handednessPreference for using the
right or left hand. Some 90 per cent of
adults use the right hand for writing;
two thirds prefer the right hand for
most activities requiring coordination
and skill. The others are either left-
handed or ambidextrous (able to use
both hands equally well).
Handedness is related to the division
of the brain into 2 hemispheres, each of
which controls movement and sensa-
tion on the opposite side of the body. In
most right-handed people the speech
centre is in the left brain hemisphere.
Inheritanceis probably the most impor-
tant factor in determining handedness.
hand-foot-and-mouth diseaseAn in-
fectious disease, mainly affecting young
children, that is caused by the coxsackie-
virus. Hand-foot-and-mouth disease may
occur in small epidemics, usually in the
summer. The illness is usually mild and
lasts for only a few days. Symptoms
include blistering of the palms, soles of
the feet, and inside of the mouth, and a
slight fever. There is no treatment other
than mild analgesic drugs. The illness is
not related to foot-and-mouth disease,
which occurs in cattle.
handicapThe extent to which a physi-
cal or mental disabilityinterferes with
normal functioning and causes the per-
son to be disadvantaged.
hangnailA strip of skin torn away from
the side or base of a fingernail, expos-
ing a raw, painful area.
hangoverThe unpleasant effects that can
be experienced after over-indulgence in
alcohol, characterized by headache, nau-
sea, vertigo, and depression. Alcohol
increases production of urine, and some
of the symptoms of a hangover are due
to mild dehydration. (See also alcohol
intoxication.)
Hansen’s diseaseA chronic bacterial
infection, also called leprosy, that dam-
ages nerves, mainly in the limbs and
facial area, and may cause skin damage.
The disease is caused by a bacterium,
MYCOBACTERIUM LEPRAE, which is spread
in droplets of nasal mucus. Hansen’s
disease is not highly contagious, and a
person is infectious only in the early
stages. Prolonged close contact puts peo-
ple at risk. The disease is most prevalentin Asia, Central America, South Ameri-
ca, and Africa.
Hansen’s disease has a long incuba-
tion period – about 3–5 years. There are
2 main types: the lepromatous type, in
which damage is widespread, progres-
sive, and severe; and the tuberculoid
type, which is milder. In both types,
damage is initially confined to peri-
pheral nerves supplying the skin and
muscles. Skin areas supplied by affected
nerves become lighter or darker and
sensation and sweating are reduced. As
the disease progresses, the peripheral
nerves swell and become tender. Hands,
feet, and facial skin eventually become
numb and muscles become paralysed,
leading to deformity. Other possible
features include blindness, destruction
of bone, and sterility.
The presence of the causative bacteria
is confirmed by a skin biopsy.Drug
treatment may be with a combination
of dapsone, rifampicin, and clofazimine,
which kills most of the bacteria in a few
days. Any damage that has occurred
before treatment, however, is irrevers-
ible. Plastic surgerymay be necessary
to correct deformities; and nerve and
tendon transplants may improve the
function of damaged limbs.
hantavirusA viral infection that is trans-
mitted to humans through the urine or
faeces of infected rodents, such as rats.
Symptoms range from a minor flu-like
illness with headache and a sore throat
to high fever, nausea and vomiting, and
abnormal bleeding. Some strains of
hantavirus can cause severe infections
which may lead to kidney failure, seri-
ous lung damage, and death.
hardening of the arteriesThe popu-
lar term for atherosclerosis.
hare lipA common term for the birth
defectin which there is a split in the
upper lip due to failure of the 2 sides to
fuse during fetal development. A hare
lip is often associated with a similar
failure of the 2 halves of the palate to
join. (See also cleft lip and palate.)
Hashimoto’s thyroiditisAn autoim-
mune disorder in which the body’s
immune system develops antibodies
against its own thyroid gland cells. As
a result, the thyroid gland cannotHANDEDNESS HASHIMOTO’S THYROIDITISH