lead poisoningDamage 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.
learningThe 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 difficultiesProblems 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 disabilityA learning difficulty.
leechA 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 haematomafrom a wound.leg, brokenSee femur, fracture of; fibula;
tibia.
legionnaires’ diseaseA 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 ofShortening 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-
myelitisor another neurological disorder.
leg ulcerAn 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-
easeand diabetes mellitus.In the tropics,
some infections can cause tropical ulcers.
leiomyomaA 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.
leishmaniasisAny of a variety of dis-
easescaused 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 visceralleishmani-
asis. This disease is prevalent in some
parts of Asia, Africa, and South America,LEAD POISONING LEISHMANIASISL