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Oxygen-carrying red
blood cells make up
99 per cent of all
blood cells.Every second, two
million new red blood
cells are made by
jelly-like red marrow
inside bones.During a lifespan of
120 days, a red blood
cell travels around the
body 170,000 times –
once each minute. It is
then dismantled and
recycled by the spleen
and liver.Packed into every
red blood cell are
250 million red-
coloured haemoglobin
molecules. Each one
carries four oxygen
molecules, so a single
red blood cell can
transport one billion
oxygen molecules.The heart is made
largely of cardiac
muscle, which
does not tire.Over a lifetime of 70
years, the heart beats
2.5 billion times
without taking a rest.The heart beats, on
average, 70 times a
minute. Heart rate
can double or triple
during exercise to
get extra oxygen
to your muscles.Each person belongs
to one of four blood
groups – A, B, AB, or
O. Blood groups are
determined by tiny
“markers” carried
by red blood cells.More than 112.5 million units of blood are donated around
the world every year. Blood transfusions replace blood lost
during surgery and are used to treat some medical conditions.072_073_Blood.indd 73 03/01/19 12:09 PM