I
autoclave
A piece
of apparatus that produces
steam at high pressure within a sealed
chamber; the heat of the water vapour
destroys microorganisms. Autoclaving is
used in hospitals for the
sterilization
of
surgical equipment.
autograft
Tissue that has been transplanted from
one part of an individual’s body to
another (see
grafting).
Autografting is
often used to treat severe burns.
autoimmune disorders
Any of a number of disorders caused by
a reaction of the body’s
immune system
against its own cells and tissues. Such
disease-producing processes, known as
hypersensitivity
reactions, are similar to
the reactions that occur in
allergy,
except
that in autoimmune disorders the hyper-
sensitivity response is to the body itself
rather than to an external substance.
CAUSES
The immune system normally distin-
guishes “self” from “nonself”. Some
lymphocytes
(a type of white blood cell)
are capable of reacting against self, but
these lymphocytes are generally suppres-
sed. Autoimmune disorders occur when
AUTOIMMUNE DISORDERS
Specific
(organs or cells affected)
• Addison’s disease (adrenal glands)
• Autoimmune haemolytic anaemia
(red blood cells)
• Autoimmune chronic active hepatitis (liver)
• Autoimmune infertility (sperm or ovary)
• Diabetes mellitus type 1 (pancreas)
• Goodpasture’ssyndrome (lung and kidney)
• Graves’ disease (thyroid gland)
• Hashimoto’s thyroiditis (thyroid gland)
• Idiopathic thrombocytopenia purpura
(platelets)
• Myasthenia gravis (muscle receptors)
• Pernicious anaemia (stomach lining)
• Vitiligo (melanocytes)
Nonspecific
• Behcet’s syndrome
• Rheumatoid arthritis
• Sjogren’s syndrome
• Systemic lupus erythematosus
AUTONOMIC NERVOUS SYSTEM
there is interruption of the normal con-
trol process, allowing such lymphocytes
to escape from suppression, or when
there is alteration in a particular body
tissue meaning that it is no longer rec-
ognized as self and is attacked.
Bacteria, viruses, and drugs may play
a role in initiating an autoimmune dis-
order in someone who already has a
genetic (inherited) predisposition, but
in most cases the trigger is unknown.
TYPES
Autoimmune processes can have various
results, such as the destruction of a par-
ticular type of cell or tissue, stimulation
of an organ into excessive growth, or
interference in an organ’s function.
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, auto-
immune activity is towards a tissue,
such as connective tissue, that is wide-
spread in the body. Examples of such
disorders are systemic
lupus erythemato-
sus
and
rheumatoid arthritis.
TREATMENT
Initial treatment for any autoimmune
disorder is to reduce the effects of the
disease by, for example, replacing hor-
mones, such as insulin, 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
for this purpose but may be combined
with other
immunosuppressant drugs.
autologous blood transfusion
See
blood transfusion, autologous.
automatism
A state in which behaviour is not
controlled by the conscious mind. An
individual carries out activities without
being aware of doing so, and later he or
she has no clear memory of what hap-
pened. Episodes of automatism start
abruptly and are usually no more than a
few minutes in duration.
Automatism is uncommon and may
be a symptom of
temporal lobe epilepsy
,
dissociative disorders
(psychological ill-
nesses in which a particular mental
function is lost), drug or
alcohol in-
toxication,
or
hypoglycaemia
(low blood
sugar levels).
autonomic nervous system
Also called the involuntary nervous sys-
tem, the part of the
nervous system
that
controls the involuntary activities of a
variety of body tissues, including blood
vessels, organs, and glands. The auto-
nomic nervous system consists of a
network of nerves divided into the
sympathetic and parasympathetic ner-
vous systems.
The two systems act in conjunction
and normally balance each other. How-
ever, during exercise or at times of
stress, the activity of the sympathetic
system
predominates,
while
during
sleep the parasympathetic system exerts
greater control.
SYMPATHETIC NERVOUS SYSTEM
The sympathetic nervous system com-
prises two chains of nerves that pass
from the spinal cord throughout the
body tissues. Into these tissues, the
nerve endings release the
neurotrans-
mitters
(chemical messengers)
adrenaline
(epinephrine) and
noradrenaline
(nor-
epinephrine). The sympathetic nervous
system also stimulates the release of
adrenaline from the adrenal glands.
In general, the actions of the sympa-
thetic nervous system heighten activity
in the body. This activity is known as
the
fight-or-flight response.
Among the
most important effects produced are
the acceleration and strengthening of
the heartbeat, widening of the airways,
widening of the blood vessels in mus-
cles and narrowing of those in the skin
and abdominal organs
(in order to
increase the blood flow through the
muscles), and the inducement of sweat-
ing. In addition, the activity of the
digestive system is decreased and the
pupils are dilated.
PARASYMPATHETIC NERVOUS SYSTEM
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 those of
adrenaline and noradrenaline.
The parasympathetic system is con-
cerned mainly with everyday functions
such as digestion and excretion.
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