Bma Illustrated Medical Dictionary

placenta praeviaImplantation of the

placentain the lower part of the uterus,

near or over the cervix. Placenta praevia

occurs in about 1 in 200 pregnancies. It

varies in severity from marginal placen-

ta praevia, when the placenta reaches

the edge of the cervical opening, to

complete placental praevia, when the

entire opening of the cervix is covered.

Mild placenta praevia may have no

adverse effect. More severe cases often

cause painless vaginal bleeding in late

pregnancy. If the bleeding is slight and

the pregnancy still has several weeks to

run, bed rest in hospital may be all that

is necessary. The baby will probably be

delivered by caesarean sectionat the

38th week. If the bleeding is heavy or if

the pregnancy is near term, an immedi-

ate delivery is carried out.

placenta, tumours ofSee choriocarci-

noma; hydatidiform mole.

plagueA serious infectious disease that

is caused by the bacterium YERSINIA

PESTIS. It mainly affects rodents but can

be transmitted to humans by flea bites.

There are 2 main types: bubonic and

pneumonic plague. Bubonic plague is

characterized by swollen lymph glands

(called “buboes”). Symptoms usually

start 2–5 days after infection, with fever,

shivering, and severe headache. Soon,

the smooth, red, intensely painful bu-

boes appear, usually in the groin. There

may be bleeding into the skin around

the buboes, causing dark patches.

Pneumonic plague affects the lungs and

can spread from person to person in in-

fected droplets expelled during coughing.

Symptoms are severe coughing that pro-

duces a bloody, frothy sputum and

laboured breathing. Without early treat-

ment, death is almost inevitable.

A sample of fluid from a bubo, or a

sputum sample, is taken to confirm the

diagnosis. Possible treatments include

streptomycinand tetracycline drugs.

plantar fasciitisFasciitisof the sole of

the foot.

plantar wartSee wart, plantar.

plants, poisonousSeveral species of

plant, including foxglove, holly, deadly

nightshade, and laburnum, are poison-

ous. Nettles, hogweed, poison ivy, and

primula cause skin reactions, including

rash and itching, on contact. Young chil-

dren are the most commonly affected.

Symptoms of poisoning vary according

to the plant but may include abdominal

pain, vomiting, flushing, breathing diffi-

culties, delirium, and comaand require

urgent medical advice. Skin reactions

can be treated by application of alcohol

or calamine lotion;corticosteroid drugs

may be prescribed for severe reactions.

Poisoning usually requires gastric lavage.

Fatal poisoning is rare. (See also mush-

room poisoning.)

plaqueThe term given to an area of

atherosclerosis. The plaques are symp-

tomless until they are large enough to

reduce blood flow or until the surface of

a plaque is disturbed, causing thrombo-

sis. Plaques in coronary arteries cause

coronary artery disease.

plaque, dentalA rough, sticky coating

on the teeth consisting of saliva, bacte-

ria, and food debris. It is the chief cause

of tooth decay (see caries, dental) and

gingivitis, and forms the basis of a hard

deposit (see calculus, dental). Some of

the microorganismsin plaque, particu-

larly STREPTOCOCCUS MUTANS, break down

sugar in the remains of carbohydrate

food that sticks to the mucus, creating

an acid that can erode tooth enamel.

plasmaThe fluid part of bloodthat

remains if the blood cells are removed.

plasmapheresisA procedure for the

removal or reduction in concentration

of unwanted substances in the blood;

PLACENTA PRAEVIA PLASMAPHERESIS

P

PLACENTA PRAEVIA

Placenta

MARGINAL

PLACENTA PRAEVIA

Cervix

COMPLETE

PLACENTA PRAEVIA

Uterus Amniotic fluid

Placenta Cervix