Transcript Body Defence

Body Defence
Prepared by Ms W.S.Kwan
Pathogens


Microorganisms
causing diseases
eg. bacteria
viruses
fungi
protozoa
Pathogens cause diseases
• By direct attack, destroying the cell &/or
• By releasing toxins, which upset our internal
environment
• Diseases caused pathogens are called infectious
diseases
Body Defense System
 prevent pathogens from entering
the body
 kill or inactivate any pathogens
that gain entry into the body
Ways of Pathogen spreading
 In Droplets / saliva & sneeze
e.g. influenza, cold
 By Touch
e.g. boils, athlete’s foot, AID
 By Dust
e.g. diphtheria, scarlet fever
Ways of Pathogen spreading
 In Faeces
e.g. cholera, hepatitis A
 In Food
e.g. salmonella
 By Insect
e.g. malaria
 By Vertebrates
e.g. rabies
Pathogens can be spread:
L By ingestion of contaminated food or water (e.g.
salmonella, cholera & Hepatitis A)
Pathogens are common in faeces & water.
Pathogens can be spread:
• By inhalation of dust with pathogens / airborne
pathogens
Pathogens can be spread:
• By body fluid contact:
• L Saliva contact / droplets
(e.g. influenza)
• L Blood contact
(e.g. Hepatitis B)
• L Sexual contact
(e.g. Hepatitis B)
Pathogens can be spread:
By direct contact with an infected area (e.g. athlete’s foot)
Pathogens can be spread:
L
By vectors ‘insects & other vertebrates like dogs’
(e.g. malaria by mosquito, rabies by dogs)
Body defence
• Nonspecific Defences
• Specific Defences
Nonspecific Defences
st
1 line of defence
• Barrier
Physical Barrier Prevent entry
Chemical Barrier Kill pathogens
• Blood clotting Prevent entry
• Phagocytes Kill pathogens
Physical /mechanical Barrier
(1) Skin
Tough outermost layer
‘epidermis’ acts as a mechanical
barrier to prevent entry of
pathogen
Physical /mechanical Barrier
(2) Ciliated epithelium of respiratory tract
 Hair at entrance/nostril: filter air
 Secrete Mucus: trap bacteria
 Beating cilia: waft/carry the trapped
bacteria towards the throat
Chemical Barrier
 Sebaceous glands of skin
 Produce oily secretion (sebum)
which has antiseptic properties
 Tears & saliva
 Contain lysozymes (enzyme) which
destroy bacteria
Chemical Barrier
Gastric juice in stomach
Contain acid which can destroy
most bacteria
Acid secretions in vagina of women
reduce growth of pathogens
Blood clotting
When exposed to
air in wound, blood
platelets release a
substance to turn
soluble fibrinogen
into insoluble fibrin
which catches blood
cells & seal off the
cut.
BLOOD CLOTTING is important
because this can …
 Prevent entry of pathogens
 Stop bleeding (prevent blood loss)
WBC (Phagocytes)
• Nonspecific defence (after infection)
• WBC engulf & destroy the pathogens
by phagocytosis
macrophage
Inflammation
(infected area becomes
red, swollen & painful)
• inflammatory response
– (before inflammation : skin arterioles
constrict to prevent excessive bleeding)
– skin arterioles in the infected area dilates so
that more blood flows to the area
– the permeability of skin capillaries
increases so that more WBC & fluid come
into the infected tissues
– the skin becomes red & swell up with pain
(because of high pressure)
Specific
Defences
What are Specific Defences ?
• When a pathogen is able to get past
the nonspecific defences,
• immune system will produce a series
of immune responses to attack the
pathogen.
• These immune responses are the
specific defences of our body.
What stimulates immune system ?
• After pathogens get into the blood &
lymph,
• Antigens on the surface of pathogen
stimulate WBC (lymphocytes) to produce
specific antibodies
Note: Antibodies are specific & protein in nature.
How antibodies kill pathogens?
lysis - burst the pathogen
clump the pathogen together
stick to pathogen
(enhanced phagocytosis)
neutralize the toxins from
pathogens
Primary (immune) Responses
The action in response to the 1st invasion of
a certain pathogen which stimulates the
white blood cell to produce antibodies.
st exposure
The
action
in
response
to
the
1
or
to a certain antigen which stimulates the
white blood cell to produce antibodies.
Secondary (immune) Responses
The action in response to the 2nd invasion
of the same type of pathogen which
stimulates the white blood cell to produce
much more quickly & much larger amount
of antibodies specific the antigen.
primary
response
secondary
response
In the 1st exposure to an antigen,
certain WBCs in the body will
memorize the antigen.
antibody
conc.
In subsequent exposures to the same
antigen, the memory WBCs will
multiply immediately to produce
large amount of phagocytic WBC &
antibodies specific to the antigen.
Time (days)
first exposure
to antigen X
second exposure
to antigen X
Immunity
• Immunity means
Body is able to resist the disease
• Once the body has the threshold
amount of antibodies, the body can
resist the disease (i.e. Immunity)
Disease symptom shown in 1st exposure, but not in 2nd
primary
response
secondary
response
antibody
conc.
Have immunity
Threshold
valve
no immunity
Time (days)
first exposure
to antigen X
second exposure
to antigen X
Comparison between primary &
secondary immune response
Production
Production
level & rate
Immunity
Primary response
Secondary response
Antibodies,
phagocytic WBC &
memory WBC
Low & slow
Antibodies,
phagocytic WBC &
memory WBC
High & fast
No, disease symptom
shown.
Yes, no disease.
Apart from actual contact,
How can we acquire immunity?
Vaccine story
• In 1771 in England,
smallpox
widespread.
• Have cowpox, no
smallpox.
• Experiment on a
boy.
Vaccination
 Vaccine
= dead / weakened pathogens
To stimulate the WBC to produce antibodies
 Vaccine
taken:
By injection, skin scratching or mouth (orally)
 Times
of taken:
First→ second → (booster) to get full immunity
 Vaccination
is a form of artificial immunity.
Principles of vaccination:
• A previous exposure of the body to an
antigen will be memorized by certain
type of white blood cell in the body.
• Subsequent exposure to the same type of
antigen will initiate a rapid production of
a large amount of phagocytic white blood
cells & antibodies specific for that
antigen.
Injection of a Serum
antibody
conc.
Have immunity immediate after injection
No disease symptom
Threshold
valve
Protection does not last
long. Antibodies will be
broken down & rejected.
injection of antibody
(in serum)
Time (days)
Pupils should be able to:
1. Explain the function of the skin as mechanical barrier against
bacteria.
2. Describe the action of the ciliated epithelium of the respiratory
tract in filtering dust particles & bacteria from air.
3. State that hydrochloric acid in the gastric juice kills most
bacteria in the food reaching the stomach.
4. State that the blood clot covers the wound to stop bleeding &
to prevent entry of pathogens.
5. State that white blood cells can protect our body by engulfing
bacteria & producing antibodies.
Pupils should be able to:
6. Explain the principles of vaccination, a form of
artificial immunity, including:
(a) A previous exposure of the body to an antigen will be
memorized by certain type of white blood cell in the
body.
(b) Subsequent exposure to the same type of antigen will
initiate a rapid production of a large amount of
phagocytic white blood cells & antibodies specific for
that antigen.
~END~