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Microbiology: Human Body Defense Mechanisms

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  • What are the three lines of defense in the human body?

    The first line is physical and chemical barriers; the second line is innate immune responses like phagocytosis and inflammation; the third line is adaptive immunity involving specific responses by lymphocytes.

  • What is species resistance?

    Species resistance is the natural immunity a species has against certain pathogens that do not infect it due to physiological differences.

  • How does innate immunity differ from species resistance?

    Innate immunity is the nonspecific defense present at birth protecting against all pathogens, while species resistance is immunity due to species-specific traits.

  • What characteristics of the skin prevent pathogen entry?

    The skin acts as a physical barrier with tightly packed cells, a dry surface, and acidic pH, plus antimicrobial secretions that inhibit pathogen growth.

  • How do mucous membranes protect the body?

    Mucous membranes trap pathogens with mucus, contain antimicrobial enzymes, and have cilia that move trapped microbes out of the respiratory tract.

  • What is the lacrimal apparatus and its role in infection control?

    The lacrimal apparatus produces tears that wash away microbes and contain lysozyme, an enzyme that destroys bacterial cell walls.

  • How does the microbiome protect against disease?

    The microbiome competes with pathogens for nutrients and space, produces antimicrobial substances, and stimulates the immune system.

  • What are antimicrobial peptides and their role in defense?

    Antimicrobial peptides are small proteins that disrupt microbial membranes, providing a rapid defense against bacteria, fungi, and viruses.

  • Contrast the first and second lines of defense against disease.

    The first line includes physical and chemical barriers preventing entry; the second line involves internal cellular defenses like phagocytes, inflammation, and fever.

  • What are the main components of blood involved in defense?

    Blood contains white blood cells (leukocytes) like neutrophils and macrophages for defense, platelets for clotting, and plasma with antibodies and complement proteins.

  • What are the six stages of phagocytosis?

    1. Chemotaxis, 2. Adherence, 3. Ingestion, 4. Formation of phagosome, 5. Fusion with lysosome, 6. Digestion and exocytosis of debris.

  • How do Toll-like receptors (TLRs) relate to pathogen-associated molecular patterns (PAMPs)?

    TLRs on immune cells recognize PAMPs, molecular structures unique to pathogens, triggering immune responses.

  • Compare the roles of interferons and the complement system in innate immunity.

    Interferons inhibit viral replication and activate immune cells; the complement system enhances phagocytosis, inflammation, and lyses pathogens.

  • What is the process and benefit of inflammation?

    Inflammation involves vasodilation, increased permeability, and leukocyte migration to isolate and destroy pathogens and promote tissue repair.

  • What role does fever play in fighting infection?

    Fever raises body temperature to inhibit pathogen growth and enhances immune cell activity.

  • How are biochemical test media used in bacterial identification?

    Biochemical media test for bacterial enzyme activities and metabolic traits, helping differentiate species based on their biochemical reactions.

  • What is the purpose of differential test systems in bacterial identification?

    Differential tests distinguish bacteria by observable changes like color shifts or gas production in specific media.