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Found in humans and most animals, blood is an incredibly important bodily
fluid that transports oxygen and various nutrients to our body’s cells.
Blood makes up around 7% of the
weight of a human body and contains red blood cells, white blood cells and
platelets. These blood cells float in a yellow liquid called blood plasma.
Blood plasma is made up of 90% water and also contains various nutrients,
electrolytes, gases, proteins, glucose and hormones. Blood plasma can be
separated from the cells by spinning blood in a device known as a centrifuge
until the cells collect at the bottom of the tube.
Red blood cells have the important
job of carrying oxygen around the body. They also contain a protein called
hemoglobin. Hemoglobin contains iron which combines with oxygen to give
hemoglobin and our blood, a red color. Red blood cells develop in bone marrow
and circulate in the body for around 120 days. White blood cells are an
important part of the body’s immune system. They defend against certain
bacteria, viruses, cancer cells, infectious diseases and other unwanted
Platelets help blood clot in order
to limit bleeding when your skin is cut. Blood clots can occasionally have
negative effects, if they form in blood vessels going to the brain they can
cause a stroke while clotting in a blood vessel going to the heart which in
turn, can lead to a heart attack. As well as delivering important substances to
our cells, blood also helps take away unwanted waste products.
Grouping human blood types can be a
difficult process and there are currently around 30 recognized blood types (or
blood groups). You might be familiar with the more simplified “ABO” system
which categorizes blood types under O, A, B and AB. Do you know which blood type
Many generous humans around the
world give blood donations every year. This blood is used in important blood
transfusions or made into medication. There are strict rules that limit the
number of people who can volunteer blood donations. These include screening
processes that test for diseases that could be transmitted by a blood
transfusion as well as ensuring recovery time for the donor’s body to replace
its own blood.
One of the principal signs of life
for humans is blood pressure, this is the measure of pressure that circulating
blood has on the walls of blood vessels. Blood pressure is usually taken from a
person’s upper arm. Although averages vary from person to person, a general
human being is known to have a normal blood pressure of around 112/64 mmHg.
A high blood pressure can increase the risk of a stroke or heart attack.