Webster's New World Medical Dictionary

phenylketonuria
See 
PKU.
phenylketonuria, maternal
See 
PKU, maternal.
pheresis
A procedure in which the blood is fil-
tered and separated, and a portion is retained, with
the remainder being returned to the individual.
There are various types of pheresis. For example, in
leukapheresis, the leukocytes (white blood cells)
are removed; in plateletpheresis, the thrombocytes
(blood platelets) are removed; and in plasma-
pheresis, the liquid part of the blood (the plasma)
is removed. See also 
plasmapheresis.
pheromone
An agent secreted by an individual
that produces a change in the sexual or social
behavior of another individual of the same species;
a volatile hormone that acts as a behavior-altering
agent.
Philadelphia chromosome
Abbreviated Ph, the
hallmark of chronic myeloid leukemia (CML), a
small chromosome 22 that was shortened in a
reciprocal exchange of material with chromosome
9. This translocation occurs in a cell in the bone
marrow and causes CML. It is also found in a form
of acute lymphoblastic leukemia (ALL). On a molec-
ular level the Philadelphia chromosome transloca-
tion results in the production of a fusion protein. A
large portion of a proto-oncogene, called ABL, on
chromosome 9 is translocated to the BCR gene on
chromosome 22. The two gene segments are fused
and ultimately produce a chimeric protein that is
larger than the normal ABL protein. Understanding
this process led to the development of the drug ima-
tinib mesylate (brand name: Gleevec), the first in a
new class of genetically targeted agents against
leukemia.
philtrum
The area from below the nose to the
upper lip. Normally the philtrum is grooved. In fetal
alcohol syndrome, the philtrum is flat.
phimosis
A condition in which the foreskin of
the penis is too tight to be pulled back to reveal the
glans. This usually causes no problems and nothing
needs be done. If phimosis causes obstruction of
the urinary stream, meaturia (blood in the urine),
or pain, this can require surgery to relieve the phi-
mosis. Circumcision prevents phimosis.
phlebitis
Inflammation of a vein. With phlebitis,
there is infiltration of the walls of the vein and, usu-
ally, the formation of a clot (thrombus) in the vein
(thrombophlebitis). Phlebitis in a leg, for example,
causes the leg to swell with fluid (edema). Phlebitis
can be superficial and not very serious, or it can be
deep and carry the potential for dislodging blood
clots to the lungs.