Webster's New World Medical Dictionary

355
pupil
17_189283 ch16.qxp 4/18/08 10:17 PM Page 355
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purified protein derivative (PPD)
The mate-
rial used in the skin test for exposure to tuberculo-
sis infection.
purine
One of the two classes of bases in DNA
and RNA. The purine bases are guanine (G) and
adenine (A). Uric acid, the offending substance in
gout, is a purine end product. See also 
pyrimidine.
purpura
Hemorrhage (bleeding) into the sur-
face of the skin. The area of skin with purpura is
greater than 3 millimeters in diameter. The appear-
ance of an individual area of purpura varies with the
duration of the lesions. Early purpura is red and
becomes darker, then purple, and brown-yellow as
it fades.
purpura, acute thrombocytopenic
See 
acute
thrombocytopenic purpura.
purpura, anaphylactoid
See 
anaphylactoid
purpura.
purpura, Henoch
-
Schonlein
See 
anaphylac-
toid purpura.
purpura, thrombotic thrombocytopenic
See
thrombotic thrombocytopenic purpura.
purulent
Pertaining to pus. Containing or com-
posed of pus. See also 
pus.
pus
A thick, whitish-yellow fluid that results from
the accumulation of white blood cells, liquefied tis-
sue, and cellular debris. Pus is commonly a sign of
infection or foreign material in the body.
pustulosis
A highly inflammatory skin condition
that results in large, fluid-filled, blister-like areas
(pustules). Pustulosis typically occurs on the palms
of the hands and/or the soles of the feet. The skin of
these areas peels and flakes (exfoliates).