IN VIVO
IRIS
may be needed before a successful
pregnancy is achieved. Modifications of
the technique, such as
gamete intrafal-
lopian transfer
(GIFT), are simpler and
cheaper than the original method.
in vivo
Biological processes occurring
within the body. (See also
in vitro.)
involuntary movements
Uncontrolled
movements of the body. These move-
ments occur spontaneously and may be
slow and writhing (see
athetosis
)
;
rapid,
jerky, and random (see
chorea
)
;
or pre-
dictable, stereotyped, and affecting
1
part of the body, usually the face (see
tic
). They may be a feature of a disease
(for example,
Huntington's disease)
or a
side effect of certain drugs used to treat
psychiatric conditions.
iodine
An element essential for forma-
tion of the
thyroid hormones,
triiodothy-
ronine (T3) and thyroxine (T4), which
control the rate of
metabolism
(internal
chemistry) and growth and development.
Dietary shortage may lead to goitre or
hypothyroidism.
Deficiency in the new-
born can, if left untreated, lead to
cretinism.
Shortages are very rare in deve-
loped countries due to bread and table
salt being fortified with iodide or iodate.
Radioactive iodine is sometimes used
to reduce thyroid gland activity in cases
of thyrotoxicosis and in the treatment of
thyroid cancer. Iodine compounds are
used as antiseptics, in radiopaque con-
trast media in some X-ray procedures
(see
imaging techniques
)
,
and in some
cough remedies.
ion
A particle that carries an electrical
charge; positive ions are called cations
and negative ions are called anions.
Many vital body processes, such as the
transmission of nerve impulses, depend
on the movement of ions across cell
membranes. Sodium is the principal
cation in the fluid that bathes all cells
(extracellular fluid). It affects the flow of
water into and out of cells (see osmosis),
thereby influencing the concentration
of body fluids.
The acidity of blood and other body
fluids depends on the level of hydrogen
cations, which are produced by meta-
bolic processes. To prevent the fluids
from becoming too acidic, hydrogen
cations are neutralized by bicarbonate
anions in the extracellular fluid and
blood, and by phosphate anions inside
cells (see
acid-base balance
).
ionizer
A device that produces
ions
(electrically charged particles). Ionizers
that produce negative ions can be used
to
neutralize
positive
ions
in
the
atmosphere. Some people believe that
use of an ionizer reduces symptoms,
such as headaches and fatigue, that
may result from a build-up of positive
ions generated by electrical machines.
ipecacuanha
A drug (also called ipecac)
used to induce vomiting in the treatment
of types of
poisoning
.
ipratropium bromide
A
bronchodilator
drug
used to treat breathing difficulties.
IQ
The
abbreviation
for
intelligence
quotient, an age-related measure of
intelligence (see
intelligence tests
).
iridectomy
A procedure performed on
the eye to remove part of the
iris
.
The
most common type of iridectomy, known
as a "peripheral iridectomy", is usually
performed to treat acute
glaucoma. A
small opening is made, surgically or
with a laser, near the outer edge of the
iris to form a channel through which
aqueous humour
can drain,
iridocyclitis Inflammation of the
iris
and
ciliary body.
Iridocyclitis is more
usually known as "anterior
uveitis".
(See
also
eye
,
disorders of.)
iridotom y A surgical procedure per-
formed on the eye, in which an incision
is made in the
iris
using a knife or a
laser. (See also
iridectomy.)
iris The coloured part of the eye, made
up of a loose framework of transparent
collagen
and muscle fibres, that lies
behind the cornea and in front of the
Iris
IRIS
Pupil
318
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