AUTOANTIBODY
AVASCULAR NECROSIS
first diagnosed in childhood, that are
characterized by obsessive behaviour
and impaired communication and social
skills (see
autism; Asperger's syndrome).
autoantibody
An
antibody
that reacts
against
the
body's
own
cells
(see
autoimmune disorders
).
autoclave
An apparatus that produces
steam at high pressure within a sealed
chamber. Autoclaving is used in hos-
pitals for the sterilization of surgical
equipment (see
sterilization
).
autoimmune disorders
Any of a num-
ber of disorders caused by a reaction of
the
immune system
against the body's
own cells and tissues. Bacteria, viruses,
and drugs may play a role in initiating
an autoimmune disorder, but in most
cases the trigger is unknown.
Autoimmune disorders are classified
into organ-specific and non-organ-spe-
cific types. In organ-specific disorders,
the autoimmune process is directed
mainly against one organ. Examples
include
Hashimoto's thyroiditis
(thyroid
gland), pernicious
anaemia
(stomach),
Addison's disease
(adrenal glands), and
type 1
diabetes mellitus
(pancreas). In
non-organ-specific disorders, autoim-
mune activity is towards a tissue, such
as connective tissue, that is widespread
in the body. Examples of non-organ-
specific disorders are systemic
lupus
erythematosus
and
rheumatoid arthritis.
Initial treatment for any autoimmune
disorder is to reduce the effects of the
disease, for example by replacing hor-
mones that are not being produced. In
cases in which the disease is having
widespread effects, treatment is also
directed at diminishing the activity of
the immune system while maintaining
the body's ability to fight disease.
Corti-
costeroid drugs
are most commonly
used but may be combined with other
immunosuppressant drugs.
automatism
A state in which behaviour
is not controlled by the conscious mind.
The individual carries out activities
without being aware of doing so, and
later has no clear memory of what hap-
pened. Automatism is uncommon and
may be a symptom of
temporal lobe
epilepsy
,
dissociative disorders
, drug or
alcohol intoxication
, or
hypoglycaemia
.
autonomic nervous system
The part
of the
nervous system
that controls the
involuntary activities of a variety of
body tissues. The autonomic nervous
system is divided into the sympathetic
and parasympathetic nervous systems.
The sympathetic nervous system com-
prises 2 chains of nerves that pass from
the spinal cord throughout the body tis-
sues.
Into these tissues, the nerve
endings release the
neurotransmitters
adrenaline
(epinephrine) and
noradren-
aline
(norepinephrine). The system also
stimulates adrenaline release from the
adrenal glands. In general, the actions of
the sympathetic nervous system height-
en activity in the body, quickening the
heartbeat and breathing rate, widening
blood vessels, and inducing sweating.
The parasympathetic nervous system
is composed of a chain of nerves that
passes from the brain and another that
leaves the lower spinal cord. The nerves
are distributed to the same tissues that
are supplied by the sympathetic nerves.
The parasympathetic nerves release the
neurotransmitter
acetylcholine
, which has
the opposite effect to adrenaline and nor-
adrenaline. The parasympathetic system
is mainly concerned with everyday func-
tions such as digestion and excretion.
The 2 systems act in conjunction and
normally balance each other. During
exercise or at times of stress, the sym-
pathetic system predominates, however,
while during sleep the parasympathetic
system exerts more control.
autopsy
A postmortem examination of
the body, including the internal organs,
usually to determine cause of death.
autosome
Any chromosome that is not
a sex chromosome. Of the 23 pairs of
chrom osom es
in each human cell, 22
pairs are autosomes.
autosuggestion
Putting oneself into a
receptive hypnotic-like state as a means
of stimulating the body's ability to heal
itself. For example, in one method used
to control anxiety symptoms, people are
taught muscular relaxation (
biofeedback
)
techniques and learn to summon up
calming imagery or pleasant thoughts.
avascular necrosis
The death of cells
in body tissue caused by damage to
blood vessels supplying the area.
A
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