bloodstream. The substances are taken
up in greater concentrations by tissues
that are more metabolically active. The
substances emit positrons, which release
photons that are detected by the scan-
ner. PET scans are used to detect brain
tumours, locate epileptic activity within
the brain, and examine brain function.
Peutz-Jeghers syndrome A very rare,
inherited condition in which
in the gastrointestinal tract and small,
flat, brown spots appear on the lips and
in the mouth. Occasionally the polyps
bleed, or cause abdominal pain or
polyps may be removed.
peyote A cactus plant found in northern
Mexico and the southwest of the US. Its
dried blossoms are used to prepare the
Peyronie's disease A disorder of the
in which part of the sheath of
fibrous connective tissue thickens, caus-
ing the penis to bend during erection.
This commonly makes intercourse diffi-
cult and painful. Eventually, some of the
penile erectile tissue may also thicken.
Men over 40 are most often affected.
The cause is unknown. The disease may
improve without treatment. Otherwise,
local injections of
or surgical removal of the thickened area
and replacement with normal tissue may
be carried out.
pH A measure of the acidity or alkalinity
of a solution. The pH scale ranges from
0-14, 7 being neutral; values smaller than
this are acid, values larger are alkaline.
The pH of body fluids must be close to
7.4 for metabolic reactions to proceed
phaeochromocytoma A rare tumour of
cells that secrete
The tumour causes increased produc-
tion of these hormones, leading to
. The tumours usually devel-
op in the
(core) of the
, and are most common in young
to middle-aged adults.
Hypertension is the only sign most of
the time, but pressure on the tumour,
emotional upset, change in posture, or
can cause a
surge of hormones. This surge brings on
a sudden rise in blood pressure,
, headache, nausea, vomiting, facial
flushing, sweating, and, sometimes, a
feeling of impending death.
are used to
make a diagnosis.
CT scanning, MRI,
may be used
to locate the tumours, which are then
usually removed surgically. Follow-up
medical checks are required because
the condition occasionally recurs.
phagocyte A cell in the
that can surround, engulf, and digest
, foreign particles, and
cellular debris. Phagocytes are found in
alveoli (small air sacs) within the lungs.
phalanges The small bones that make
up the fingers, thumb, and toes. The
thumb and big toe have 2 phalanges; all
the other fingers and toes have 3.
phalanx A term for any of the bones in
the fingers or the toes.
phallus Any object that may symbolize
phantom limb The
limb is still present after amputation.
pharmaceutical Any medicinal drug.
The term is also used in relation to the
manufacture and sale of drugs.
pharmacognosy The study or knowl-
edge of the pharmacologically active
ingredients of plants.
pharmacokinetics The term used to
describe how the body deals with a
pharmacology The branch of science
that is concerned with the discovery and
; their chemical
composition; their actions; their uses;
and their side effects and toxicity.
pharmacopoeia Any book that lists
and describes most medicinal drugs,
especially an official publication, such
as the British Pharmacopoeia (BP).
A pharmacopoeia describes sources,
preparations, and doses of drugs. There
may also be information on how drugs
work and on possible adverse effects.
pharmacy The practice of preparing
drugs, and making up and dispensing
prescriptions. Also, a place where these
activities are carried out.
pharyngeal diverticulum An alterna-
tive term for a