I
Treatment is usually unnecessary for
any of these age spots, apart from solar
keratoses, which may eventually pro-
gress
to
skin
cancer.
Freezing
the
keratoses with liquid nitrogen or apply-
ing a cream containing a
cytotoxic drug
is
the usual treatment. They may also be
removed surgically under a local anaes-
thetic (see
anaesthesia, local).
ageusia
The lack of, or an impairment of, the
sense of taste (see
taste, loss of).
agglutination
See
clumping.
aggregation, platelet
The clumping
together
of
platelets
(small, sticky blood particles). Aggrega-
tion takes place when a blood vessel is
damaged. It is the first stage of
blood
clotting,
helping to plug injured vessels.
Inappropriate aggregation can have
adverse effects; if it occurs in an artery,
for example,
thrombosis
(a blood clot
forming in an undamaged blood vessel)
may result. Many drugs, including
aspi-
rin
and
clopidogrel,
help
to
reduce
platelet aggregation.
aggression
A general term for a wide variety of
acts of hostility. A number of factors,
including human evolutionary survival
strategies, are thought to be involved.
CAUSES
Androgen hormones
(male sex hormones)
seem to promote aggression, whereas
oestrogen hormones
(the female sex hor-
mones) may suppress it. Age is another
factor; aggression is more common in
teenagers and young adults, and some
people believe that it can result from
frustration or lack of affection as a
child. Sometimes a brain tumour or
head injury may lead to aggression.
Psychiatric conditions associated with
aggressive outbursts are
schizophrenia,
antisocial personality disorder, mania,
and
abuse of alcohol or amphetamine drugs.
Temporal
lobe
epilepsy,
hypoglycaemia,
and
confusion
due to physical illnesses
are other, less common, medical causes.
aging
Aging
is
the
physical
and
mental
changes that occur with the passing of
time and is associated with degenerative
changes in various organs and tissues,
such as loss of elasticity in the skin and
a progressive decline in organ function.
AGRAPHIA
Wear and tear causes cumulative dam-
age to the joints, and the muscles lose
bulk and strength. Wound healing and
resistance
to
infection
also
decline.
Gradual loss of nerve cells can lead to
reduced sensory acuity and difficulties
with learning and memory. However,
dementia
occurs in only a minority of
elderly people.
Heredity is an important determinant
of life expectancy, but physical degener-
ation may be accelerated by factors such
as smoking, excessive alcohol intake,
poor
diet,
and insufficient
exercise.
With advances in medical science, life
expectancy in the developed world has
risen dramatically over the last century.
agitation
Restlessness and the inability to keep
still, usually as a result of anxiety or
tension. People who are agitated engage
in aimless, repetitive behaviour, such as
pacing up and down or wringing their
hands, and they often start tasks and fail
to complete them.
Persistent agitation is seen in
anxiety
disorders,
especially if there is an under-
lying physical cause such as alcohol
withdrawal.
Depression
may
also
be
accompanied by agitation.
agnathia
A developmental defect in the fetus in
which the lower jaw is only partially
formed or may be entirely absent. (See
also
birth defects.)
agnosia
The
inability
to
recognize
objects,
despite adequate sensory information
about them reaching the brain via the
eyes or ears or through touch. In order
for an object to be recognized, the sen-
sory information it provides must be
interpreted, which involves the recall of
memorized information about similar
objects. Agnosia is caused by damage to
areas of the brain involved in interpre-
tative and recall functions. The most
common causes of this kind of damage
are
stroke
or
head injury.
TYPES
Agnosia is usually associated with just
one of the senses of vision, hearing, or
touch and is described as visual, audit-
ory, or tactile respectively. For example,
an object may be completely recogniz-
able by hearing and touch, but it cannot
be recognized by sight,
despite the
sense of vision being perfectly normal
(an example of visual agnosia).
Some people, after suffering a stroke
that damages the right cerebral hemi-
sphere, seem unaware of any disability
in the affected left limbs. This is called
anosognosia or sensory inattention.
OUTLOOK
There
is
no
specific
treatment
for
agnosia, but some of the lost interpreta-
tive ability may eventually return.
agonist
A term that means to have a stimulating
effect.
In
pharmacology,
an
agonist
drug, which is sometimes known as an
activator, is a drug that binds to a spe-
cific area on the surface of a cell (a
receptor
) and triggers or increases a par-
ticular activity in that cell.
agoraphobia
Fear of going into open spaces or public
places.
Agoraphobia
may
sometimes
overlap with
claustrophobia
(a fear of
enclosed spaces). Agoraphobic individ-
uals who do venture out may have a
panic attack,
further
restricting
their
activities, and may eventually be house-
bound. Treatment with
behaviour therapy
is often successful;
antidepressant drugs
may also help.
agranulocytosis
A potentially life-threatening disorder,
in which there is a severe acute lack of
neutrophils (white blood cells that seek
and destroy infective microorganisms).
This deficiency seriously weakens the
body’s defences against infection.
In agranulocytosis, the bone marrow
fails to produce adequate neutrophils.
This may be an adverse effect of a
drug such as
carbimazole
(used to treat
thyroid diseases) or an effect of some
drug treatments for cancer (see
chemo-
therapy).
Fever
and
mouth
ulcers
commonly occur.
Treatment
is
with
antibiotic drugs
,
which should be started immediately to
prevent the development of severe, and
potentially fatal, infections.
agraphia
Loss of or impaired ability to write, des-
pite normal functioning of the hand
and arm muscles. Agraphia can result
from damage to the parts of the
cere-
brum
(the main mass of the brain)
concerned with writing.
CAUSES
The ability to write depends on a com-
plex
sequence
of mental
processes,
including the selection of words and
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