Webster's New World Medical Dictionary

atrium
An entry chamber. On both sides of the
heart, the atrium is the chamber that leads to the
ventricle.
atrophic vaginitis
Thinning of the lining
(endothelium) of the vagina due to decreased pro-
duction of estrogen. Atrophic vaginitis may occur
with menopause.
atrophy
A wasting away or diminution. Muscle
atrophy is a decrease in muscle mass, often due to
extended immobility.
atropine
A drug, made from the belladonna
plant, that is administered via injection, eye drops,
or in oral form to relax muscles by inhibiting nerve
responses.
atropine psychosis
A syndrome characterized
by dry mouth, blurred vision, forgetfulness, and dif-
ficulty with urination that can be caused by the anti-
cholinergic effects of some drugs, particularly
antipsychotic medications. Treatment requires
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atropine psychosis
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reducing or stopping the medication. See also 
anticholinergic.
attack, vasovagal
See 
vasovagal reaction.
attention
The act of attending to discrete stimuli
in the environment. Learning is most efficient when
a person is paying attention. Poor attention can be a
key sign of behavior disorders in children, stress, or
depression. See also attention deficit hyperactivity
disorder.
attention deficit disorder
See 
attention
deficit hyperactivity disorder.
attention deficit hyperactivity disorder
A dis-
order in which a person is unable to control behav-
ior due to difficulty in processing neural stimuli,
accompanied by an extremely high level of motor
activity. Abbreviated ADHD. ADHD can affect chil-
dren and adults, but it is easiest to perceive during
schooling. A child with ADHD may be extremely dis-
tractible, unable to remain still, and very talkative.
ADHD is diagnosed by using a combination of par-
ent and/or patient interview, observation of the
patient, and sometimes use of standardized screen-
ing instruments. Treatments include making adjust-
ments to the environment to accommodate the
disorder, behavior modification, and the use of
medications. Stimulants are the most common
drugs used, although certain other medications can
be effective.