HEALTH
HEARING TESTS
H
new cells can be made accumulate at
the site of damage. Fibrous tissue is
laid down within the blood clot to form
a supportive structure, and any dead
cells are broken down and absorbed by
the white blood cells. Some tissues,
such as bone and skin, are then able to
regenerate by the proliferation of new
cells around the damaged area. In skin
injuries, the fibrous tissue shrinks as
new skin forms underneath. The tissue
hardens to form a scab, which falls off
when new skin growth is complete. A
scar may remain.
An inadequate blood supply or persis-
tent infection prevents regeneration, and
some tissues, such as nerve tissue, may
be unable to regenerate. In these cases,
the fibrous tissue may develop into tough
scar tissue, which keeps the tissue struc-
ture intact but may impair its function.
health
At its simplest, the absence of
physical and mental disease. A wider
concept promoted by the World Health
Organization is that all people should
have the opportunity to fulfil their
genetic potential. This includes the
ability to develop without the impedi-
ments of poor nutrition, environmental
contamination, or infectious diseases.
(See
diet and disease; health hazards.
)
health centre
A building owned by a
local authority and leased to general
practitioners and other healthcare pro-
fessionals as premises for their work.
health food
A term applied to any
food products thought
to promote health.
health hazards
Envir-
onmental
factors that
are known to cause, or
are suspected of caus-
ing, disease. The main
types of health hazard
are:
infectious disease
(see
bacteria;
fungal
infec-
tions; insects and disease;
viruses
;
zoonosis
); an in-
sufficient supply, or the
contamination, of food
and
water
(see
food
additives; food-borne in-
fection
;
food poisoning
);
work-related hazards (see
occupational disease and
injury
); hazards associated with domes-
tic and social life; tobacco-
smoking
and
alcohol
; and global environmental haz-
ards (see
pollution
;
radiation hazards
;
sunlight, adverse effects of
).
hearing
The sense that enables sound
to be perceived. The
ear
transforms the
sound waves it receives into nerve
impulses that pass to the
brain
.
Each ear has 3 distinct regions: the
outer, middle, and inner ear. Sound
waves are channelled through the ear
canal to the middle ear, from where a
complex system of membranes and tiny
bones conveys the vibrations to the
inner ear. The vibrations are converted
into nerve impulses in the
cochlea.
These impulses travel along the auditory
nerve to the medulla of the brain. From
there, they pass via the
thalamus
to the
superior temporal gyrus, part of the
cerebral cortex involved in perceiving
sound. (See also
deafness.)
hearing aids
Electronic devices that
improve hearing in people with certain
types of
deafness
. A hearing aid consists
of a tiny microphone (to pick up sounds),
an amplifier (to increase their volume),
and a speaker (to transmit sounds).
(See also
cochlear implant.)
hearing loss
A deterioration in the
ability to perceive sound. (See also
deafness.)
hearing
tests
Tests
carried
out to
assess
hearing.
Hearing tests are per-
formed as part of a routine assessment
HEARING TESTS
AUDIOMETRY
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