ALIENATION
ALLERGY
the reading ability of a person who was
previously literate. (See also
dyslexia.)
alienation
Feeling like a stranger, even
when among familiar people or places,
and being unable to identify with a cul-
ture, family, or peer group. Alienation is
common in adolescents and also occurs
in people who are isolated by cultural
or language differences. In some people,
it may be an early symptom of
schizo-
phrenia
or a
personality disorder.
alignment, dental
The movement of
teeth by using either fixed or removable
orthodontic appliances
(braces) to cor-
rect
malocclusion
(incorrect bite).
alimemazine
An
antihistamine drug,
also
known as trimeprazine, that is used
mainly to relieve itching in allergic con-
ditions such as
urticaria
and atopic
eczema.
Alimemazine
often
causes
drowsiness.
alimentary tract
The tube-like struc-
ture that extends from the mouth to the
anus (see
digestive system).
alkali
Also known as a base, an alkali is
chemically defined as a donor of hydroxyl
ions (each of which comprises an atom
of hydrogen linked to an atom of oxygen
and has an overall negative electrical
charge).
Antacid drugs,
such as sodium
bicarbonate, are alkalis. Some alkalis,
such as sodium hydroxide, are corro-
sive. (See also
acid; acid-base balance.)
alkaloids
A group of nitrogen-containing
substances obtained from plants.
Mor-
phine, codeine, nicotine,
and strychnine
(see
strychnine poisoning
) are examples.
alkalosis
A disturbance of the body's
acid-base balance
in which there is an
accumulation of alkali or a loss of acid.
There are 2 types: metabolic and res-
piratory. In metabolic alkalosis, the
increase in alkalinity may be caused by
taking too much of an
antacid drug
or
by losing a large amount of stomach
acid as a result of severe vomiting. In
respiratory alkalosis, there is a reduc-
tion in the blood level of carbonic acid
(derived from carbon dioxide). This
reduction is a consequence of
hyper-
ventilation
, which may occur during a
panic attack or at high altitudes due to
lack of oxygen. (See also
acidosis.)
alkylating agents
A class of
anticancer
drugs
.
allele
One of 2 or more different forms of
a gene that occupies a specific position
on a
chromosome
(see gene;
inheritance).
allergen
A normally harmless substance
that causes an allergic reaction (see
allergy)
in people who have become
sensitized to it. Allergens can include
foods (for example, nuts, eggs, and shell-
fish); inhaled substances such as pollen,
house dust, and fur; and some drugs.
allergy
Various conditions caused by
inappropriate or exaggerated reactions
of the
immune system
(known as hyper-
sensitivity reactions) to a variety of
substances. Many common illnesses,
such as
asthma
and allergic
rhinitis
(hay
fever), are caused by allergic reactions
to substances that in the majority of
people cause no symptoms.
Allergic reactions occur only on 2nd or
subsequent exposure to the
allergen
,
once 1st contact has sensitized the body.
The function of the immune system is
to recognize
antigens
(foreign proteins)
on the surfaces of microorganisms and
to form
antibodies
(also called immuno-
globulins) and sensitized
lymphocytes
(white blood cells). When the immune
system next encounters the same anti-
gens, the antibodies and sensitized
lymphocytes interact with them, leading
to destruction of the microorganisms.
A similar immune response occurs in
allergies, except that the immune system
forms antibodies or sensitized lymph-
ocytes
against
harmless
substances
because these
allergens
are misidenti-
fied as potentially harmful antigens.
The inappropriate or exaggerated re-
actions seen in allergies are termed
A
TYPE I HYPERSENSITIVITY
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