oat cell carcinoma A form of lung can-
cer, also known as small cell carcinoma.
obesityA condition in which excess fat
has accumulated in the body. A person
20 per cent above the recommended
weight for his or her height (see weight)
is obese rather than overweight.About
2 in 5 people in the UK are overweight
and a further 1 in 5 obese.
Obesity is usually caused by consuming
more food than is needed for energy.
Energy requirements are determined by
metabolic rate (see metabolism) and level
of physical activity. Family history is
sometimes a factor. Obesity is associated
with some hormonal disorders, but these
are not generally the cause.
Obesity increases the risk of hyper-
tension,stroke, and diabetes mellitustype
2.Coronary artery disease is more com-
mon, particularly in obese men under
- Obesity in men is also associated
with increased risk of cancer of the colon,
rectum, and prostate, and, in women, of
the breast, uterus, and cervix. Extra
weight may aggravate osteoarthritis.
The first line of treatment is a slimming
diet (see weight reduction) plus regular
exercise. Drugs such as appetite sup-
pressants are rarely used due to their
side effects. Wiring of the jaws, stapling
of the stomach, and intestinal bypass
operations are attempted only if obesity
is endangering a person’s health.
obsessive–compulsive disorderA psy-
chiatriccondition in which a person is
dogged by persistent ideas (obsessions)
that lead to repetitive, ritualized acts
(compulsions). Obsessions are com-
monly based on fears about security or
becoming infected. In obsessional rum-
ination, there is constant brooding over
a word, phrase, or unanswerable prob-
lem. Compulsions may occur frequently
enough to disrupt work and social life.
The disorder is often accompanied by
depressionand anxiety. If severe, a per-
son may become housebound.
The disorder usually starts in adoles-
cence. Genetic factors, an obsessive
personality, or a tendency to neurotic
symptoms may contribute. Some types
of brain damage, especially in enceph-
alitis, can cause obsessional symptoms.
Many sufferers respond well to beha-
viour therapy, which may be combined
with antidepressant drugs, but symp-
toms may recur under stress.
obstetricsThe branch of medicine con-
cerned with pregnancyand antenatal
care,childbirth, and postnatal care. It is
also the study of the structure and func-
tion of the female reproductive system.
(See also gynaecology.)
obstructive airways diseaseSee pul-
monary disease, chronic obstructive.
occiputThe lower back part of the head,
where it merges with the neck.
occlusionBlockage of a passage, canal,
opening, or vessel in the body. This may
be due to disease (for example, a pul-
monary embolism) or medically induced.
Occlusion also describes eye-patching
for amblyopia, and the relationship
between the upper and lower teeth when
the jaw is shut. (See also malocclusion.)
occultHidden or obscure,such as occult
blood in a sample of faeces.
occult blood, faecalThe presence in
the faeces of blood that cannot be seen
by the naked eye, but can be detected
by chemical tests. Such tests are widely
used in screening for cancer of the colon
(see colon, cancer of). Faecal occult
blood may also be a sign of a gastroin-
testinal disorder such as oesophagitis,
gastritis, or stomach cancer; cancer of
the intestine (see intestine, cancer of);
rectal cancer (see rectum, cancer of);
diverticular disease; polypsin the colon;
ulcerative colitis; or irritation of the
stomach or intestine by drugs such as
aspirin. (See also rectal bleeding.)
occupational disease and injuryIll-
nesses, disorders, or injuries that result
from exposure to chemicals or dust, or
are due to physical, psychological, or bio-
logicalfactors in the workplace.
Pneumoconiosisis fibrosisof the lung
due to inhalation of industrial dusts,
such as coal. Asbestosisis associatedOAT CELL CARCINOMA OCCUPATIONAL DISEASE AND INJURY
O