HYPERSENSITIVIT1 - leukotrienes and prostaglandins. The...

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HYPERSENSITIVITY (ALLERGY)   Allergies are a reaction to an antigen which is called an allergen. Allergens themselves are not  harmful and do not provoke a reaction in everyone. Some individuals become sensitized to a  particular allergen, which the immune systems of most of the population  ignore. The resulting  reaction causes tissue damage which can be anywhere from mildly annoying to miserable to fatal.    1. Type I (anaphylactic) reactions—these can be the most severe and dangerous allergic  reactions.  They occur when IgE antibodies are formed against a particular allergen. These  antibodies attach to mast cells and basophils. When the allergen enters the body and comes in  contact with these antibodies, the chemical mediator histamine is rapidly released from granules  inside the basophils and mast cells. These cells also produce and release other mediators such as 
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Unformatted text preview: leukotrienes and prostaglandins. The chemical mediators cause increased permeability of capillaries, increased secretion of mucus, smooth muscle contraction, etc. a. Systemic anaphylaxisvery large amounts of the chemical mediators are released and cause circulatory collapse and constriction of air passages which may lead to death. Epinephrine can counteract this. b. Local anaphylaxisless severe, less release of mediators. Usually associated with ingested or inhaled antigens. Effects include hives, asthma, hay fever, gastrointestinal upsets, etc. Repeated injections of tiny amounts of the allergen may succeed in desensitization. IgG antibodies are formed, which block the antigen by binding to it before it can reach the IgEs....
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