I
acid-fast
A characteristic of particular bacteria
(especially those responsible for tuber-
culosis) that are resistant to the acids
used to dye specimens for microscopic
examination (see
staining).
acidosis
A disturbance of the body’s
acid-base
balance
in which there is an accumu-
lation of acid or loss of
alkali
(base).
There are two types of acidosis: meta-
bolic and respiratory.
CAUSES
In
metabolic
acidosis,
an
increased
amount of acid is produced by meta-
bolic processes. One form of metabolic
acidosis is ketoacidosis, which occurs in
uncontrolled
diabetes mellitus
and star-
vation. Metabolic acidosis may also be
caused by loss of bicarbonate (an alkali)
as a result of severe diarrhoea. In
kidney
failure,
there is insufficient excretion of
acid in the urine.
Respiratory
acidosis
occurs
when
breathing fails to remove enough car-
bon dioxide from the lungs. This causes
increased acidity of the blood because
the excess carbon dioxide remains in
the bloodstream, where it dissolves to
form carbonic acid. Impaired breathing
leading to respiratory acidosis may be
caused by chronic obstructive pulm-
onary disease (see
pulmonary disease,
chronic obstructive),
bronchial
asthma,
or
airway obstruction
.
acid reflux
The regurgitation of acidic fluid from
the stomach into the
oesophagus
(the
tube that connects the throat to the
stomach). Acid reflux is the result of
inefficiency of the muscular valve at the
lower end of the oesophagus.
Also known as
gastro-oesophageal
reflux disease (GORD), acid reflux may
inflame the oesophagus, resulting in
heartburn
(a burning pain in the chest)
due to
oesophagitis
(inflammation of
the oesophagus).
Mild acid reflux is common but is
not serious. It may occur during preg-
nancy
and
often
affects
overweight
people. Repeated episodes of discom-
fort may indicate a
hiatus hernia
(in
which part of the stomach protrudes
into the chest).
acne
A chronic skin disorder in which there
is inflammation of the
sebaceous glands
at the base of hair follicles in the skin.
ACOUSTIC NEUROMA
help to keep it under control. Over-the-
counter topical drug treatments such as
benzoyl peroxide or azelaic acid are
often effective. Prescribed topical
anti-
biotic drugs
or retinoic acid (a derivative
of
vitamin A)
are used to treat moderate
acne. Alternative treatment is with oral
antibiotics, often
tetracycline drugs.
In
very severe cases,
isotretinoin
may be
given under hospital supervision. In
all cases, exposure to ultraviolet light
(either natural or artificial) may also
be beneficial. However, it is important
not to burn the skin.
Acne improves slowly over time, and
it often clears up by the end of the
teenage years.
acoustic nerve
TYPES
The most common type of acne is
sometimes
known as acne vulgaris,
which almost always develops during
puberty. Chemical acne is caused by
exposure of the skin to certain chemi-
cals
and
oils.
This
results
in
the
development of acne in areas where
the chemical has come into contact
with the skin, such as on the thighs.
Certain prescribed drugs, such as
corti-
costeroid drugs,
can also cause acne.
Acne
The spots on this boy’s face are typical of acne;
the darker marks are healed spots, which fade
gradually. Severe acne may leave pits in the skin.
CAUSE
Acne spots are caused by the obstruc-
tion of hair follicles by excess sebum
(the oily substance secreted by the seba-
ceous glands). Bacteria multiply in the
follicle,
causing
inflammation.
Hor-
monal changes at puberty, including
increased levels of
androgen hormones
(male sex hormones) in both males and
females, stimulate the production of
sebum. There may also be a genetic pre-
disposition to acne.
SYMPTOMS
Acne develops in areas in which there
is a high concentration of sebaceous
glands, mainly the face, centre of the
chest,
upper
back,
shoulders,
and
around the neck. Milia (whiteheads),
comedones (blackheads), nodules (firm
swellings under the skin), and cysts
(larger, fluid-filled swellings) are the
most common types of spot. Some, par-
ticularly cystic spots, leave scars.
TREATMENT AND OUTLOOK
There
is no instant
cure for acne,
although washing the affected areas at
least twice a day with a mild soap may
The part of the
vestibulocochlear nerve
(the eighth cranial nerve) concerned
with hearing. The acoustic nerve is also
called the auditory or cochlear nerve.
A rare, noncancerous tumour arising
from supporting cells that surround the
vestibulocochlear nerve,
usually within
the internal auditory meatus (the canal
in the skull through which the nerve
passes from the inner ear to the brain).
CAUSE AND INCIDENCE
Acoustic
neuromas
most
commonly
occur in people between the ages of 40
and 60 and are slightly more common in
women than in men.
Usually, the cause of an acoustic neu-
roma is unknown. However, tumours
that affect the nerves on both sides of
the head simultaneously may be part of
a widespread
neurofibromatosis
(a dis-
ease characterized by changes in the
nervous system, skin, and bones).
SYMPTOMS
An acoustic neuroma can cause
deafness
,
tinnitus
(noises in the ear), loss of bal-
ance, and pain in the face and the
affected ear. As the tumour enlarges, it
may lead to additional complications,
such as
ataxia
(loss of coordination) due
to the compression of the brainstem
and cerebellum.
DIAGNOSIS AND TREATMENT
Diagnosis is made by
hearing tests
fol-
lowed by
X-rays
or by
CTscanning
or
MRI
(techniques that produce cross-section-
al or three-dimensional images of body
structures).
Surgery may be necessary to remove
an acoustic neuroma, but treatment
with
radiotherapy
to
shrink
it
may
also be effective.
acoustic neuroma
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