Chapter 10
By the end of this lesson we will be able to:
 Explain what is a pathogen.
 Describe how pathogens can be transmitted through direct
contact, or indirectly.
 Describe how the skin, hairs in the nose, mucus, stomach
acid and white blood cells help to defend against pathogen.
 Explain the importance of clean water, hygienic food
preparation, personal hygiene, waste disposal and sewage
treatment in controlling the spread of disease.
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Pathogen:
Is a microorganism that causes disease. Very tiny organisms
that can only seen with a microscope.
Many pathogens enter our bodies and breed there. Some
pathogens damage our cells either by:
1.
living in them and using up their resources.
2.
Producing waste products, called toxin (poisonous
substance; chemical that damages cell) which spread
around the body and cause symptoms (features that you
experience when you have a disease), such as high
temperature and rash and make you feel ill.
Toxin produced by the bacterium Clostridium botulinum is one
of the most dangerous poisons in the world.
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a.
b.
the movement of a pathogen from one host to another is
called: transmission.
The entry of pathogen into the body is known as infection.
There are several ways in which transmission and infection
can happen:
By direct contact, including through blood and other body
fluids, like AIDS.
Indirectly, including from contaminated surfaces, food
(Salmonella), water( poliomyelitis and cholera), animals and
air, like cold, covid-19.
Transmissible Diseases (contagious): diseases in which the
pathogen can be passed from one host to another.
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The human body has many natural defences against
pathogens.
Some prevent pathogens from getting in the body.
In they enter, white blood cells destroy them either by
phagocytosis or production of antibodies.
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A clean water supply.
Hygienic food preparation.
Good personal hygiene.
Waste disposal.
Sewage treament
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It is a serious transmissible disease caused by a bacterium
called: Vibrio cholera.
it can be spread through contaminated water and food with
faeces from an infected person.
Cholera bacteria live and breed in small intestine, and
produce a toxin (poison).
Toxin stimulates the cells lining the small intestine to
secrete chloride ions.
These chloride ions accumulate in the lumen of the small
intestine.
This increases the concentration of the fluid in the lumen,
lowering its water potential.
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Once water potential becomes lower than the water
potential of the blood flowing through the vessels in the
walls of intestine, water moves out of the blood and into
the lumen of intestine by osmosis.
The infected person suffers sever diarrhoea, in which large
quantities of water are lost from the body in watery faeces.
Without treatment, death may occur from dehydration and
loss of chloride ions from the blood.
Enough fluids can be given to replace these losses.