ACHE
and upper abdomen. A foul taste in the
mouth and bad breath may arise due to
the regurgitation of food. The ability to
swallow gradually deteriorates until the
swallowing of liquids is also impeded.
DIAGNOSIS AND TREATMENT
A barium swallow (a type of
barium
X-ray examination)
and
gastroscopy
(in
which a narrow viewing tube is passed
down the oesophagus) may be perfor-
med in order to investigate achalasia.
Drug treatment for achalasia is rarely
successful. It is possible to widen the
oesophagus for prolonged periods by
oesophageal dilatation
(passing a cylin-
drical rod or a
balloon catheter
down the
oesophagus). Surgery to cut some of
the muscles at the stomach entrance
may be necessary to widen the passage-
way for food.
ache
A continuous, fixed, and often dull pain
that is distinct from twinges. (See also
bone pain
;
earache
;
headache
;
stomach-
ache; toothache.)
Achilles tendon
The tendon that raises the heel. The
Achilles tendon is formed from the calf
muscles (the gastrocnemius, soleus, and
plantaris muscles) and is attached to the
calcaneus
(the heel-bone). The Achilles
tendon is named after Achilles, the leg-
endary Greek hero who was vulnerable
only in his heel.
Minor injuries to the Achilles tendon
are common. They are usually provoked
by too much exercise, faulty running
technique, or the wearing of unsuitable
footwear. All of these injuries can result
in inflammation of the tendon
(tendin-
itis)
and tearing of the tendon fibres. In
most cases, these conditions clear up
with rest and physiotherapy.
Violent stretching of the Achilles ten-
don can cause it to rupture, creating a
snapping sensation in the injured area,
and pain, swelling, and impaired move-
ment of the affected part. In such cases,
surgical repair may be needed, but
immobilization of the ankle in a plaster
cast may be sufficient.
achlorhydria
Absence of stomach acid secretions.
This may be due to chronic atrophic
gastritis
or to an absence or malfunction
of acid-producing parietal cells in the
stomach lining.
Achlorhydria may not produce symp-
toms and is not in itself a cause for
concern. However, it is sometimes asso-
ciated with
stomach cancer
and is also a
feature of pernicious anaemia, a blood
disorder caused by defective absorption
of vitamin B12 from the stomach (see
anaemia, megaloblastic).
achondroplasia
A rare genetic disorder of bone growth
that leads to
short stature.
Individuals
affected with achondroplasia have short
limbs, a well-developed trunk, and a
head of normal size, except for a pro-
truding forehead.
The condition is caused by a defect of
a dominant gene (see
genetic disorders)
but often arises as a new
mutation
,
rather than being inherited from a par-
ent. The long bones of the arms and
legs are affected mainly. The cartilage
that links each bone to its epiphysis
(the growing area at its tip) is converted
to bone too early, preventing further
limb growth.
Achondroplasia is usually obvious at
birth or during the first year of life and
no treatment is available to alter the
outlook. Intelligence and sexual devel-
opment are not affected, and lifespan is
close to normal.
aciclovir
An
antiviral drug
that can be taken orally
in tablet or liquid form, applied to the
skin as a cream, taken as eye-drops, or
given intravenously for viral infections
including
herpes simplex
(cold sores),
herpes zoster
(shingles), and varicella
zoster
(chickenpox)
in adults.
Aciclovir can be used as a life-saving
treatment for
encephalitis
(inflammation
of the brain). When it is used to treat
cold sores
or recurrent genital herpes,
for which an ointment is available over
the counter, aciclovir does not provide a
cure but does, however, reduce the
severity of the attacks.
Side effects of aciclovir are uncom-
mon, but they can include nausea,
vomiting, and fatigue. Local reactions
commonly occur after topical use.
acid
A substance that is defined as a donor
of hydrogen
ions
(hydrogen
atoms
with positive electrical charges). Acid
molecules, when mixed with or dis-
solved in water, split up to release their
constituent ions; all acids release hydro-
gen as the positive ion (positive ions are
known as cations; and negative ions are
called anions).
Examples of acids within the body
include hydrochloric acid (a corrosive
mineral acid that is produced by the
stomach lining),
and many
organic
acids,
such
as lactic
acid,
carbonic
acid, ascorbic acid (vitamin C), and
pyruvic
acid.
(See
also
acid-base
balance; alkali.)
acid-base balance
A combination of mechanisms that ens-
ures that the body’s fluids are neither
too
acid
nor too alkaline
(alkalis
are also
called bases). The body functions nor-
mally only when its fluids are close to
chemical neutrality.
Metabolic processes
cause
fluctua-
tions in the acidity and alkalinity of the
blood and other body fluids. The body
has three mechanisms for maintaining
of normal acid-base balance: buffers,
breathing, and the activities of the kid-
neys. Buffers are substances in the blood
that neutralize acid or alkaline wastes.
Rapid breathing increases the rate at
which
carbon dioxide is
eliminated
from the blood, resulting in the blood
becoming less acidic; slow breathing
has the opposite effect; the kidneys help
to maintain a constant acidity level in
the blood by regulating the amounts of
acid or alkaline wastes in the urine.
Disturbances of the body’s acid-base
balance result in either
acidosis
(exces-
sive blood acidity) or
alkalosis
(excessive
blood alkalinity).
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