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Campbell-Reece Biology - 6th Edition - Presentation Notes

Campbell-Reece Biology - 6th Edition - Presentation Notes ...

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Chapter 43 The Immune System Lecture Outline Overview: Reconnaissance, Recognition, and Response 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. It must also deal with abnormal body cells, which, in some cases, may develop into cancer. Two major kinds of defense have evolved to counter these threats. The first kind of defense is innate immunity. ° Innate defenses are largely nonspecific, responding to a broad range of microbes. ° Innate immunity consists of external barriers formed by the skin and mucous membranes, plus a set of internal cellular and chemical defenses that defend against microbes that breach the external barriers. ° The internal defenses include macrophages and other phagocytic cells that ingest and destroy pathogens. A second kind of defense is acquired immunity. ° Acquired immunity develops only after exposure to microbes, abnormal body cells, or other foreign substances. ° Acquired defenses are highly specific and can distinguish one inducing agent from another. ° This recognition is achieved by white blood cells called lymphocytes, which produce two general types of immune responses. In the humoral response, cells derived from B-lymphocytes secrete defensive proteins called antibodies that bind to microbes and target them for elimination. In the cell-mediated response, cytotoxic lymphocytes directly destroy infected body cells, cancer cells, or foreign tissue. Concept 43.1 Innate immunity provides broad defenses against infection An invading microbe must penetrate the external barrier formed by the skin and mucous membranes, which cover the surface and line the openings of an animal’s body. Lecture Outline 43-1
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If it succeeds, the pathogen encounters the second line of nonspecific defense, innate cellular and chemical mechanisms that defend against the attacking foreign cell. The skin and mucous membrane provide first-line barriers to infection. Intact skin is a barrier that cannot normally be penetrated by bacteria or viruses, although even minute abrasions may allow their passage. Likewise, the mucous membranes that line the digestive, respiratory, and genitourinary tracts bar the entry of potentially harmful microbes. ° Cells of these mucous membranes produce mucus, a viscous fluid that traps microbes and other particles. ° In the trachea, ciliated epithelial cells sweep out mucus with its trapped microbes, preventing them from entering the lungs. Beyond their role as a physical barrier, the skin and mucous membranes counter pathogens with chemical defenses. ° In humans,
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Campbell-Reece Biology - 6th Edition - Presentation Notes ...

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