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Unformatted text preview: Chapter 43 The Immune System Reconnaissance, Recognition, and Response • An animal must defend itself from microorganisms – it may encounter many dangerous pathogens in the environment Two major kinds of defenses have evolved that counter these threats: • Innate immunity – Is present before any exposure to pathogens and is effective from the time of birth – Involves nonspecific responses to pathogens • Acquired immunity, also called adaptive immunity – Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances – Involves a very specific response to pathogens Innate immunity provides broad defenses against infection • A pathogen that successfully breaks through an animal’s external defenses soon encounters several innate cellular and chemical mechanisms that impede its attack on the body • Intact skin and mucous membranes – Form physical barriers that bar the entry of microorganisms and viruses • Certain cells of the mucous membranes produce mucus – A viscous fluid that traps microbes and other particles • In the trachea, ciliated epithelial cells – Sweep mucus and any entrapped microbes upward, preventing the microbes from entering the lungs • Secretions of the skin and mucous membranes – Provide an environment that is often hostile to microbes • Secretions from the skin – Give the skin a pH between 3 and 5, which is acidic enough to prevent colonization of many microbes – Also include proteins such as lysozyme , an enzyme that digests the cell walls of many bacteria Internal Cellular and Chemical Defenses • Depend mainly on phagocytosis by phagocytes o types of white blood cells o Ingest invading microorganisms o Initiate the inflammatory response Phagocytic Cells • Phagocytes attach to their prey via surface receptors and engulf them, forming a vacuole that fuses with a lysosome • Macrophages , a specific type of phagocyte – Can be found migrating through the body – Can be found in various organs of the lymphatic system – The lymphatic system plays an active role in defending the body from pathogens • About 30 proteins make up the complement system – causes lysis of invading cells and helps trigger inflammation • Interferons – Provide innate defense against viruses and help activate macrophages Inflammatory Response • In local inflammation, histamine and other chemicals released from injured cells – Histamine promotes changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues • Natural Killer Cells – Patrol the body and attack virus-infected body cells and cancer cells – Trigger apoptosis in the cells they attack Invertebrate Immune Mechanisms • Many invertebrates defend themselves from infection – By many of the same mechanisms in the vertebrate innate response Lymphocytes provide specific defenses against infection • Acquired immunity – Is the body’s second major kind of defense...
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- Spring '08