Bma Illustrated Medical Dictionary

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.

healthAt 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 centreA building owned by a

local authority and leased to general

practitioners and other healthcare pro-

fessionals as premises for their work.

health foodA term applied to any

food products thought

to promote health.

health hazardsEnvir-

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-

sufficientsupply, 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).

hearingThe sense that enables sound

to be perceived. The ear transforms the

sound waves it receives into nerve

impulses that pass to thebrain.

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 thalamusto the

superior temporal gyrus, part of the

cerebral cortex involved in perceiving

sound. (See also deafness.)

hearing aidsElectronic 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 lossA deterioration in the

ability to perceive sound. (See also

deafness.)

hearing testsTests carried out to

assess hearing. Hearing tests are per-

formed as part of a routine assessment

HEALTH HEARING TESTS

H

Chart of

results

AUDIOMETRY

HEARING TESTS

Response

button

indicating

when sound

heard

Headphones Audiometer Doctor