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The Immune System Infectious Disease • Pathogens are disease-causing “invaders” • Infectious diseases can be spread by contact with infected people, animals, water, or food. • Four ways to transmit infectious diseases (with examples): Direct contact: shaking hands or sharing drinks or bodily fluids with an infected person Indirect contact: being near an infected person who sneezes without covering his or her mouth Water and food: eating foods infected with certain bacteria, ex, Salmonella. Drinking water infected with E.coli bacteria can also result in serious illness. Animal bites: being bitten by an animal carrying rabies Immune System: First Line of Defence • The skin and the linings of all internal body systems. Sweat and oil are acidic. • Gastric juice is acidic, and can destroy pathogens. Second Line of Defence: Innate Immune Response • Quick and general • Usually fight bacteria and some viruses. • First action is a flow of fluid, cells, and dissolved substances to the infection site. • Fever, inflammation and redness occurs. • A type of white blood cells called phagocytes will increase in number. • The phagocytes engulf and swallow the pathogens. Acquired Immune Response • Highly specific attack on a pathogen, or antigen. • An antigen is any substance the body cannot recognize, it is a non-living particle or substance • Your body uses WBC’s called B cells and T cells to respond. • The process can take up to a week. • B cells recognize antigens and produce specific particles, called antibodies to fight them. • Antibodies attach and destroy antigens and pathogens carrying antigens. • T cells: helper T cells recognizes an antigen or pathogen and activates B cells. • T cells: killer T cells work independently and destroy antigens or pathogens. • All acquired immune responses help give you active immunity. Your body remembers which antibodies should be used to attack a pathogen that it has seen before. • Memory B cells store the new antibodies Factors Affecting the Immune System Vaccinations • Vaccines: a special version of an antigen that gives you immunity against a disease. • Vaccines are like weakened forms of a disease, they stimulate your immune system to create antibodies against the disease. • These antibodies are reactivated to fight the antigen if it enters your body. • Some vaccines require booster shots. • All grade 9 students receive booster shots for tetanus, diptheria, and pertussis. Disorders of the Immune System • Allergies: an unusually high sensitivity to some substance. • Something that causes an allergic reaction is an allergen. • The allergen acts as an antigen for you, and your immune system kicks in. • The symptoms of an allergy are cause by a substance called histamine, that your body releases. • A severe reaction to an allergen is called anaphylactic shock, and can result in breathing difficulty, swelling, and sometimes death. Acquired Immunodeficiency Syndrome (AIDS) • AIDS is an infection of the immune system. • AIDS is caused by the human immunodeficiency virus (HIV). • HIV attacks the immune system itself, and destroys it by infecting helper T cells. • The immune system becomes unable to defend against pathogens or antigens. • A person infected with HIV can die from other, less serious infections. • AIDS has resulted in the death of more than 11 million people, and currently affects more than 40 million people. • HIV is transmitted in two body fluids, semen and blood. • People are infected by unsafe behaviour, such as having sex with a person who has HIV without using a condom, or sharing contaminated needles. • HIV cannot be transmitted by casual contact such as shaking hands.