The majority of miscarriages occur in
the first 12 weeks of pregnancy, and may
be mistaken for a late menstrual period.
Miscarriages may occur because of
chromosomal abnormalitiesor develop-
mental defects in the fetus, or because
of severe illness, exposure to toxins, or
an autoimmune disorder in the mother.
Miscarriages later in pregnancy may be
caused by genetic disorders, cervical
incompetence, a defect in the uterus, or
large uterine fibroids.
The symptoms are heavy bleeding with
cramping. Slight blood loss with severe
pain can be a symptom of either a threat-
ened miscarriage or ectopic pregnancy.
Miscarriages are classified medically
as different types of abortion. In a
threatened abortion, the fetus remains
alive in the uterus. In an inevitable
abortion, the fetus dies and is expelled
from the uterus. In a missed abortion,
the fetus dies but remains in the uterus.
A pelvic examinationand ultrasound
scanningmay be performed to assess
the pregnancy. If all of the contents of
the uterus are expelled, no further treat-
ment may be necessary. Otherwise, a D
and Cmay be performed. Missed abor-
tion requires a D and C or induction of
labourdepending on the duration of the
pregnancy. Rh-negative women are
given anti-D (Rho) immunoglobulin to
prevent complications related to Rhesus
incompatibility in future pregnancies.
(See also abortion.)
misoprostolA synthetic prostaglandin
drugthat inhibits gastric secretion. Miso-
prostol is used to prevent and treat
peptic ulcers associated with use of
nonsteroidal anti-inflammatory drugs.
mites and diseaseMites are small ani-
mals, usually less than 1.2 mm, with 8
legs. Many species have piercing and
blood-sucking mouthparts.
Species causing disorders include the
scabiesmite, which burrows in human
skin causing intense itching; the house-
dust mite, which can cause asthma
when inhaled in dust; and chiggers
(American harvest mites), which are
found in thick grass and cause an itchy
rash when they bite. Mites in grain or
fruit may cause skin irritation, some-
times known as grocers’ or bakers’ itch.Certain mites transmit diseases, partic-
ularly scrub typhusand rickettsial pox.
mitochondriaSmall organellesthat are
found inside cells, in which cell respira-
tiontakes place. The mitochondrial wall
consists of 2 membranes, and the inner
one is highly folded to provide a surface
for the respiration reactions. Cells that
use a lot of energy, such as muscle
cells, contain many mitochondria.
mitochondrial DNAMitochondria have
their own DNA. In human mitochondria,
the DNA is a double-helical circle that
codes for 13 proteins. Mitochondria
have a distinctive genetic code, and
their genomes are not changed by
meiosis during reproduction, making
the DNA useful in genetic studies.
The significance of mitochondria hav-
ing their own DNA is that diseases can
be inherited via abnormalities of mito-
chondrial DNA, and inheritance of the
DNA is maternal, directly from the egg.
mitosisA type of cell division in which
the chromosomeswithin the nucleus of
a cell are exactly duplicated into each of
2 daughter cells.
Before cell division, the chromosomes
duplicate themselves and coil up with
the 2 copies joined together. The dou-
bled chromosomes line up in the centre
of the cell and are pulled apart to oppo-
site ends of the cell, which then divides.
Each daughter cell therefore has the
same chromosome content as the origi-
nal cell. (See also meiosis.)
mitral incompetenceFailure of the
mitral valveof the heartto close properly,
allowing blood to leak back into the left
atrium (upper chamber) when pumped
out of the left ventricle (lower cham-
ber). The disorder, which is also known
as mitral regurgitation, may occur in
conjunction with mitral stenosis.
Symptoms include increasing breath-
lessness and fatigue, sometimes with
palpitations. Later, the ankles may swell.
Diagnosis may be made by hearing a
characteristic heart murmur, and from
chest X-rays, ECG, and echocardiography.
Cardiac catheterizationmay also be per-
formed. Treatment may include diuretic
drugs,vasodilator drugs, and anticoagu-
lant drugs. If symptoms are disabling,
heart-valve surgerymay be considered.MISOPROSTOL MITRAL INCOMPETENCEM