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20 Defence against diseases • 20.1 What is a disease? • 20.2 Body defence • 20.3 Non-specific defences • 20.4 Specific defences • 20.5 Immunity and vaccination • Mind Map 20.1 What is a disease? 20.1 What is a disease? Diseases any condition prevents the body, or part of it, from working properly feeling ill is a symptom of a disease 20.1 What is a disease? Types Diseases Non-infectious diseases Infectious diseases 20.1 What is a disease? Non-infectious diseases Disease cannot be spread e.g. diabetes mellitus, arthritis, cancer 20.1 What is a disease? Infectious diseases Disease can be spread e.g. cholera, hepatitis A Generally caused by microorganisms called pathogens (germs) 20.1 What is a disease? Pathogens 1. bacteria 2. viruses 4. protoctists 3. fungi 20.2 Body defence 20.2 Body defence 1 Germ No entry Germ Germ Germ Germ Body 20.2 Body defence 1 Germ Germ No entry Germ Body Germ 2 Kill or 3 inactivate 20.2 Body defence 1st line Three lines of body defence 2nd line Last line by natural barriers Non-specific defence by white blood cells by immune system Specific defence 20.3 Non-specific defences 20.3 Non-specific defences 20.3 Non-specific defences 1 Skin germs Prevents the entry of pathogens outermost layer epidermis sebaceous gland 20.3 Non-specific defences 2 traps bacteria Mucus Ciliated lining of the respiratory tract Beating cilia waft the trapped particles towards the throat the mucus is then swallowed or expelled 20.3 Non-specific defences 20.3 Non-specific defences Sebaceous glands produce sebum Sebum (an oily secretion) contains a chemical which kills pathogens on the skin 20.3 Non-specific defences Tears contain lysozymes Lysozyme destroys bacteria by digesting their cell walls Tears wash away pathogens and dust particles Saliva also contains lysozymes 20.3 Non-specific defences Stomach secretes acidic gastric juice Gastric juice can kill most of the bacteria 20.3 Non-specific defences Vagina produces acidic secretion Acidic secretion of the vagina inhibits the growth of pathogens 20.3 Non-specific defences 20.3 Non-specific defences 3 Phagocyte bacteria engulfs the bacteria phagocyte 4 Phagocyte digests the bacteria 2 squeezes out of capillary wall by amoeboid movement capillary Dilation of arterioles 1 Inflammation brings more blood to infected area Capillary wall becomes more permeable 20.3 Non-specific defences 20.3 Non-specific defences red blood cells trapped in a network of fibrin threads platelet plug Protects the body from invasion by pathogens Stops further bleeding 20.4 Specific defences 20.4 Specific defences If a pathogen is able to get past the body’s non-specific defences the immune system will start off a series of specific defences that attack the pathogens These are called immune responses 20.4 Specific defences white blood cells Phagocytes Lymphocytes Perform phagocytosis to kill pathogens Produce antibodies to kill pathogens Non-specific response Specific response 20.4 Specific defences antigen stimulates Lymphocytes bacterium to produce antibodies 20.4 Specific defences Antibodies 1 They are produced by lymphocytes 2 3 Their functions is to remove antigens Their actions are specific i.e. a kind of antibodies only attacks its corresponding antigen 20.4 Specific defences How do antibodies work? 1. Attach the surface of the antigen bacterium 3. The pathogen bursts antigen bacterium bacterium antibody 2. Make holes on the wall of the pathogens 20.4 Specific defences How do antibodies work? antibody bacterium 1. Attach to the surface of the pathogen 2. Phagocyte can engulf the bacterium more easily 3. The pathogen is killed by the phagocyte 20.4 Specific defences How do antibodies work? Cause the pathogens to clump together Lower their harmful activities antibody antigen on pathogen 20.4 Specific defences How do antibodies work? Combines directly with toxins secreted by bacteria make them harmless antitoxin toxin antibody 20.4 Specific defences Primary Secondar y Antibody concentration 20.4 Specific defences 1st exposure to antigen X Time (days) 20.4 Specific defences Antibody concentration There is no antibody production until day 7 1st because the rate of production of antibodies is very slow This period is called latent period * * exposure to antigen X Time (days) 20.4 Specific defences Antibody concentration After day 17, the rate of production of antibodies is decreasing 1st because the amount of antigens is decreasing exposure to antigen X Time (days) 20.4 Specific defences Antibody concentration When the body is exposed to the same antigen again 1st 3 The amount of antibodies is very large 1 Latent period is very short exposure to antigen X 2nd 2 The rate of production of antibodies is very fast exposure to antigen X Time (days) 20.4 Specific defences Antibody concentration Primary response 1st Secondary response Why the secondary response is different from the primary one ? exposure to antigen X 2nd exposure to antigen X Time (days) 20.4 Specific defences After the primary response Some white blood cells memorise the antigen 1 When the body is exposed to the same antigen again a much larger amount of phagocytes and antibodies is produced 2 in a shorter time This response is called secondary response 20.5 Immunity and vaccination 20.5 Immunity and vaccination Immunity If the same antigen re-enters the body again the body can produce a large amount of antibodies quickly antibody level becomes high enough to give protection against pathogen The readiness of the body to resist disease in this way is called immunity 20.5 Immunity and vaccination Acquired Immunity If a person’s immunity is acquired by actual contact with the antigen It is known as acquired immunity 20.5 Immunity and vaccination Acquired Immunity Natural immunity achieved by infection Artificial immunity achieved by vaccination or injection of a serum 20.5 Immunity and vaccination Vaccination We can be immunised against a disease by receiving a vaccine This process is called vaccination Dead or weakened pathogen s 20.5 Immunity and vaccination Primary response After vaccine is injected some white blood cells memorise the antigen Subsequent exposure to the same type of antigen the white blood cells will take the response to produce a large amount of specific antibodies quickly Secondary response 20.5 Immunity and vaccination Vaccination programme is set up by the Health Department in HK Measles Rubella Viral Poliomyelitis hepatitis B Tetanus Mumps Diphtheria Whooping cough 20.5 Immunity and vaccination Injection of serum contains antibodies antibody level After injection of serum, injection of serum antibodies will be immediately available to limit the development of disease 20.5 Immunity and vaccination Injection of serum contains antibodies antibody level High antibody level does not last long injection of serum because the antibodies will be broken down and rejected 20.5 Immunity and vaccination Serum injection Vaccination immediate immunity slower immunity short-lived long-lived Mind Map Body defence readiness of body to resist disease can be divided into against non-specific defences diseases specific defences include include 1. infectious diseases 2. non-infectious diseases are 1. physical barrier immune responses 2. chemical barrier include 3. phagocytes involve the production of antibodies 4. blood clotting by lymphocytes secondary immune responses primary immune responses immunity can be achieved artificially by 1. vaccination 2. injection of serum