brain tumour

mainly affecting young or middle-aged

adults. Surgical removal of the tumour

can, in some cases, lead to a total cure.

oligohydramniosA rare condition in

pregnancy in which there is insufficient

amniotic fluid surrounding the fetus in

the uterus.

oligospermiaA temporary or perma-

nent deficiency in the number of sperm

in the semen. Oligospermia is a major

Oestrogen drugs are often used together
with progestogen drugs.
Oestrogens suppress the production
of gonadotrophin hormones, which
stimulate cell activity in the ovaries.
High doses are used in postcoital con-
traception to prevent conception (see
contraception, emergency). They are also
used to treat, or sometimes prevent,
menopausal symptoms and disorders.
Oestrogens may be used to treat certain
forms of infertility, female hypogonadism,
abnormal menstrual bleeding, prostatic
cancer (see prostate, cancer of), and cer-
tain types of breast cancer.
Oestrogens may cause breast tender-
ness and enlargement, bloating, weight
gain, nausea, reduced sex drive, depres-
sion, migraine, and bleeding between
periods. Side effects often subside after
2 or 3 months. The drugs can increase
the risk of abnormal blood clotting and
susceptibility to high blood pressure (see
hypertension). Oestrogen drugs should
not be taken in pregnancy as they may
adversely affect the fetus.
oestrogen hormonesA group of hor-
monesthat are essential for normal
female sexual development and healthy
functioning of the reproductive system.
In women, they are produced mainly in
the ovariesand also in the placentain
pregnancy. Small amounts are pro-
duced in the adrenal glandsin both
men and women, but oestrogens have
no known specific function in men. When
levels are low, oestrogen hormones can
be replaced with oestrogen drugs.
oestroneSee estrone.
ofloxacin A quinoloneantibiotic used to
treat skin, soft tissue, and lower respira-
tory tractand urinary tract infections. It is
usually taken in tablet form to treat infec-
tions that have not responded to other
drugs but is also given by intravenous
infusion for severe systemicinfections.
Side effects may include nausea, vomit-
ing, diarrhoea, and abdominal pain.
oilsSee fats and oils.
ointmentA greasy preparation used as
a vehicle to apply drugs in dry skin con-
ditions such as eczemaor to protect or
lubricate the skin.
olanzapineAn antipsychotic drugused
for the treatment of schizophrenia.

OESTROGEN HORMONES OLIGOSPERMIA

O

Nasal

cavity

Olfactory Brain Olfactory nerve

bulb

Nerve

fibres of

olfactory

receptors

OLFACTORY NERVE