OOGENESIS
h y p e r l i p i d a e m i a s ) .
The
principal
side
effects are nausea and belching, but
these are uncommon.
o m e n tu m
A double fold of fatty membrane in the
abdomen (peritoneum) hanging in front
of the intestines that acts as a fat store.
o m e p ra z o le
A
p r o t o n p u m p i n h i b i t o r
drug used to treat
p e p t i c u l c e r ,
reflux
o e s o p h a g i t i s
(inflam-
mation of the gullet), and
Z o l l i n g e r -
E l l i s o n s y n d r o m e .
Possible adverse effects
include rashes, headache, nausea, diar-
rhoea, and constipation.
o m p h a lo c e le
An alternative name for
e x o m p h a l o s .
o n c h o c e rc ia s is
A
tropical
disease,
also
called
river
blindness, caused by infestation with
the worm O
n c h o c e r c a v o i v u i u s
. The dis-
ease, a type of
f i l a r i a s i s ,
affects millions
of people in some regions of Africa and
Central and South America.
CAUSES AND SYMPTOMS
Onchocerciasis is transmitted from per-
son to person by small, fiercely biting,
black sim ulium flies. These flies, w hich
breed in, and always remain near, fast-
running streams,
ingest microfilariae
(tiny worms)
and inject their larvae
into human skin, where they multiply
and spread around the body under the
skin (see the illustrated box).
The dead larvae can cause an allergic
reaction resulting in inflammation and
the formation of fibrous tissue. When
this occurs in the eye, the damage is
permanent
and
leads
to
blindness.
Symptoms
of the
condition
include
itchy, swollen patches; they usually arise
about a year after infestation.
TREATMENT AND PREVENTION
Treatment involves taking
a n t h e l m i n t i c
d r u g s ,
w hich quickly kill the microfilar-
iae. Such treatment needs to be repeated
annually because the adult worms are
not affected. Travellers to areas where
the disease
is prevalent should take
measures to discourage
i n s e c t b i t e s
.
o n c o g e n e s
Genes found in every cell of the body
that control growth, repair, and replace-
ment. Activation of an oncogene is a
factor in the development of cancerous
cells.
M u t a t i o n s
(structural changes) in
oncogenes, resulting from damage by
c a r c i n o g e n s ,
can cause a cell to grow
uncontrollably and infiltrate and destroy
normal
tissues
(see
c a n c e r ) .
Factors
known to encourage oncogene mutation
include ultraviolet light,
radioactivity,
tobacco smoke, alcohol, asbestos, and
some
chemicals.
In
addition,
some
viruses can activate oncogenes.
o n c o lo g y
The study of the causes, development,
characteristics, and treatment of
t u m o u r s
,
particularly
c a n c e r s
(malignant tumours).
Because there are many different types
of tumours, developing in virtually any
tissue in the body, oncology encom-
passes a wide range of experimental
techniques and investigative approach-
es. These include surveying the frequency
and distribution of tumours, testing new
treatments, investigating the biochemical
processes involved in tumour formation,
and studying abnormal genes that are
associated with tumours. Doctors spe-
cializing in the study and treatment of
cancer are known as oncologists.
o n d a n s e tro n
A
s e r o t o n i n a n t a g o n i s t
drug used to con-
trol the nausea and vomiting that occur
following an operation or that are indu-
ced by
r a d i o t h e r a p y
or
a n t i c a n c e r d r u g s
.
Ondansetron is taken in the form of
tablets or suppositories or is given by
injection. Side effects may include con-
stipation, headache, and hiccups.
o n y c h o g ry p h o s is
Abnormal thickening, hardening, and
curving of the nails that occurs mainly
in elderly people. It may be associated
w ith
f u n g a l i n f e c t i o n
or poor circulation,
or it may occur for no apparent reason.
Onychogryphosis
This thickening, hardening, and overgrowth of the
toenails occurs mainly in elderly people. It can also
affect the fingernails.
o n y c h o ly s is
Separation of the nail from its bed: a
feature of many skin conditions, includ-
ing
p s o r i a s i s
and
d e r m a t i t i s .
o o c y te
One of the cells that are found in the
o v a r y
that, after undergoing
m e i o s i s
(a
type of cell division), form ova (egg
cells; see
o v u m ) .
o o g e n e s is
The process by w hich mature ova (egg
cells; see
o v u m
) are produced in the
female’s ovary. At birth, a female has
her entire lifetim e’s
complement of
LIFE-CYCLE OF ONCHOCERCIASIS
The infestation is
spread by a fly that
ingests microfilariae
(tiny worms) from an
infested person. The
worms grow into
larvae inside the fly
and are deposited
in the skin of a new
human host when
the fly bites. In
the new host, the
larvae develop
into adults, which
produce micro-
filariae that migrate
around the body.
O
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