BLEEDING DISORDERS
oxygen-depleted blood to the lungs. The
improved blood oxygen levels allow the
child to survive and grow until correc-
tive surgery is possible.
bland diet
An easily digested diet that is free from
possible irritants to the digestive tract,
such as spicy foods and raw vegetable
fibre. A bland diet is often advised
following abdominal surgery
or for
people with gastrointestinal disorders.
blast cell
An immature
cell
that later develops
into a specialized cell. For example,
white blood cells
begin as blast cells in
the bone marrow and eventually form
different types of mature white blood
cells that are then released into the
bloodstream. The presence of certain
blast
cells
may
indicate
illness.
For
example, blast cells are found in the
blood in acute leukaemia (see
leukae-
mia, acute).
(See also
stem cell.)
blast injury
Tissue damage due to the effects of blast
waves generated by an explosion. The
eardrums and digestive tract are particu-
larly at risk; the air within the ear and
hollow parts of the gut transmits the
waves in all directions, often resulting
in severe damage.
blastocyst
A cell cluster that develops from a fertil-
ized
ovum
and grows into an
embryo
(see
fertilization).
blastomycosis
A type of
fungal infection
that can affect
the lungs and other internal organs.
bleaching, dental
A cosmetic procedure for lightening cer-
tain types of
discoloured teeth,
including
nonvital “dead” teeth. The surface of the
affected tooth is painted with oxidizing
agents and then exposed to ultraviolet
light. A home procedure, consisting of
trays loaded with bleaching material, is
also available but is slower.
bleb
Another term for a
blister.
bleeding
Loss of blood from the
circulatory system
,
which may be caused by damage to the
blood vessels or by a
bleeding disorder
.
Bleeding may be visible (external) or
concealed (internal). Rapid loss of more
than 10 per cent of the blood volume
can cause symptoms of
shock,
with
fainting, pallor, and sweating.
The speed with which blood flows
from a cut depends on the type of vessel
damaged: blood usually oozes from a
capillary, flows from a vein, and spurts
from an artery. If an injury does not
break open the skin, the blood collects
around the damaged blood vessels just
beneath the skin and forms a
bruise
.
Any lost blood that mixes with other
body fluids such as sputum (phlegm)
or urine will usually be noticed quite
readily; bleeding from the lining of the
digestive tract may make vomit or faeces
appear darker than usual. Internal bleed-
ing may not be discovered until severe
anaemia
develops.
bleeding disorders
A group of conditions characterized by
bleeding in the absence of injury or
by abnormally prolonged and excessive
bleeding following injury. Bleeding dis-
orders are the result of defects in the
mechanisms by which bleeding is nor-
mally stopped: the coagulation of blood,
the plugging of damaged blood vessels
by platelets (the smallest type of blood
cell), and the constriction of blood ves-
sels (see
blood clotting).
Defects in the coagulation system
tend to cause deep bleeding into the
gastrointestinal tract, muscles, and joint
cavities. Defects of the platelets or blood
vessels usually cause superficial bleed-
ing into the skin, the gums, or the lining
of the intestine or the urinary tract.
COAGULATION DEFECTS
These disorders are usually due to a
deficiency of or abnormality in the
enzymes
(coagulation factors) that are
involved in blood clotting. Clot forma-
tion is very slow and the clots are weak
and do not seal blood vessels securely.
Coagulation defects may be
congenital
(present at birth) or may be acquired
later in life.
Congenital
The main congenital coag-
ulation defects are
haemophilia
,
Christmas
disease,
and
von Willebrand’s disease.
In
all of these, one coagulation factor is
either absent from the blood or present
only in small amounts. Haemophilia
and Christmas disease are similar disor-
ders, resulting from deficiencies of two
different coagulation factors: factor VIII
and factor IX respectively. Inheritance of
these disorders is sex-linked (see
genetic
disorders
) and normally only males are
affected. Von Willebrand’s disease is an
inherited disorder in which there is a
platelet and a factor VIII defect; it affects
both sexes about equally.
Individuals with one of these dis-
orders
may
suffer
from
bruising,
internal
bleeding,
abnormally
heavy
menstrual periods, and excessive bleed-
ing from wounds. In severe cases, there
may be recurrent bleeding into joints,
such as the knee.
Acquired
Acquired
defects
of blood
coagulation factors may develop at any
age due to severe liver disease, digestive
system disorders that prevent the ab-
sorption of
vitamin K
(which is needed to
make certain coagulation factors), or
the use of
anticoagulant drugs.
Disseminated intravascular coagula-
tion (DIC) is an acquired disorder that
is complex and serious. It may be the
result of an underlying infection or of a
cancerous tumour. In this condition,
platelets accumulate and clots develop
within small blood vessels; coagulation
factors are used up faster than they are
able to be replaced, and severe bleeding
may result.
Tests and treatment
Coagulation disor-
ders are investigated by
blood-clotting
tests.
If such a disorder is severe, it is
treated by replacing the missing factor.
Factors are extracted from fresh blood
or from fresh frozen plasma, or geneti-
cally engineered factors may be used.
Paradoxically, anticoagulants are some-
times used to suppress excess clotting
activity in DIC, which results in a
reduction in bleeding.
PLATELET DEFECTS
Bleeding may occur if there are too few
platelets in the blood, a condition called
thrombocytopenia.
The main feature of
this disorder is surface bleeding into the
skin and gums, and there are multiple
small bruises.
Occasionally, the platelets are present
in normal numbers but function abnor-
mally, causing bleeding. Platelet defects
may be inherited, they may be associated
with the use of certain drugs (including
aspirin
), or arise as a complication of
certain bone marrow disorders such as
leukaemia.
Platelets can be destroyed by
autoimmune disorders
that may have been
triggered by an infection or by drug
treatment.
Platelet defects are investigated by
blood tests. Bleeding due to a lack of
platelets may be treated with intravenous
platelet transfusions. In some cases, oral
corticosteroid drugs
are prescribed.
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