and plays an important role in breathing.
There are openings in the diaphragm for
the oesophagus and major nerves and
blood vessels. To inhale, the diaphragm’s
muscle fibres contract, pulling the whole
diaphragm downwards and drawing air
into the lungs. (See also breathing.)
diaphysisThe shaft, or central portion,
of a long bone, such as the femur. The
epiphysis(end of the long bone) devel-
ops independently from the diaphysis,
as they are initially separated by a mass
of cartilage known as the epiphyseal
plate. The diaphysis and epiphysis even-
tually fuse to form a complete bone.diarrhoeaIncreased fluidity, frequency,
or volume of bowel movements. It may
be acute or chronic. Diarrhoea can be
very serious in infants and elderly peo-
ple because of the risk of severe,
potentially fatal, dehydration.
Acute diarrhoea is usually a result of
consuming food or water contaminated
with certain bacteria or viruses (see food
poisoning). Infective gastroenteritisalso
causes diarrhoea and may be acquired
as a result of droplet infection. Other
causes of acute diarrhoea include anxi-
ety and, less commonly, amoebiasis,
shigellosis, typhoid feverand paratyphoid
fever, drug toxicity, food allergy, and
food intolerance.
Chronic diarrhoea is generally repeat-
ed attacks of acute diarrhoea. It may be
the result of an intestinal disorder such
as Crohn’s disease, ulcerative colitis, can-
cer of the colon (see colon, cancer of), or
irritable bowel syndrome. Diarrhoea that
recurs, persists for more than a week, or
is accompanied by blood requires med-
ical investigation.
The water and electrolytes (salts) lost
during a severe attack of diarrhoea need
to be replaced to prevent dehydration.
Ready-prepared powders of electrolytemixtures can be bought (see rehyd-
ration therapy). Antidiarrhoeal drugs,
such as diphenoxylateand loperamide,
should not be taken to treat attacks of
diarrhoea due to infection; they may pro-
long it. Drugs may help if the diarrhoea
is disabling or if there is abdominal pain.
Viral gastroenteritis in a child can
damage the lining of the intestine,
which may lead to lactose intolerance
and further diarrhoea. Seek medical
attention if diarrhoea in an infant per-
sists for more than 48 hours. Call a
doctor urgently if the infant is dehydrat-
ed. (See also rehydration therapy.)
diastole The period in the heartbeat cycle
when the heart muscle is at rest; it alter-
nates with systole, the period of muscular
contraction. (See also cardiac cycle).
diastolic pressureThe lowest level of
blood pressuremeasured in the main
arteries. Diastolic pressure is the pressure
between heartbeats when the ventricles
are relaxed and filling with blood. Sys-
tolic pressure, the highest level of blood
pressure in the arteries, occurs when
the ventricles contract. The normal range
varies with age and between individuals,
but a young adult usually has a dias-
tolic pressure of about 80 mmHg (mm
of mercury) and a systolic pressure of
around 120 mmHg. A persistently high
diastolic pressure occurs in most cases
of hypertension.
diathermyThe production of heat in a
part of the body using high-frequency
electric currents or microwaves. It can
be used to increase blood flow and to
reduce deep-seated pain. Diathermy
can also be used to destroy tumours
and diseased parts without causing
bleeding. A diathermy knife is used by
surgeons to coagulate bleeding vessels
or to separate tissues without causing
them to bleed (see electrocoagulation).
diathesisA predisposition towards cer-
tain disorders. For example, a bleeding
diathesis is present when a bleeding
disordermakes a person susceptible to
prolonged bleeding after an injury.
diazepamOne of the benzodiazepine
drugs, used mainly for the short-term
treatment of anxietyand insomnia. It is
also prescribed as a muscle-relaxant
drug, as an anticonvulsant drugin theDIAPHYSIS DIAZEPAMD
Epiphysis EpiphysisDIAPHYSISDiaphysis