CHAPTER 43 THE BODY’S DEFENSES

Nonspecific mechanisms and general barriers Skin-water proof and impenetrable if unbroken; acidity of sweat and normal bacteria flora inhibit pathogens Lysozymes in perspiration, tears and saliva attacks cell walls of many bacteria Stomach acid kill most bacteria in food

Hair and cilia in respiratory tracts traps bacteria and viruses

Neutrophils-most numerous, attracted by chemical signals, become amoeboid, phagocytic, living only a few days Monocytes-macrophages-larger, longer lived, wander through interstitial fluid, found in connective tissue, lymph nodes, and spleen, interact with T-cells

Eosinophils-enzymes against parasitic worms Natural killer cells-lyse infected or abnormal cells, similar to cytotoxic T’s but less discriminatory Basophils (circulating)-and mast cells (in connective tissue) degranulate releasing histamines that cause vasodilation of local capillaries and makes them leakier Dendritic cells-are a type of blood cell that have the ability to stimulate an immune response against specific targets and are being widely pursued as a new treatment for cancer and viral diseases. Phagocytic, and interact with T & B cells

Cytotoxic T cells killing a cancerous cell

Inflammatory Response Injured tissue releases prostaglandins and histamines that causes basophils and mast cells to release more histamines causing: –Vasodilation of capillaries and increased blood flow –Capillaries to become leakier –Increased metabolic rate and local temperature rises –Neutrophils become amoeboid and leave capillaries and begin to phagocytize –Monocytes become macrophages and move into the area and begin phagocytizing then become antigen presenting cells and release interleukin 1 to attract T cells -- Dendritic cells phagocytize and present antigens to T & B cells

Inflammatory Response Toxins and pyrogens cause fever Various chemicals released cause pluripotent stem cells to divide more rapidly Natural killers in area check locals cell’s MHC I’ s for antigens Viral infected cells release interferon Complements stick to pathogens and lyse or induce opsonization T lymphocytes and B lymphocytes are alerted and move into the area

Phagocytosis by a macrophage

Clonal Selection-the antibodies of each B cell only recognize certain antibodies but collectively they should recognize any antigen

B lymphocyte

T cell infected with HIV

Close-up of T cell infected with HIV

Arthritis

Rh factor When an Rh + fetus is carried by an Rh - mother, during birth or the last few days before birth, some Rh + blood can go into the mother’s body and she will make antibodies against it. That child will not have a problem because it is born before the antibodies are produced. However any subsequent Rh + fetus will get antibodies form the mother that will attack its blood resulting in hemolytic anemia and death. To prevent this problem, Rh - mothers are given an injection of Rhogan that contains small amounts of Rh + antibodies two or three times during their pregnancies.