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Wednesday, May 3, 2017
Defence Against Disease
 To understand how the body defends itself against disease
Pathogen Barriers
 Complete the pathogen barriers
worksheet
Pathogen Barriers
Wax traps microorganisms
Tears contain an enzyme
which kills microorganisms
Hairs and mucus stop
micro-organisms from
entering the body
Saliva contains an
enzyme which kills microorganisms
Blood contains white
blood cells which kill any
micro-organisms within
the body
Skin barrier stops microorganisms from entering
the body
Defence
 How does our body defend us from micro-organisms?
The skin acts as a
barrier
If our skin is cut
platelets seal the
wound by clotting
The breathing organs
produce mucus to cover the
lining of these organs and
trap the microbes
Our blood contains
white blood cells
Passive & Active Defence
 The body has different ways of protecting itself against pathogens
 The first defence is passive immunity – aimed at stopping the
pathogen getting into the body in the first place
 The body’s passive immunity system includes:  Skin
 Mucus and cilia (tiny hairs) in the respiratory system
 Acid in the stomach
 Enzymes in tears
 If a pathogen still manages to get into the body, the second
defence takes over – this is called active immunity, and the white
blood cells have key functions in this…
Bacterial Investigation
 Complete the bacterial
investigation…
White Blood Cells
 White blood cells can:  Ingest pathogens and destroy them
 Produce antibodies to destroy pathogens
 Produce antitoxins that neutralise the toxins released by
pathogens
 Pathogens are not the disease – they cause the disease!
 White blood cells ingest pathogens (they do
not eat them!)
White Blood Cells
 There are several different types of white blood cells, each with
different functions, but they can be put into two main groups:  Phagocytes or macrophages
 Lymphocytes
Phagocytes
 Phagocytes can easily pass through blood vessel walls into the
surrounding tissue and move towards pathogens or toxins
 They then either ingest and absorb the pathogens or toxin; or
release an enzyme to destroy them
 Having absorbed a pathogen, the phagocytes may also send out
chemical messages that help nearby lymphocytes to identify the
type of antibody needed to neutralise them
Phagocytes
Lymphocytes
 Pathogens contain certain chemicals that are foreign to the body
and are called antigens
 Each lymphocyte carries a specific type of antibody - a protein
that has a chemical 'fit' to a certain antigen
 When a lymphocyte with the appropriate antibody meets the
antigen, the lymphocyte reproduces quickly, and makes many
copies of the antibody that neutralises the pathogen
Antibodies attach
White blood cell
Pathogen
(coated in antigens)
Lymphocytes
Antibodies
 Antibodies neutralise pathogens in a number of ways: 1.
They bind to pathogens and damage or destroy them
1.
They coat pathogens, clumping them together so that they are
easily ingested by phagocytes
1.
They bind to the pathogens and release chemical signals to
attract more phagocytes
 Lymphocytes may also release antitoxins that stick to the
appropriate toxin stopping it damaging the body
Antibodies
Step 1 – the white blood cell
identifies the pathogen
Step 2 – antibodies produced
to ‘fit’ the pathogen
Step 3 – antibodies fit the
pathogen, ‘clumping’ them
Step 4 – the white blood cell
ingests the pathogen
Antibodies
Fighting Diseases
 Natural immunity – antibodies are produced by a person when
needed or they are passed on by the mother during pregnancy
 Artificial immunity – a vaccine with dead microbes is injected
tricking the body into producing antibodies ready for the real
thing
Vaccinations & Immunisation
 Vaccination – taking a vaccine as a precaution against a disease
 Immunisation – making an animal resistant (immune) to a disease
by taking a vaccine
Vaccination
 People can be immunised against a pathogen through vaccination
 Vaccination involves putting a small amount of an inactive form
of a pathogen, or dead pathogen, into the body
 Vaccines can contain:  Live pathogens (treated to make them harmless)
 Harmless fragments of the pathogen
 Toxins produced by pathogens
 Dead pathogens
 These all act as antigens – when injected into the body, they
stimulate white blood cells to produce antibodies against the
pathogen
Vaccination
 Because the vaccine contains only a weakened or harmless version
of a pathogen, the vaccinated person is not in danger of
developing disease - although some people may suffer a mild
reaction
 If the person does get infected by the pathogen later, the required
lymphocytes are able to reproduce rapidly and destroy it
Boosters
 Vaccines in early childhood can give protection against many
serious diseases
 Sometimes more than one vaccine is given at a time, like the
MMR triple vaccine against mumps, measles and rubella
 Sometimes vaccine boosters are needed, because the immune
response 'memory' weakens over time (anti-tetanus injections may
need to be repeated every ten years)
Vaccine Example
 Complete a cartoon strip to show how a vaccine works…
 The discuss the pros / cons of vaccines within your groups
Vaccine
 A preparation of dead or weakened pathogens, that is used to
induce formation of antibodies or immunity against the pathogen
Real pathogen
for disease
Vaccine for disease
( a weakened version)
Vaccine
 Vaccine (pathogen) injected into the bloodstream
Injection
Vaccine
 Vaccine enters the blood stream
skin
Vaccine (pathogen)
Blood vessel
White blood cells
Red blood cells
Vaccine
 White blood cells detect a foreign body and surround it
Vaccine
 White blood cells make antibody against the vaccine (pathogen)
Antibody – this is specific to this
particular vaccine (pathogen)
Vaccine
 The antibody acts as a marker for other white blood cells to come
along and engulf the vaccine (pathogen)
White blood cells that
destroy pathogens
Vaccine
 The vaccine (pathogen) has been destroyed and the antibody is left
in the blood stream (active immunity)
 *In passive immunity the body is actually given the antibodies –
this only lasts at most a few years
Vaccine Pros & Cons
Pros
Cons
Protection against disease
Some side effects, e.g. bruising
Protection against more serious damage
e.g. brain damage and death
Discomfort for young children
Reduces chances of an epidemic
Some health concerns (MMR and autism
link (dismissed))
It is cheaper to give a vaccine than treat an
infected patient
Reduces hospital load
MMR is 3 immunisations in 1
MMR Controversy
 Research the measles, mumps rubella (MMR) vaccination
controversy – was there any scientifically significant link between the
MMR jab and autism…
 How did Andrew Wakefield collect the data, and should he
have conducted the study?
 Was 12 individuals enough to warrant the study?
 How should he have collected the data, and how much data
should he have taken?
 What long term problems has this study caused?