I
AGE
aerobics
Exercises, such as swimming, jogging,
and cycling, that allow muscles to work
at a steady rate with a constant, ade-
quate supply of oxygen-carrying blood
that allows them to be sustained for
long periods.
Oxygen is needed to
release energy from the body’s stores. To
fuel aerobic exercise, the muscles use
fatty acid, burning it completely to pro-
duce energy, carbon dioxide, and water.
Anaerobic
exercise relies on a different
series
of
biochemical
reactions
to
obtain energy from the muscles’ stores
of fat and sugar. The waste products of
anaerobic exercise are acidic and, as
they accumulate in muscles, cause mus-
cle
fatigue;
high-intensity
exercises,
which are anaerobic, can be performed
only for relatively short periods.
BENEFITS OF AEROBIC EXERCISE
When performed regularly, aerobic exer-
cise improves stamina and endurance. It
encourages the growth of capillaries
(small blood vessels), thereby improving
blood supply to the cells. It improves the
body cells’ capacity to use oxygen and
increases the amount of oxygen that the
body can use in a given time.
As the body becomes fitter, the con-
dition of the heart also improves: the
heart rate becomes slower, both at rest
and during exercise; the heart muscle
becomes thicker and stronger; and the
amount of blood pumped with each
beat (the stroke volume) increases. The
overall result is that the heart needs to
do less work to achieve the same level
of efficiency in pumping blood around
the body. (See also
exercise; fitness.)
aerodontalgia
Sudden pain in a tooth brought on by a
change in surrounding air pressure.
Flying at high altitudes in lowered
atmospheric pressure can cause a pocket
of air in the dental pulp to expand and
irritate the nerve in the root. Aerodon-
talgia is more likely with improperly
fitted fillings or poorly filled root canals.
aerophagy
Excessive swallowing of air, which may
occur during rapid eating or drinking
or may be caused by anxiety. After
laryn-
gectomy
(surgical
removal
of
the
larynx), voluntary aerophagy is used to
produce oesophageal speech.
aerosol
A suspension of minute liquid or solid
particles in the air, producing a fine
mist. Some drugs are prescribed in this
form for use in an
inhaler
or in a
vapor-
izer.
(See also
solvent abuse.)
aetiology
The cause of, or the study of the various
factors involved in causing, a disease.
For some cases of a particular dis-
order,
a
specific
aetiology
can
be
identified.
For
example,
laboratory
studies may show that an attack of diar-
rhoea is the result of a particular type of
virus
or bacterium.
Other
disorders
have
a
multifactorial
aetiology:
the
causative factors of degenerative arthri-
tis,
for
example,
include
genetic
susceptibility,
repeated joint injuries,
and excess weight. On the other hand,
many disorders, such as schizophrenia,
are of unknown aetiology.
afebrile
A medical term meaning without
fever.
(See also
febrile.)
affect
A term used to describe a person’s
mood. The two extremes of affect are
elation and depression. A person who
experiences extreme moods or changes
in moods may have an
affective disorder.
Shallow or reduced affect (in which
responses to events seem flat) may be a
sign of
schizophrenia
or of an organic
brain syndrome
.
affective disorders
Mental illnesses that are characterized
predominantly by marked changes in
affect
(mood). Mood may vary over a
period of time between
mania
(extreme
elation) and severe
depression.
(See also
manic-depressive illness.)
afferent
A
term
meaning
carrying
towards.
Afferent is used mainly to describe
blood vessels that supply organs, or
nerves that carry impulses from peri-
pheral sense
receptors
to the brain and
spinal cord.
affinity
A term used to describe the attraction
between chemicals that causes them
to
bind
together,
as,
for
example,
between an antigen and an antibody
(see
immune response
). In microbiology,
affinity describes the physical similarity
between organisms (viruses, for exam-
ple). In psychology, the term refers to
attraction between two people.
aflatoxin
A poisonous substance produced by
A
spergillus llavus
moulds, which con-
taminate stored foods, especially pea-
nuts, grains, and cassava. Aflatoxin is
believed to be one of the factors respon-
sible for the high incidence of
liver
cancer
in tropical Africa.
afterbirth
The common name for the tissues that
are expelled from the uterus following
the delivery of a baby (see
childbirth).
The afterbirth consists of the
placenta
and the membranes that surrounded
the fetus.
aftercare
The medical care of a patient following
treatment, particularly after
surgery
.
afterpains
Contractions of the uterus that continue
after
childbirth.
Afterpains are normal,
indicating that the uterus is shrinking as
it should, and are experienced by many
women, especially during breast-feed-
ing. Afterpains usually disappear a few
days after the birth, but
analgesic drugs
(painkillers) may be needed.
agammaglobulinaemia
A type of
immunodeficiency disorder
in
which there is an almost complete
absence of
B-lymphocytes
and
immuno-
globulins
in the blood.
agar
An extract of certain seaweeds that has
similar properties to gelatine. Agar can
be taken for constipation to soften and
give bulk to faeces, and to relieve indi-
gestion and heartburn. It is also used as
a gelling agent in media for growing
bacterial
cultures
.
age
A person’s age is usually measured
chronologically but can also be meas-
ured in terms of physical, mental, or
developmental maturity. Age may be of
medical significance in diagnosis and in
determining treatment.
PHYSICAL AGE
The age of a fetus is known as gesta-
tional age, which can be calculated
from the date of the mother’s last men-
strual period. Alternatively, it can be
assessed by
ultrasound scanning,
which
is more accurate. The estimation of ges-
tational age is important in neonatal
paediatrics for identification of babies
A
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