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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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Blood
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INFOTEXT
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1992-09-04
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Blood is composed of two separate components.
Firstly, there are the blood cells, which
used to be called corpuscles. Blood cells are
either red (which gives blood its colour) or
white, and they have very different
functions. The cells float free in a
yellow-coloured, protein-rich fluid called
plasma. Blood cells (red and white) are
formed in bone marrow. The proteins which
make up plasma are produced in the liver.
Blood has four important functions. The first
of these is to carry oxygen around the body.
Red cells are full of a protein called
haemoglobin, whose function is to carry
oxygen. The haemoglobin molecule is a strong
red colour. The red cells pick up oxygen in
the lungs, and carry it around the body to
where it is needed. The second function is as
a defence against infection, and this is the
function of the white blood cells. There are
several types of white blood cells, but they
all have important roles to play in defending
the body. Some white cells will eat up any
bacteria or foreign material which they come
across. These cells are called phagocytes.
Other white cells (called lymphocytes)
produce special proteins called antibodies,
which stick to invading bacteria and viruses
and label them as foreign, so that they are
attacked by phagocytes and destroyed. Unlike
red cells, which are inert, white cells can
move around by themselves. They are not
confined to the blood, and often patrol
through other tissues such as the skin, to
mop up any invading microbes they may come
across. Damaged or diseased cells in any
organ release chemicals which attract white
cells, which means that they are summoned to
the areas where they are most needed.
Additionally, some of these chemicals
stimulate marrow to produce more white cells,
if the infection is very severe. The third
function is clotting. If a blood vessel is
damaged, blood reacts to form a clot to plug
the hole and prevent more blood leaking out.
Clotting requires special proteins in the
plasma called clotting proteins, and tiny
cell fragments called platelets which are
produced in the bone marrow. Some diseases
and drugs (such as warfarin) affect the
efficiency of clotting, and such people may
lose significant amounts of blood from small
injuries. The last function of the blood is
to carry nutrients around the body. Many
nutrients, such as glucose, are simply
dissolved in the plasma. Others, such as
fatty acids, are carried on plasma proteins
such as albumin. Some special nutrients, such
as iron, are carried on special proteins such
as ferritin. The blood also carries hormones
and other chemical messengers which the body
sends.
Subject by: Dr Aidan M. O'Donnell