Immune System Study Guide Defense Mechanisms First Line External Barriers Skin Mechanical protection Chemical protection keratinized cells of epidermis protect against penetrating pathogens or microbial growth Microbials that do adhere to epidermis are shed off with dead skin Sebum from sebaceous glands Acid mantle pH 3 5 is a thin film of lactic acid that inhibits bacterial growth also contains defensins which destroy bacteria viruses and fungi Line the body cavities that are open to the outside to trap microbes and foreign substances lines respiratory digestive urinary and reproductive Mucus tears and saliva contain lysozyme an enzyme that destroys bacteria by dissolving their cell walls Mucous Membranes Second Line Phagocytic cells both 2nd and 3rd lines of defense Neutrophils kill bacteria either through phagocytosis or respiratory burst a reaction occurs that produces a bactericidal chemical kills bacteria but also kills neutrophil can be harmful to body Eosinophils kills parasites and allergens produces toxic proteins secrete anti histamine vasoconstrictor Basophils secretes histamine vasodilator and heparin inhibits blood clots to allow for better leukocyte mobility Lymphocytes Monocytes Natural Killer NK cells leukocytes that emigrate from blood and transform into macrophages in tissue Antimicrobial proteins provide short term resistance against bacteria and virus Interferons proteins secreted when certain cells are infected with viruses prevents multiplication of virus activate natural killer cells and macrophages may promote cancer cell destruction Complement System a group of 30 or more globulins that make contributions to both nonspecific and specific immunity completes the action of antibody produced by liver always present in blood plasma are activated by the presence of pathogens 3 pathways Classical requires an antibody to get started specific immunity Alternative no antibody required nonspecific Lectin no antibody required nonspecific End Results of Complement System Immune surveillance Inflammation Fever Third Line Specific Immunity