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

 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 spreading

Nonspecific Defences

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

 gastric juice in stomach  contain acid which can destroy most bacteria  acid secretions in vagina of women  reduce growth of pathogens chemical barrier Barriers

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

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 (after infection)

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

Time (days) antibody conc. immune response no immune response primary response secondary response second exposure to antigen X first exposure to antigen X

Small pox (a killing disease)

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 immune response no immune response antibody conc. Time (days) injection of antibody (in serum)

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