I
AMOXAPINE
scanning,
from the
amniotic sac
(the
membrane that surrounds the
fetus
in
the
uterus).
WHY IT IS DONE
The amniotic fluid contains fetal cells,
which can be subjected to
chromosome
analysis
in order to identify or exclude
chromosomal defects, such as
Down’s
syndrome,
or genetic analysis to look for
genetic disorders
such as
haemophilia,
cystic fibrosis,
and
Tay-Sachs disease.
The
amniotic fluid also contains chemicals;
and analysis of the fluid can help to
diagnose
or
exclude
developmental
abnormalities such as
spina bifida.
The
severity
of
rhesus incompatibility
and
the maturity of the fetal lungs can also
be checked by amniocentesis.
HOW IT IS DONE
Amniocentesis is usually performed in
the 14th to 18 th week of pregnancy. It
may be performed earlier, but this is
technically more difficult a this early
stage. The skin
of the abdomen is
cleaned and a needle is inserted into the
amniotic sac; (in all cases, ultrasound
scanning is used to avoid contact with
the fetus and placenta). An attached
syringe
removes some fluid for analysis.
COMPLICATIONS
Amniocentesis slightly increases the risk
of
miscarriage
or early rupture of the
membranes, and the procedure is there-
fore recommended only when the fetus
is thought to be at increased risk of an
abnormality.
(See also
antenatal care,
chorionic villus sampling.)
Procedure for amniocentesis
A needle, guided by ultrasound, is introduced
through the uterine wall into the amniotic sac;
a sample of amniotic fluid is then withdrawn.
amnion
One of the membranes that surrounds
the
fetus
in the uterus.The outside of the
amnion is covered by another mem-
brane called the
chorion.
amniotic fluid
The clear, watery fluid (popularly called
the “waters”) that surrounds the
fetus
in the
uterus
and is contained within the
amniotic sac
(a thin, membranous bag).
Amniotic
fluid
cushions
the
fetus
against
pressure
from
the
mother’s
internal organs, allowing movement.
Amniotic fluid is produced by cells
that line the amniotic sac and is con-
stantly circulated. The fetus swallows
the fluid, which is absorbed into the
fetal bloodstream and then excreted by
the kidneys as urine. The fluid is 99 per
cent water. The remainder consists of
dilute concentrations of the substances
found in
blood
plasma, along with cells
and
lipids
(fats) from the fetus.
Amniotic fluid appears during the
first week following conception, and it
gradually increases in volume until the
tenth week, when it increases very
rapidly. After approximately 35 weeks’
gestation, the volume of fluid slowly
starts to decline.
In a small number of pregnancies,
polyhydramnios
(the formation of exces-
sive amounts of amniotic fluid) occurs;
less frequently,
oligohydramnios
(the for-
mation of insufficient fluid) occurs.
amniotic sac
The membranous bag that surrounds
the
fetus
and is filled with
amniotic fluid
as pregnancy advances. The sac is made
up of two membranes, the inner
amnion
and the outer
chorion.
amniotomy
Artificial rupture of the amniotic mem-
branes. Amniotomy, which is popularly
known as “breaking of the waters”, is
performed for
induction of labour
.
amoeba
A type of protozoon (see
protozoa).
An
amoeba is a microscopic single-celled
organism with an irregular, changeable
shape. Amoebae live in moist environ-
ments such as fresh water and soil.
Some types are parasites of humans,
causing diseases such as
amoebiasis
.
amoebiasis
An infection caused by the amoeba
E
ntamoeba
histolytica
,
a tiny single-
celled parasite that lives in the human
large intestine. Amoebiasis is spread
through eating food or drinking water
contaminated by human excreta con-
taining cysts of the amoeba.
Once the cysts are swallowed, the
cyst walls break down, and the amoe-
bae hatch out to parasitize the large
intestine. In the intestine, the amoebae
multiply and develop protective cap-
sules, forming new cysts. These cysts
are passed out of the body in the faeces
and can survive for long periods before
the next person acquires them.
SYMPTOMS
Some individuals carry the E
ntamoeba
histolytica
parasite in their intestines
and excrete cysts without having symp-
toms. However, some strains of the
amoebae invade and ulcerate the intes-
tinal
wall,
causing
diarrhoea
and
abdominal pain, which may develop
into full-blown
dysentery.
The amoebae may spread through
the bloodstream to the liver or, rarely, to
the brain or lung, where they cause
abscesses.
Symptoms
of an amoebic
liver abscess include weight loss, chills,
fever, and painful liver enlargement.
Liver abscesses
may also sometimes
occur in the absence of symptoms.
PREVENTION AND TREATMENT
Travellers to countries where sanitary
standards are low can reduce their risk
of acquiring amoebiasis by drinking
only bottled or thoroughly boiled water
and by not eating uncooked vegetables
or unpeeled fruit.
Treatment of all forms of amoebiasis
is with drugs such as
metronidazole
or
diloxanide. These drugs kill the parasite
within a few weeks, leading to com-
plete recovery.
amoebic dysentery
See
amoebiasis
.
amoebicides
A group of drugs that are used to treat
amoebiasis.
Examples of amoebicides
are diloxanide and
metronidazole.
The
drugs work by killing amoebae (see
amoeba
) in the intestine and in other
body tissues.
amoxapine
A tricyclic
antidepressant drug.
Possible
adverse effects of amoxapine include a
dry mouth, blurred vision, dizziness,
drowsiness, abnormal muscular move-
ments,
menstrual
irregularities,
and
enlargement of the breasts.
A
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