The Cardiovascular
System:
Blood
B
loodhasbeensort of a mystery for much of hu-
man history. Because our ancestors observed that
people could die from the loss of too much blood, it
was considered a “life force.” Despite this observation,
physicians from ancient times through the 18th cen-
tury practiced the technique of bloodletting, either by
directly cutting into a vein or by using leeches. The idea
was to balance the “humors,” or vital fluids, that trav-
eled in the blood. As the science of medicine advanced,
physicians realized that blood played an essential role
in carrying oxygen to body tissues. Giving blood to
trauma or surgical patients via transfusion replaced
bloodletting. With further medical advances, scientists
discovered that individuals had different blood types and
that donor blood had to match the recipient's type for the
transfusion to be successful; transfusions became safer
and saved countless lives. Today, millions of individuals
safely donate blood to others.
Despite the safety of transfusions, many places
experience shortages of available blood for health care.
Many people who would qualify do not participate in
blood donation. A single blood donation can benefit up
to four recipients, since the blood can be separated to
provide the recipients with only the blood components
they need most. Because of blood shortages, along
with the limited time that blood can be stored, scientists
have been working to create artificial blood.
Let's take a closer look at this vital substance.
NATIONAL
GEOGRAPHIC
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