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Blood is a liquid tissue; it transports substances around the body and
defends it against disease.
The composition and functions of blood
There are a number of links on this page to other pages
in the web. I did not want to re-write these pages so if you want to know more, jump to
the appropriate page. You can do this by clicking the appropriate flag P
or you can use the table at the bottom of this page.
Composition of Blood:
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Red Blood Cells P |
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White Blood Cells P |
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Platelets |
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Plasma which contains: P
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Glucose |
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Amino-acids |
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Vitamins P |
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Hormones P |
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Mineral salts |
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Antibodies |
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Antitoxins |
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Urea |
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Phospholipids |
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Lipoproteins |
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Hydrogencarbonate ions |
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Fibrinogen |
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Blood is a liquid tissue. This means that it contains
cells suspended in a liquid. Red blood cells carry oxygen and help to carry carbon
dioxide. White blood cells are involved in the body's defense mechanisms. Platelets are
fragments of cells; they help blood to clot.. The liquid is called plasma. It contains
many important substances which must be carried around the body.
There are about five million red blood cells in one
cubic millimetre of blood, perhaps a bit more in boys and less in girls. If you are
accessing this page from high altitude and you have lived up in the mountains for years,
there will be many more red blood cells in your blood, possibly seven million.
Functions:
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Transport of:
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The products of digestion P |
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Respiratory gases P |
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Hormones P |
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Vitamins P |
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Urea |
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Heat |
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Defense:
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Production of antibodies and antitoxins |
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Phagocytosis of "germs" |
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Clotting |
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Antibodies kill bacteria. You may have a natural immunity to some
diseases, but other diseases are likely to kill you if you do not receive medical
attention. The problem is that the germs multiply faster than you white blood cells kill
them. If you cannot make the right antibodies you will get very ill and could die. You can
teach your body to recognise diseases like smallpox by "inoculating" yourself (get
your doctor to do it) with a very similar disease like cowpox. Edward Jenner discovered
this. Cowpox does not make you very ill and will certainly not kill you. When your white
blood cells have learnt how to make the antibodies needed to destroy cowpox they can also
destroy smallpox. Get yourself inoculated now especially if you are going to a part of the
world where smallpox is endemic.
When you cut yourself, the damaged blood vessels trigger the
clotting process. Fibrinogen, which is a soluble protein in your blood, turns into fibrin
which is an insoluble fibrous protein. Platelets get caught in the network of fibrin and
form a clot which dries up into a scab. This is quite a good thing because it prevents any
more blood from getting out and it prevents germs from getting in.
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