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

 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

Pathogens can be spread :  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:  Saliva contact / droplets (e.g. influenza)  Blood contact (e.g. Hepatitis B)  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:  By vectors ‘insects & other vertebrates like dogs’ (e.g. malaria by mosquito, rabies by dogs)

Body defence Nonspecific DefencesNonspecific Defences Specific DefencesSpecific Defences

Nonspecific Defences 1 st line of defence Barrier Physical Barrier Chemical Barrier Blood clotting Phagocytes Prevent entry Kill pathogens

(1)Skin  Tough outermost layer ‘epidermis’ acts as a mechanical barrier to prevent entry of pathogen Physical /mechanical Barrier

 Hair at entrance/nostril: filter air  Secrete Mucus: trap bacteria  Beating cilia: waft/carry the trapped bacteria towards the throat Physical /mechanical Barrier (2) Ciliated epithelium of respiratory tract

 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 Chemical Barrier

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

BLOOD CLOTTING is important because this can …  Prevent entry of pathogens  Stop bleeding (prevent blood loss)

WBC (Phagocytes) Nonspecific defence (after infection)Nonspecific defence (after infection) WBC engulf & destroy the pathogens by phagocytosis 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 WBC & fluid come into the infected tissues –the skin becomes red & swell up with pain (because of high pressure) Inflammation (infected area becomes red, swollen & painful)

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.

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. What stimulates immune system ?

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 1 st exposure to a certain antigen which stimulates the white blood cell to produce antibodies. or The action in response to the 1st invasion of a certain pathogen 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.

Time (days) antibody conc. primary response secondary response second exposure to antigen X first exposure to antigen X In the 1 st exposure to an antigen, certain WBCs in the body will memorize the antigen. 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.

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)

Time (days) antibody conc. Have immunity no immunity primary response secondary response second exposure to antigen X first exposure to antigen X Threshold valve Disease symptom shown in 1 st exposure, but not in 2nd

Comparison between primary & secondary immune response Primary responseSecondary response ProductionAntibodies, phagocytic WBC & memory WBC Production level & rate Low & slowHigh & fast ImmunityNo, disease symptom shown. Yes, no disease.

How can we acquire immunity? Apart from actual contact,

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. Time (days) injection of antibody (in serum) Have immunity immediate after injection No disease symptom Threshold valve Protection does not last long. Antibodies will be broken down & rejected.

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.

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