follow-up cystoscopy is needed. Blad-
der tumours that have spread through
the bladder wall may be treated by
radiotherapyor by surgical removal of
part or all of the bladder.
blastocystA cell cluster that develops
from a fertilized ovumand grows into
an embryo(see fertilization).
blastomycosisA type of fungal infec-
tionthat can affect the lungs and other
internal organs.
bleaching, dentalA cosmetic proce-
dure for lightening certain 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.
bleedingLoss of blood from the circu-
latory systemcaused 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 blood
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, blood collects
around the damaged blood vessels
close under the skin to form a bruise.
Any lost blood that mixes with other
body fluids such as sputum (phlegm) or
urine will be noticed quite readily; bleed-
ing in the digestive tract may make
vomit or faeces appear darker than
usual. Internal bleeding may not be dis-
covered until severe anaemiadevelops.
bleeding disordersA group of condi-
tions characterized by bleeding in the
absence of injury or by abnormally pro-
longed and excessive bleeding after
injury. The disorders result from defects
in mechanisms by which bleeding is
normally stopped: blood coagulation,
plugging of damaged blood vessels by
platelets, and constriction of blood ves-
sels (see blood clotting).
Coagulation disorders are usually due
a deficiency of or abnormality in the
enzymes(coagulation factors) involved
in blood clotting. Defects may be con-
genitalor acquired later in life. Themain congenital coagulation defects are
von Willebrand’s disease,haemophilia,
and Christmas disease.
Acquired defects of coagulation factors
may develop at any age due to severe
liver disease, digestive system disorders
that prevent the absorption ofvitamin K
(needed to make certain coagulation fac-
tors), or the use of anticoagulant drugs.
Disseminated intravascular coagulation
(DIC) is an acquired disorder that is
both complex and serious. It may be the
result of underlying infection or cancer.
In this condition, platelets accumulate
and clots form within small blood ves-
sels; coagulation factors are used up
faster than they can be replaced, and
severe bleeding may result.
Coagulation disorders are treated by
replacement of the missing factor, fac-
tors extracted from fresh blood, or fresh
frozen plasma. Genetically engineered
factors may be used. Anticoagulants are
sometimes used to suppress excess
clotting activity in DIC.
Thrombocytopenia, which results from
insufficient platelets in the blood, pro-
duces surface bleeding into the skin
and gums and multiple small bruises.
Platelet defects may be inherited, asso-
ciated with the use of certain drugs
(including aspirin), or a complication of
certain bone marrow disorders such as
myeloid leukaemia. Treatment consists
of platelet transfusions. Rarely, abnor-
mal bleeding is caused by a blood-
vessel defect orscurvy. Elderly people
and patients on long-term courses of
corticosteroid drugs may suffer mild
abnormal bruising due to loss of skin
support to the smallest blood vessels.
Treatment is rarely required.
bleeding gumsSee gingivitis.
blepharitisInflammation of the eyelids,
with redness, irritation, and scaly skin at
the lid margins. Blepharitis may cause
burning and discomfort in the eyes and
flakes or crusts on the lashes. The con-
dition is common, tends to recur, and is
sometimes associated with dandruff of
the scalp or eczema. Severe blepharitis
may lead to corneal ulcers. In many
cases, treatment of associated dandruff
with an antifungal shampoo will result
in improvement of the blepharitis.BLASTOCYST BLEPHARITISB