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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) ~END~