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Discover the essential components of innate immunity, the frontline defense against infections. Learn about external barriers like skin and mucous membranes, as well as internal defenses involving phagocytosis by white blood cells. Explore the lymphatic system's role in fighting pathogens and how antimicrobial proteins, interferons, and the inflammatory response contribute to immunity. Dive into the mechanisms of Natural Killer (NK) cells and their vital role in identifying and eliminating virus-infected and cancer cells.
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Chapter 43 The Immune System
Concept 43.1: Innate immunity provides broad defenses against infection • A pathogen that breaks through external defenses encounters innate cellular and chemical mechanisms that impede its attack
External Defenses • Skin and mucous membranes are physical barriers to entry of microorganisms and viruses • Secretions of the skin and mucous membranes provide an environment hostile to microbes
External Defenses • Secretions give the skin a pH between 3 and 5, acidic enough to prevent colonization of many microbes • Skin secretions include proteins such as lysozyme, which digests bacterial cell walls
External Defenses • Mucous membrane cells 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 microbes from entering the lungs
Internal Cellular and Chemical Defenses • Internal cellular defenses depend mainly on phagocytosis • White blood cells called phagocytesingest microorganisms and initiate inflammation
Phagocytic Cells Microbes Pseudopodia • Phagocytes attach to prey via surface receptors and engulf them, forming a vacuole that fuses with a lysosome MACROPHAGE Vacuole Lysosome containing enzymes
Macrophages, a type of phagocyte, migrate through the body and are found in organs of the lymphatic system • The lymphaticsystemdefends against pathogens
Lymphatic capillary Interstitial fluid Adenoid Tonsil Blood capillary Lymph nodes Lymphatic vessel Spleen Tissue cells Peyer’s patches (small intestine) Appendix Lymphatic vessels Masses of lymphocytes and macrophages Lymph node
The Lymphatic System • Drains excess fluid • Into veins near the heart • Temporary reservoir for fluids • Carry hormones throughout the body • Carries fat molecules to the regular vessels • Part of the immune system
Antimicrobial Proteins • Proteins function in innate defense by attacking microbes directly or impeding their reproduction • About 30 proteins make up the complement system, which 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 promote changes in blood vessels • These changes allow more fluid, phagocytes, and antimicrobial proteins to enter tissues Pin Blood clot Pathogen Macrophage Blood clotting elements Chemical signals Phagocytic cells Phagocytosis Capillary Red blood cell
Natural Killer Cells“better safe than sorry” • Natural killer (NK) cells attack virus-infected body cells and cancer cells • Recognizes cells that contain “non-self” proteins • They trigger apoptosis in the cells they attack
