Webster's New World Medical Dictionary

reaction kinetics
The rate of change in a bio-
chemical (or other) reaction.
reactive airway disease
A term used to refer to
several lung conditions that are characterized by
transient narrowing (spasm) of the airways in the
lungs, for example, asthma. The narrowing limits
the ability of air to be expelled from the lungs
through the airways and leads to wheezing. See also
asthma.
reactive arthritis
A chronic form of inflamma-
tory arthritis that features arthritis, inflammation of
the eyes (conjunctivitis), and inflammation of the
genital, urinary, or gastrointestinal systems. Reactive
arthritis is the preferred name for what was formerly
called Reiter syndrome. Reactive arthritis seems to
involve an immune system that is “reacting” to the
presence of a bacterial infection in the genital, uri-
nary, or gastrointestinal system. Accordingly, certain
people’s immune systems are genetically primed to
react aberrantly when these areas are exposed to
particular bacteria. The aberrant reaction of the
random sample
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immune system leads to inflammation in the joints,
eyes, and genital, urinary or gastrointestinal system.
See also 
arthritis; arthritis, Reiter syndrome; ker-
atodermia blennorrhagicum.
reading frame
One of the three possible ways to
read a nucleotide sequence in DNA, depending on
whether reading starts with the first, second, or
third base in a triplet.
reading frame, open
See 
open reading frame.
reading retardation
Impaired ability to read.
Reading retardation may reflect mental disability,
cultural deprivation, or learning disability. See also
dyslexia.
reagent
A substance that is used to produce a
chemical reaction that allows researchers to detect,
measure, produce, or change other substances.