AP Immune System Essay

* AP IMMUNE SYSTEM * An animal must defend itself against unwelcome intruders -- the many potentially dangerous viruses, bacteria, and other pathogens it encounters in the air, in food, and in water. * Herpes simplex-1 (Herpes labialis, HSV-1) * Herpes simplex 2 (HSV-2, Herpes genitalis) on thigh * Three cooperative lines of defense have evolved to counter these threats. * Two of these are nonspecific -- that is, they do not distinguish one infectious agent from another. * The first line of nonspecific defense is external, consisting of epithelial cells that cover and line our bodies and the secretions they produce. * The second line of nonspecific defense is internal, involving phagocytic cells and antimicrobial
* Some macrophages migrate throughout the body, while others reside permanently in certain tissues, including the lung, liver, kidney, connective tissue, brain, and especially in lymph nodes and the spleen. * The fixed macrophages in the spleen, lymph nodes, and other lymphatic tissues are particularly well located to contact infectious agents. * Interstitial fluid, perhaps containing pathogens, is taken up by lymphatic capillaries, and flows as lymph, eventually returning to the blood circulatory system. * Along the way, lymph must pass through numerous lymph nodes, where any pathogens present encounter macrophages and lymphocytes. * Microorganisms, microbial fragments, and foreign molecules that enter the blood encounter macrophages when they become trapped in the netlike architecture of the spleen. * Eosinophils, about 1.5% of all leukocytes, contribute to defense against large parasitic invaders, such as the blood fluke, Schistosoma mansoni. * Eosinophils position themselves against the external wall of a parasite and discharge destructive enzymes from cytoplasmic