severe learning difficulties. All newborn
babies are given the Guthrie testfor
phenylketonuria. Affected babies show
few signs of abnormality, but, unless
phenylalanine is avoided, they develop
neurological disturbances including epi-
lepsy. They may have blonde hair and
blue eyes, and their urine may have a
mousy odour. Many have eczema.
Phenylalanine is found in most protein-
containing foods and in artificial sweet-
eners. A specially modified diet is
generally recommended throughout life,
(and especially during pregnancy, be-
cause high phenylalanine levels in the
mother can damage the fetus).
phenytoinAn anticonvulsant drugused
to treat epilepsyand trigeminal neuralgia.
Side effects include nausea, dizziness,
tremor, and overgrown and tender gums.
pheromoneA substance with a particu-
lar odour that, when released in minute
quantities by an animal, affects the
behaviour or development of other indi-
viduals of the same species.
phimosisTightness of the foreskin, pre-
venting it from being drawn back over the
glans(head) of the penis. In uncircum-
cised babies, some degree of phimosis is
normal, but it usually improves by age 3
or 4. In some boys, the condition persists
and may cause the foreskin to balloon
out on urination. Attempts to retract a
tight foreskin may make the condition
worse. Phimosis may also develop in
adult men, causing painful erection that
may lead to paraphimosis. Proper clean-
ing of the glans may not be possible, so
balanitis may develop. Treatment in both
adults and children is by circumcision.
phlebitisInflammation of a vein. A clot
often develops, in which case the condi-
tion is termed thrombophlebitis.
phlebographyThe obtaining of X-ray
images of veins that have been injected
with a radiopaque substance. An alter-
native name is venography.
phlebotomyPuncture of a vein to remove
blood (see venepuncture; venesection.)
phlegmSee sputum.
phobiaA persistent, irrational fear of,
and desire to avoid, a particular object
or situation. Many people have minor
phobias. A phobia is considered a psy-
chiatric disorder when it interferes with
normal social functioning. Simple pho-
bias (specific phobias) are the most
common. These may involve fear of par-
ticular animals or situations, such as
enclosed spaces (claustrophobia). Animal
phobias usually start in childhood, but
others develop at any time. Treatment
depends on the severity of the condi-
tion and the wishes of the individual.
Agoraphobiais a more serious phobia,
often causing severe impairment. The
disorder usually starts in the late teens
or early 20s. Social phobia is fear of being
exposed to scrutiny, such as a fear of
eating or speaking in public. This disor-
der usually begins in late childhood or
early adolescence.
Causes of phobias are unknown. Sim-
ple phobias are thought by some to be
a form of conditioning. For example, a
person with a fear of dogs may have
been frightened by a dog in childhood.
Exposure to the feared object or situa-
tion causes intense anxietyand, in some
cases, a panic attack. Phobias may be
associated with depressionor obsessive–
compulsive behaviour. Treatment may be
with behaviour therapyand sometimes
antidepressant drugs.
phocomeliaA limb defect in which the
feet and/or the hands are joined to the
trunk by short stumps. The condition is
extremely rare, but used to occur as a
side effect of women taking the drug
thalidomidein early pregnancy.
pholcodineA cough suppressant.
phosphatesSalts that are essential in
the diet. A phosphate compound called
ATP stores energy in cells.
phosphorusAn essential mineral, pre-
sent in many foods, including cereals,
dairy products, and meat. In the body,
phosphorus is combined with calcium
to form the bones and teeth.
photocoagulationDestructive heating
of tissue by intense light focused to a
fine point, as in laser treatment.
photophobiaAn uncomfortable sensi-
tivity or intolerance to light. It occurs
with eye disorders, such as corneal abra-
sion,and is a feature of meningitis.
photorefractive keratectomy A sur-
gical treatment for astigmatism,myopia,
and hypermetropia, in which areas of
the corneaare shaved away by laser.PHENYTOIN PHOTOREFRACTIVE KERATECTOMY
P