scrotum resembling labia. (See also
hermaphroditism, sex determination.)
pseudomonasSpecies of rod-like bac-
teriathat live in soil and decomposing
matter. PSEUDOMONA AERUGINOSAis capa-
ble of causing disease in humans and is
present in pus from wounds.
psilocybinAn alkaloidpresent in some
mushrooms. It is a hallucinogenic drug
with properties similar to those of LSD.
psittacosisA rare illness resembling
influenzathat is caused by the microor-
ganism CHLAMYDIA PSITTACI. The disease
is contracted by inhaling dust contain-
ing the droppings of infected birds, such
as pigeons or poultry. Most cases occur
among poultry farmers, pigeon owners,
and people working in pet shops. Com-
mon symptoms are severe headache,
fever, and cough, developing a week or
more after infection. Other symptoms
may include muscle pains, sore throat,
nosebleed, lethargy, depression, and, in
some cases, breathing difficulty.
A diagnosis is made by finding anti-
bodiesagainst CHLAMYDIA PSITTACIin the
blood. Treatment is with tetracycline
antibiotic drugs. With no treatment,
death may result.
psoas muscleA muscle that bends the
hip upwards towards the chest. There are
2 parts: psoas major and psoas minor.
Psoas major acts to flex the hip and
rotate the thigh inwards. Psoas minor
bends the spine down to the pelvis.
psoralen drugsDrugs containing chem-
icals called psoralens, which occur in
some plants and are present in some
perfumes. When absorbed into the skin,
psoralens react with ultraviolet lightto
cause skin darkening or inflammation.
Psoralen drugs may be used in conjunc-
tion with ultraviolet light (a combination
called PUVA) to treat psoriasisand viti-
ligo. Overexposure to ultraviolet light
during treatment, or to too high a dose
of a psoralen drug, may cause redness
and blistering of the skin. Psoralens in
perfumes may cause photosensitivity.
psoriasisA common skin disease char-
acterized by thickened patches of red,
inflamed skin, often covered by silvery
scales. It usually appears between ages
10 and 30, tends to run in families, and
affects men and women equally.
The exact cause of psoriasis is un-
known. New skin cells are made about
10 times faster than normal. The excess
cells accumulate, forming thickened
patches covered with dead, flaking skin.
Sometimes, there is also a painful
swelling and stiffness of the joints (see
arthritis). Psoriasis tends to recur in
attacks, which may be triggered by fac-
tors such as emotional stress, skin
damage, and physical illness.
There are different forms of the disor-
der. The most common is discoid, or
plaque, psoriasis, in which patches
appear on the trunk, limbs, and scalp.
Guttate psoriasis occurs most often in
children, and consists of many small
patches that develop over a wide area
of skin. Pustular psoriasis is character-
ized by small pustules.
In most cases, the condition can be
improved with topical treatments, such
as those containing corticosteroid drugs
and coal tar. Other treatments include
dithranol ointment, PUVA, and drugs
such as methotrexate. Psoriasis is usu-
ally a long-term condition.
psych- A prefix meaning mental pro-
cesses or activities, as in psychology.
psycheA term meaning mind. (See also
psychoanalytic theory.)
psychiatryThe branch of medicine
concerned with the study, prevention,
and treatment of mental illness and
emotional and behavioural problems.
Psychiatrists usually conduct exami-
nations of physical and mental state,PSEUDOMONAS PSYCHIATRY
P
PSORIASISThickened,
inflamed skin
DISCOID PSORIASIS