Anatomy & Physiology

Anatomy & Physiology Study Guide destroy it by releasing toxic chemicals, such as tumor necrosis factor, nitric oxide, or hydrogen peroxide, into the interstitial fluid. Immunological Surveillance The constant monitoring of normal tissues by NK cells is called immunological surveillance. NK cells are much less selective about their targets than are other lymphocytes: They respond to a variety of abnormal antigens that may appear anywhere on a plasma membrane, and anymembrane containing abnormal antigens will be attacked. NK cells also respond much more rapidly than T cells or B cells. Interferons Interferons are small proteins released by activated lymphocytes and macrophages and by tissue cells infected with viruses. On reaching the membrane of a normal cell, an interferon binds to surface receptors on the cell and triggers the production of antiviral proteins in the cytoplasm. Antiviral proteins do not interfere with the entry of viruses, but they do interfere with viral replication inside the cell. Interferons stimulate the activities of NK cells and macrophages and slow the spread of viral infection. At least three types of interferons exist, each of which has additional specialized functions: Alpha- (α) interferons, produced by several types of leukocytes, attract and stimulate NK cells; beta- (β) interferons, secreted by fibrocytes slow inflammation in a damaged area; and gamma-(γ) interferons, secreted by T cells and NK cells, stimulate macrophage activity. Interferons are examples of cytokines—chemical messengers released by tissue cells to coordinate local activities. Complem nt Plasma contains 11 special complement (C) proteins that form the complement system. The term complement refers to the fact that this system complements the action of antibodies. The complement proteins interact with one another in chain reactions, or cascades, reminiscent of those of the clotting system. The activation of complement can occur by two different routes: the classical pathway and the alternative pathway. Known effects of complement activation include the stimulation of inflation, the attraction of phagocytes, the enhancement of phagocytes, and the destruction of target plasma membrane. Inflammation Inflammation, or the inflammatory response, is a localized tissue response to injury. Inflammation produces local swelling (tumor), redness (rubor), heat (calor), and pain (dolor); these are known as the cardinal signs and symptoms of inflammation. Inflammation has several effects. The injury is temporarily repaired, and additional pathogens are prevented from entering the wound. The spread of pathogens away from the injury is slowed. Local, regional, and systemic defenses are mobilized to overcome the pathogens and facilitate permanent repairs. This repair process is called regeneration. Fever Fever is the maintenance of body temperature greater than 37.2°C (99°F); although, a fever is not clinically significant until greater than 38°C. Circulating proteins, called pyrogens, can reset this thermostat and raise the body temperature. A variety of stimuli, including pathogens, bacterial toxins, and antigen–antibody complexes, either act as pyrogens themselves or stimulate the release of pyrogens by macrophages. Achieve Page 285 of 368 ©2018