20 Defence against diseases

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20 Defence against diseases

• 20.1 What is a disease?
• 20.2 Body defence
• 20.3 Non-specific defences
• 20.4 Specific defences
• 20.5 Immunity and vaccination
• Mind Map

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20.1 What is a disease?
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20.1 What is a disease?
Diseases
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20.1 What is a disease?
Types
Diseases
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20.1 What is a disease?
Non-infectious diseases
Disease cannot be spread
e.g. diabetes mellitus, arthritis, cancer
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20.1 What is a disease?
Disease can be spread
Infectious diseases
e.g. cholera, hepatitis A
Generally caused by microorganisms called
pathogens (germs)
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20.1 What is a disease?
Pathogens
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20.2 Body defence
Body Defence
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20.2 Body defence
Body
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No entry
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20.2 Body defence
Body
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No entry
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Kill or inactivate
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20.2 Body defence
Three lines of body defence
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20.3 Non-specific defences
Non-specific
defences
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20.3 Non-specific defences
Physical Barrier
Physical Barrier
Chemical Barrier
Phagocytes
Blood Clotting
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20.3 Non-specific defences
Physical Barrier
germs
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20.3 Non-specific defences
Physical Barrier
traps bacteria
waft the trapped particles towards the throat
the mucus is then swallowed or expelled
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20.3 Non-specific defences
Physical Barrier
Chemical Barrier
Chemical Barrier
Phagocytes
Blood Clotting
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20.3 Non-specific defences
Chemical Barrier
Sebaceous glands produce sebum
Sebum (an oily secretion)
contains a chemical which kills pathogens on the
skin
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20.3 Non-specific defences
Chemical Barrier
Tears contain lysozymes
Saliva also contains lysozymes
Lysozyme destroys bacteria by digesting their
cell walls
Tears wash away pathogens and dust particles
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20.3 Non-specific defences
Chemical Barrier
Stomach secretes acidic gastric juice
Gastric juice can kill most of the bacteria
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20.3 Non-specific defences
Chemical Barrier
Vagina produces acidic secretion
Acidic secretion of the vagina inhibits the
growth of pathogens
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20.3 Non-specific defences
Physical Barrier
Chemical Barrier
Phagocytes
Phagocytes
Blood Clotting
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20.3 Non-specific defences
Phagocyte digests the bacteria
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Phagocyte engulfs the bacteria
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bacteria
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squeezes out of capillary wall
by amoeboid movement
Dilation of arterioles
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brings more blood to infected area
Inflammation
Capillary wall becomes more permeable
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20.3 Non-specific defences
Physical Barrier
Chemical Barrier
Phagocytes
Blood Clotting
Blood Clotting
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20.3 Non-specific defences
Blood Clotting
Protects the body from invasion by pathogens
Stops further bleeding
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20.4 Specific defences
Specific
defences
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20.4 Specific defences
If a pathogen is able to get past
the bodys non-specific defences
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20.4 Specific defences
white blood cells
Perform phagocytosis to kill pathogens
Produce antibodies to kill pathogens
Non-specific response
Specific response
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20.4 Specific defences
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20.4 Specific defences
Antibodies
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They are produced by lymphocytes
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Their functions is to remove antigens
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Their actions are specific
i.e. a kind of antibodies only attacks its
corresponding antigen
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20.4 Specific defences
How do antibodies work?
1. Attach the surface of the antigen
3. The pathogen bursts
2. Make holes on the wall of the pathogens
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20.4 Specific defences
How do antibodies work?
2. Phagocyte can engulf the bacterium more easily
1. Attach to the surface of the pathogen
3. The pathogen is killed by the phagocyte
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20.4 Specific defences
How do antibodies work?
Cause the pathogens to clump together
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20.4 Specific defences
How do antibodies work?
antitoxin
Combines directly with toxins secreted by bacteria
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20.4 Specific defences
Primary
Secondary
Immune Response
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20.4 Specific defences
Antibody concentration
Time (days)
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20.4 Specific defences
There is no antibody production until day 7
because the rate of production
of antibodies is very slow
Antibody concentration
Time (days)
1st exposure to antigen X
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20.4 Specific defences
After day 17, the rate of production of
antibodies is decreasing
Antibody concentration
because the amount of antigens is decreasing
Time (days)
1st exposure to antigen X
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20.4 Specific defences
When the body is exposed to the same antigen again
Antibody concentration
Time (days)
1st exposure to antigen X
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20.4 Specific defences
Antibody concentration
Why the secondary response is different from the
primary one ?
Time (days)
1st exposure to antigen X
2nd exposure to antigen X
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20.4 Specific defences
After the primary response
When the body is exposed to the same antigen again
This response is called secondary response
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20.5 Immunity and vaccination
Immunity
Vaccination
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20.5 Immunity and vaccination
Immunity
If the same antigen re-enters the body again
The readiness of the body to resist disease in
this way is called immunity
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20.5 Immunity and vaccination
Acquired Immunity
If a persons immunity is acquired by actual
contact with the antigen
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20.5 Immunity and vaccination
Acquired Immunity
achieved by infection
achieved by vaccination or injection of a serum
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20.5 Immunity and vaccination
Vaccination
We can be immunised against a disease by
receiving a vaccine
Dead or weakened pathogens
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20.5 Immunity and vaccination
Primary response
After vaccine is injected
some white blood cells memorise the antigen
Subsequent exposure to the same type of antigen
the white blood cells will take
the response to produce a large
amount of specific antibodies quickly
Secondary response
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20.5 Immunity and vaccination
Vaccination programme is set up by the Health
Department in HK
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20.5 Immunity and vaccination
contains antibodies
Injection of serum
After injection of serum,
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20.5 Immunity and vaccination
contains antibodies
Injection of serum
High antibody level does not last long
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20.5 Immunity and vaccination
Summary
immediate immunity
slower immunity
short-lived
long-lived
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Mind Map
readiness of body to resist disease
Body defence
can be divided into
against

non-specific defences

specific defences
diseases
immunity
include
are
include
can be achieved artificially by

1. physical barrier

immune responses

1. infectious diseases
1. vaccination

2. chemical barrier
involve the production of

2. injection of serum
include

2. non-infectious diseases
3. phagocytes
antibodies

4. blood clotting
by
lymphocytes

primary immune responses

secondary immune responses
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