Bma Illustrated Medical Dictionary

edged, pink spots or patches appears

on the trunk and upper arms. It is not

contagious and mainly affects children

and young adults. Its cause is unknown.

The rash lasts for 4–8 weeks, may cause

itching, and usually clears up without

treatment. Calamine lotion or antihis-

tamine drugsmay relieve any itching.

pityriasis versicolorA common skin

condition in which patches of white,

brown, or salmon-coloured flaking skin

appear on the trunk and neck. Also

known as tinea versicolor, it is caused

by a fungus that exists on most people’s

skin. Treatment is with antifungal drugs.

pivampicillinSee penicillin drugs.

pivmecillinamSee penicillin drugs.

pizotifenAn antihistamine drugused to

prevent migraine in people with fre-

quent, disabling attacks. Adverse effects

can include nausea, dizziness, drowsi-

ness, dry mouth, and muscle pains.

Prolonged use may cause weight gain.

PKU testSee Guthrie test.

placeboA chemically inert substance

given instead of a drug. Benefit may be

gained from a placebo because the per-

son taking it believes it will have a

positive effect. As the effectiveness of

any drug may be partly due to this

“placebo effect”, many new drugs are

tested against a placebo preparation.

placentaThe organ that develops in the

uterus during pregnancy and thatlink

the blood supplies of mother and baby.

The placenta develops from the chorion.

It is firmly attached to the lining of the

woman’s uterus and is connected to the

baby by the umbilical cord. It is expelled

shortly after the baby is born.

The placenta transfers oxygen and

nutrients from the mother’s circulation

into the fetus’s circulation, and removes

waste products from the fetus’s blood

into the mother’s blood for excretion by

her lungs and kidneys. It also produces

hormones such as oestrogen, progester-

one, and human chorionic gonadotrophin

(HCG). High levels of HCG appear in the

woman’s urine during early pregnancy,

and detection of them in the urine forms

the basis of pregnancy tests.

placental abruptionSeparation of all

or part of the placenta from the wall of

the uterus before the baby is delivered.

The exact cause is not known, but pla-

cental abruption is more common in

women with long-termhypertensionand

in those who have had the condition in

a previous pregnancy or who have had

several pregnancies. Smoking and high

alcohol intake may also contribute to

the risk of placental abruption.

Symptoms usually occur suddenly and

depend on how much of the placenta has

separated from the wall of the uterus.

Theyinclude slight to heavy vaginal

bleeding, which can be severe haemor-

rhaging in complete separation; cramps

in the abdomen or backache; severe,

constant abdominal pain; and reduced

fetal movements. If the bleeding does

not stop, or if it

starts again, it may

be necessary to

induce labour (see

induction of labour).

A small placental

abruption is usu-

ally treated with

bed-rest in hospi-

tal. In more severe

cases of placental

abruption, an em-

ergency caesarean

sectionis often nec-

essary to save the

the life of the fetus.

A blood transfusion

is also sometimes

required.

PITYRIASIS VERSICOLOR PLACENTAL ABRUPTION

P

PLACENTA

Umbilical

artery

Umbilical vein

Flow of waste

from fetus’s

blood to

mother’s

Amniotic fluid

Placenta

LOCATION

Umbilical

cord

Fetus

Maternal artery Wall of uterus

Maternal vein

Chorionic

villus

Flow of oxygen and

nutrients from mother’s

blood to fetus’s

Umbilical cord

Lining of

uterus

(endometrium)

Mother’s blood

Uterus