also called plasma exchange. Blood is
withdrawn from the body and the plas-
ma portion is removed by machines
called cell separators. The blood cells
are then mixed with a plasma substitute
and returned to the circulation. Plasma-
pheresis is used to remove damaging
antibodiesor antibody-antigen particles
from the circulation in autoimmune dis-
orderssuch as myasthenia gravisand
Goodpasture’s syndrome.
plasma proteinsProteins present in
blood plasma, including albumin,blood
clottingproteins, and immunoglobulins.
plasminogen activatorSee tissue plas-
minogenactivator.
plaster castSee cast.
plaster of ParisA white powder made
of a calcium compound that, when mixed
with water, produces a paste that can be
shaped before it sets. Plaster of Paris is
used for constructing castsand making
dental models (see impression, dental).
plastic surgeryAny operation carried
out to repair or reconstruct skin and tis-
sue that has been damaged or lost, is
malformed, or has changed with aging.
Plastic surgery is often performed after
severe burns or injuries, cancer, or some
operations, such as mastectomy. Congen-
ital conditions that may require plastic
surgery include cleft lip and palate, hypo-
spadias, and imperforate anus (see anus,
imperforate). Techniques include skin
grafts, skin flaps, and Z-plasty; these may
be combined with implantsor a bone
graft. Microsurgeryallows transfer of
tissue to other parts of the body. (See
also cosmetic surgery.)
-plastyA suffix meaning shaping by
surgery; performing plastic surgeryon.
plateletThe smallest type of blood cell,
also called a thrombocyte. Platelets play
a major role in blood clotting.
platyhelminthA flat or ribbon-shaped
parasitic worm. (Seeliver fluke, schisto-
somiasis, tapeworm)
play therapyA method used in the
psychoanalysisof young children, based
on the principle that all play has some
symbolic significance. Watching a child
at play helps a therapist diagnose the
source of the child’s problems; the child
can then be helped to “act out” thoughts
and feelings that are causing anxiety.
plethoraA florid, bright-red, flushed
complexion. It may be caused by dila-
tion of blood vessels, or, less commonly,
by polycythaemia.
plethysmographyA way of estimating
the blood flow in vessels by measuring
changes in the size of a body part.
pleuraA thin, 2-layered membrane, 1
layer covering the outside of the lungs
and the other lining the inside of the
chest cavity. Fluid between the layers
provides lubrication, allowing smooth
movement of the lungs during breathing.pleural effusionAn accumulation of
fluid between the layers of the pleura,
making breathing difficult. Pleural effu-
sion may be caused by pneumonia,
tuberculosis, heart failure, cancer, pul-
monary embolism, or mesothelioma.
Diagnosis is confirmed by chest X-ray.
Some fluid may be removed with a nee-
dle and syringe and examined to find
the cause. A biopsyof the pleura may
also be needed.The underlying cause is
treated and fluid may be drained off to
relieve breathing problems.
pleurisyInflammation of the pleura.
Causes include lung infections, such as
pneumonia, or, more rarely, pulmonary
embolism,lung cancer, and rheumatoid
arthritis. Pleurisy causes a sharp chest
pain, which is worse when breathing in.
Treatment is of the underlying cause,
along with analgesic drugs.
pleurodyniaPain in the chest caused
by coxsackievirus B infection. SometimesPLASMA PROTEINS PLEURODYNIA
P
PLEURALungPleuraBronchusTrachea