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PathogensPathogens Microorganisms c
ausing diseases eg. bacteria
viruses fungi protozoa
Importance of having Importance of having Body Defense SystemBody Defense System
prevent pathogens from entering the body
kill or inactivate any pathogens that gain entry into the body
Ways of Pathogen Ways of Pathogen spreading 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
In Faeces e.g. cholera, hepatitis A
In Food e.g. salmonella
By Insect e.g. malaria
By Vertebrates e.g. rabies
Ways of Pathogen Ways of Pathogen spreading spreading
Nonspecific Nonspecific DefencesDefences
• 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
BarriersBarriers
• chemical barrier sebaceous glands of skin produce oily secretion (sebum) whic
h has antiseptic properties tears & saliva contain lysozymes (enzyme) which d
estroy bacteria
BarriersBarriers
gastric juice in stomach contain acid which can destroy
most bacteriaacid secretions in vagina of
womenreduce growth of pathogens
• chemical barrier
BarriersBarriers
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
Insolublefibrin
BLOOD CLOTTINGBLOOD CLOTTING is is important because this important because this can …can … Prevent the body from
invasion of pathogens
Stop excess bleeding (blood loss)
Nonspecific Nonspecific (after (after
infection)infection)• to localize & destroy the pathogens• phagocytes involve in phagocytosis
– to engulf and digest the pathogens
macrophage
• 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)
Nonspecific Nonspecific (after (after
infection)infection)
Specific Specific DefencesDefences
What are Specific What are Specific Defences ?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 & Primary & Secondary Secondary Immunity Immunity ResponsesResponses
Primary Response: the 1st
time invaded by a certain
pathogen which stimulates
the body to produce
antibodies
Primary & Primary & Secondary Secondary Immunity Immunity ResponsesResponses
Secondary Response: the invasion
of the same type of pathogen
which stimulates lymphocytes to
produce much larger amount of
antibodies & much more quickly
Time (days)
antibodyconc.
immune response
no immune response
primaryresponse
secondaryresponse
second exposureto antigen X
first exposureto antigen X
Small pox (a killing disease)
Vaccine Vaccine (Vaccination)(Vaccination)
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 SerumInjection of a Serum
immune response
no immune response
antibodyconc.
Time (days)injection of antibody
(in serum)
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