Transcript 11.4 defence against diseases

Defence against disease
Microorganisms that cause infectious disease are called
pathogens.
Which Pathogens can you name?
These are “Rod – shaped” Bacteria on the end of a pin.
Viruses are much smaller than bacteria. They invade
body cells and then hijack the cells DNA to reproduce.
They can cause lots of damage to cells.
Bacteria, Viruses and Fungi are all Pathogens.
Bacteria and viruses may reproduce rapidly inside
the body and may produce poisons (toxins) which
make us feel ill.
Viruses damage cells in which they reproduce.
• The body has different ways of protecting itself
against pathogens. White blood cells help to defend
against pathogens:
− by ingesting pathogens
− by producing antibodies which destroy particular
bacteria or viruses
− by producing antitoxins which counteract the toxins
(poisons) released
Ingesting Pathogens
White Blood Cell approaches
pathogen
Pathogen
White Blood Cell
White Blood Cell stretches
to form a bubble around the
pathogen.
White Blood Cell releases
enzymes to digest the
pathogen.
The process is complete.
Producing Antibodies
Producing Antitoxins
Bacteria
The bacteria
produces toxins
White Blood Cell
The White Blood Cell
produces antitoxins to
neutralise the toxins.
Other causes of Disease
• Genetic causes – inherited from parents
• Parasitic - you can catch an organism
that causes a disease –
e.g. malaria – protozoa,
thread worm
crab lice
Immunisation
People can be immunised against a disease by introducing
small quantities of dead or inactive forms of the pathogen
into the body (vaccination).
Vaccines stimulate the white blood cells to produce
antibodies that destroy the pathogens.
This makes the person immune to future infections by the
microorganism, because the body can respond by rapidly
making the correct antibody, in the same way as if the
person had previously had the disease.
An example is the MMR vaccine used to protect children
against measles, mumps and rubella.
The first vaccine was against a virus called small pox.
Small pox is a dreadful disease that killed hundreds of
thousands of people especially children. Those it did not
kill were usually horribly scarred.
In the nineteenth century Edward Jenner noticed that
cow maids often caught cow pox, a less dangerous form
of small pox. If the cow maids ever caught small pox
they recovered quickly and with not many complications.
Jenner came up with a theory that if someone was
deliberately infected with cow pox then they would be
immune to small pox.
What Jenner did next has caused
much debate in science. Jenner
took a sample of cow pox from a
milk maid and using a needle put it
into his son. His son duly caught
cow pox and recovered.
That may sound a bit cruel but
what Jenner did next was worse he
took a sample of the deadly small
pox and using the same method
injected that into his son as well.
Jenner was lucky his son lived and
proved his theory correct.