Download BOSY_DEFENCE__ARISTO_

Pathogens


Microorganisms
causing diseases
eg. bacteria
viruses
fungi
protozoa
Importance of having 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
e.g. influenza, cold
 By Touch
e.g. boils, athlete’s foot, AIDS,
anthrax
 By Dust
e.g. diphtheria, scarlet fever,
anthrax, hay 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
Nonspecific
Defences
Barriers
• physical barrier
 Skin
 the 1st line of defence of pathogen
 Ciliated & Mucus Lining of respiratory
tract
 mucus: trap bacteria
 beating cilia: waft the trapped bacteria
towards the throat
Barriers
• chemical barrier
 sebaceous glands of skin
 produce oily secretion (sebum) which has
antiseptic properties
 tears & saliva
 contain lysozymes (enzyme) which
destroy bacteria
Barriers
• chemical barrier
 gastric juice in stomach
 contain acid which can destroy most
bacteria
 acid secretions in vagina of women
 reduce growth of pathogens
When you cut yourself carelessly,
why the wound stop bleeding
after a while ?
∵Blood Clotting occurs:
Platelets release a substance
to turn soluble fibrinogen into
insoluble fibrin which catches
blood cells & seal off the cut
Insoluble
fibrin
BLOOD CLOTTING is important
because this can …
 Prevent the body from invasion of
pathogens
 Stop excess bleeding (blood loss)
Nonspecific
(after infection)
• to localize & destroy the pathogens
• phagocytes involve in phagocytosis
– to engulf and digest the pathogens
macrophage
Nonspecific
(after infection)
• 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 phagocytes & 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
responses will be produced which
involve a series of specific defences
• After pathogens get into the blood & lymph :
• Antigens on the surface of pathogen stimulate
lymphocytes in the lymph nodes and the blood.
–
to produce specific antibodies which kill pathogen
by :
» lysis - burst the pathogen
» clump the pathogen together
• After pathogens get into the blood & lymph :
• Antigens on the surface of pathogen stimulate
lymphocytes
–
to produce specific antibodies which kill pathogen
by :
» stick to the surface of pathogen,
so that phagocytes can ingest
them easily (enhanced phagocytosis)
» neutralize the toxins from pathogens
Primary & Secondary
Immunity Responses
Primary Response: the 1st time
invaded by a certain pathogen which
stimulates the body to produce
antibodies
Primary & Secondary
Immunity Responses
Secondary Response: the invasion of the
same type of pathogen which stimulates
lymphocytes to produce much larger
amount of antibodies & much more quickly
primary
response
secondary
response
antibody
conc.
immune response
no immune response
Time (days)
first exposure
to antigen X
second exposure
to antigen X
Small pox (a killing disease)
Vaccine (Vaccination)
Vaccine (Vaccination)
 From dead / weakened pathogens
– to stimulate the lymphocytes to produce
antibodies
 Times of injection:
– first→ second → (booster) injection
 From injection of a serum
 It belongs to acquired immunity
Injection of a Serum
antibody
conc.
immune response
no immune response
injection of antibody
(in serum)
Time (days)
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