Download What is a Disease?

20 Defence against diseases
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20.1 What is a disease?
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20.2 Body defence
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20.3 Non-specific defences
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20.4 Specific defences
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20.5 Immunity and vaccination
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Mind Map
20.1 What is a disease?
20.1 What is a disease?
Diseases
any condition
prevents the
body, or part of it,
from working
properly
feeling ill is a
symptom of a
disease
20.1 What is a disease?
Types
Diseases
Non-infectious
diseases
Infectious
diseases
20.1 What is a disease?
Non-infectious
diseases
Disease
cannot be
spread
e.g. diabetes
mellitus, arthritis,
cancer
20.1 What is a disease?
Infectious
diseases
Disease can
be spread
e.g. cholera,
hepatitis A
Generally caused
by
microorganisms
called pathogens
(germs)
20.1 What is a disease?
Pathogens
1. bacteria
2. viruses
4. protoctists
3. fungi
20.2 Body defence
20.2 Body defence
1 Germ
No entry
Germ
Germ
Germ
Germ
Body
20.2 Body defence
1
Germ
Germ
No entry
Germ
Body
Germ
2
Kill or
3
inactivate
20.2 Body defence
1st line
Three lines
of body
defence
2nd
line
Last line
by natural
barriers
Non-specific
defence
by white
blood cells
by immune
system
Specific
defence
20.3 Non-specific defences
20.3 Non-specific defences
20.3 Non-specific defences
1
Skin
germs
Prevents
the entry of
pathogens
outermost
layer
epidermis
sebaceous
gland
20.3 Non-specific defences
2
traps bacteria
Mucus
Ciliated lining of the
respiratory tract
Beating cilia
waft the trapped
particles towards
the throat
the mucus is then
swallowed or
expelled
20.3 Non-specific defences
20.3 Non-specific defences
Sebaceous glands
produce sebum
Sebum
(an oily secretion)
contains a chemical
which kills pathogens
on the skin
20.3 Non-specific defences
Tears contain
lysozymes
Lysozyme
destroys bacteria
by digesting their
cell walls
Tears wash away
pathogens and
dust particles
Saliva also
contains
lysozymes
20.3 Non-specific defences
Stomach secretes
acidic gastric
juice
Gastric juice
can kill most
of the bacteria
20.3 Non-specific defences
Vagina produces
acidic secretion
Acidic secretion
of the vagina
inhibits the growth
of pathogens
20.3 Non-specific defences
20.3 Non-specific defences
3 Phagocyte
bacteria
engulfs the
bacteria
phagocyte
4
Phagocyte
digests the
bacteria
2
squeezes out of capillary wall
by amoeboid movement
capillary
Dilation of arterioles
1
Inflammation
brings more blood to
infected area
Capillary wall becomes
more permeable
20.3 Non-specific defences
20.3 Non-specific defences
red blood cells
trapped in a
network of fibrin
threads
platelet plug
Protects the
body from
invasion by
pathogens
Stops further
bleeding
20.4 Specific defences
20.4 Specific defences
If a pathogen is able to get past
the body’s non-specific defences
the immune system will start off
a series of specific defences
that attack the pathogens
These are called
immune responses
20.4 Specific defences
white
blood
cells
Phagocytes
Lymphocytes
Perform
phagocytosis to
kill pathogens
Produce
antibodies to
kill pathogens
Non-specific
response
Specific
response
20.4 Specific defences
antigen
stimulates
Lymphocytes
bacterium
to
produce
antibodies
20.4 Specific defences
Antibodies
1
They are produced by lymphocytes
2
3
Their functions is to remove antigens
Their actions are specific
i.e. a kind of antibodies only attacks
its corresponding antigen
20.4 Specific defences
How do antibodies work?
1. Attach the
surface of the
antigen
bacterium
3. The
pathogen
bursts
antigen
bacterium
bacterium
antibody
2. Make
holes on the
wall of the
pathogens
20.4 Specific defences
How do antibodies work?
antibody
bacterium
1. Attach to
the surface of
the pathogen
2. Phagocyte
can engulf
the
bacterium
more easily
3. The
pathogen is
killed by the
phagocyte
20.4 Specific defences
How do antibodies work?
Cause the
pathogens to
clump
together
Lower their
harmful
activities
antibody
antigen on
pathogen
20.4 Specific defences
How do antibodies work?
Combines
directly with
toxins secreted
by bacteria
make them
harmless
antitoxin
toxin
antibody
20.4 Specific defences
Primary
Secondar
y
Antibody concentration
20.4 Specific defences
1st
exposure
to antigen X
Time (days)
20.4 Specific defences
Antibody concentration
There is no antibody production until day 7
1st
because the rate of production
of antibodies is very slow
This period is called
latent period
*
*
exposure
to antigen X
Time (days)
20.4 Specific defences
Antibody concentration
After day 17, the rate of production of
antibodies is decreasing
1st
because the amount of antigens is decreasing
exposure
to antigen X
Time (days)
20.4 Specific defences
Antibody concentration
When the body is exposed to the same antigen again
1st
3
The amount of
antibodies is very
large
1
Latent period is
very short
exposure
to antigen X
2nd
2
The rate of
production of
antibodies is very
fast
exposure
to antigen X
Time (days)
20.4 Specific defences
Antibody concentration
Primary
response
1st
Secondary
response
Why the secondary response is
different from the primary one ?
exposure
to antigen X
2nd
exposure
to antigen X
Time (days)
20.4 Specific defences
After the primary response
Some white blood cells
memorise the antigen
1
When the body is exposed
to the same antigen again
a much larger amount of phagocytes
and antibodies is produced
2
in a shorter time
This response is called secondary response
20.5 Immunity and vaccination
20.5 Immunity and vaccination
Immunity
If the same antigen re-enters the body again
the body can produce a large
amount of antibodies quickly
antibody level becomes high enough to
give protection against pathogen
The readiness of the body to resist
disease in this way is called immunity
20.5 Immunity and vaccination
Acquired Immunity
If a person’s immunity is acquired
by actual contact with the antigen
It is known as
acquired immunity
20.5 Immunity and vaccination
Acquired Immunity
Natural
immunity
achieved by
infection
Artificial
immunity
achieved by
vaccination or
injection of a serum
20.5 Immunity and vaccination
Vaccination
We can be immunised
against a disease
by receiving a vaccine
This process is called
vaccination
Dead or
weakened
pathogen
s
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
20.5 Immunity and vaccination
Vaccination programme is set up by the
Health Department in HK
Measles
Rubella
Viral
Poliomyelitis
hepatitis B
Tetanus
Mumps
Diphtheria
Whooping
cough
20.5 Immunity and vaccination
Injection of serum
contains
antibodies
antibody level
After injection
of serum,
injection of serum
antibodies will
be immediately
available to limit
the development
of disease
20.5 Immunity and vaccination
Injection of serum
contains
antibodies
antibody level
High antibody level
does not last long
injection of serum
because the
antibodies will be
broken down and
rejected
20.5 Immunity and vaccination
Serum injection
Vaccination
immediate
immunity
slower
immunity
short-lived
long-lived
Mind Map
Body defence
readiness of body to resist disease
can be
divided into
against
non-specific
defences
diseases
specific
defences
include
include
1. infectious
diseases
2. non-infectious
diseases
are
1. physical
barrier
immune
responses
2. chemical
barrier
include
3. phagocytes
involve the
production
of
antibodies
4. blood
clotting
by
lymphocytes
secondary
immune
responses
primary
immune
responses
immunity
can be achieved
artificially by
1. vaccination
2. injection of
serum