LEAD POISONING
LEISHMANIASIS
lead poisoning
Damage to the
brain,
nerves,
red
blood cells,
and digestive
system, caused by inhaling lead fumes or
swallowing lead salts. Acute poisoning,
which occurs when a large amount of
lead is taken into the body over a short
period of time, is sometimes fatal.
Symptoms include severe, colicky ab-
dominal pain, diarrhoea, and vomiting.
There may also be
anaemia,
loss of
appetite, and a blue, black, or grey line
along the gum margins. Lead poisoning
may be confirmed by blood and urine
tests.
Chelating agents,
such as
penicil-
lamine
, may be prescribed.
learning
The process by which knowledge
or abilities are acquired, or behaviour is
modified. Various theories about learn-
ing have been proposed. Behavioural
theories emphasize the role of
condi-
tioning
, and cognitive theories are based
on the concept that learning occurs
through the building of abstract “cogni-
tive” models, using mental capacities
such as intelligence, memory, insight,
and understanding.
learning difficulties
Problems with
learn-
ing,
which result from a range of mental
and physical problems. Learning diffi-
culties may be either general or specific.
In general learning difficulties, all aspects
of mental and physical functioning may
be affected. Depending on the severity
of the problem, a child with general
learning difficulties may need to be
educated in a special school. Specific
learning difficulties include
dyslexia
,
dyscalculia (the inability to solve math-
ematical
problems),
and dysgraphia
(writing disorders). Causes of learning
difficulties include
deafness
,
speech dis-
orders
, and disorders of
vision
, as well
as genetic and chromosomal problems.
learning disability
A
learning difficulty
.
leech
A type of bloodsucking worm with
a flattened body and a sucker at each
end. Leeches of various types inhabit
tropical forests and waters. They bite
painlessly, introducing their saliva into
the wound before sucking blood. Leech
saliva contains an anticlotting sub-
stance called hirudin, which may cause
the wound to bleed for hours. Leeches
are sometimes used in medicine to drain
a
haematoma
from a wound.
leg, broken
See
femur, fracture of; fibula;
tibia.
legionnaires' disease
A form of
pneu-
monia
that is caused by
LEGIONELLA
pneumophila,
a bacterium that breeds
in warm, moist conditions. The source
of infection is often an air-conditioning
system in a large, public building.
The first symptoms include headache,
muscular and abdominal pain, diarrhoea,
and a dry cough. Over the next few days,
pneumonia develops, resulting in a high
fever, shaking chills, coughing up of
thick
sputum
(phlegm), drowsiness, and
sometimes
delirium
. Treatment is with
the antibiotic drug
erythromycin.
leg, shortening of
Shortening of the leg
is usually caused by faulty healing of
a fractured
femur
(thigh-bone) or
tibia
(shin). Other causes are an abnormality
present from birth, surgery on the leg, or
muscle weakness associated with
polio-
myelitis
or another neurological disorder.
leg ulcer
An open sore on the leg that
fails to heal, usually resulting from poor
blood circulation to or from the area.
There are various types of ulcer. Venous
ulcers (also referred to as varicose or
stasis ulcers) occur mainly on the ankles
and lower legs and are caused by valve
failure in veins; they usually appear in
conjunction with
varicose veins. Bedsores
(decubitus ulcers) develop on pressure
spots on the legs due to a combination
of poor circulation, pressure, and immo-
bility over a long period. Leg ulcers can
also be due to
peripheral vascular dis-
ease
and
diabetes mellitus.
In the tropics,
some infections can cause
tropical ulcers
.
leiomyoma
A noncancerous tumour of
smooth
muscle
. Leiomyomas, also called
fibroids,
usually occur in the
uterus.
More
rarely, they develop in the walls of blood
vessels in the skin, forming tender lumps.
Leiomyomas may require surgical re-
moval if they cause symptoms.
leishmaniasis
Any of a variety of dis-
eases caused by single-celled
parasites
called leishmania. These parasites are
harboured by dogs and rodents and are
transmitted by the bites of sandflies.
The most serious form of leishmaniasis
is called kala-azar or
visceral
leishmani-
asis. This disease is prevalent in some
parts of Asia, Africa, and South America,
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