micropara

• Non Specific Host Defense Mechanism


  The body's first line of defense against pathogens, not involving the immune system
• First line of defense

  • Skin
  • Mucous membrane
• Skin's ability to resist pathogens

  • Dryness inhibits colonization
  • Acidity and temperature inhibit growth
  • Oil sebum is toxic to some pathogens
  • Perspiration contains lysozyme that destroys bacterial cell walls
  • Soughing dead skin removes pathogens
• Mucous


  • Contains lysozyme that destroys peptidoglycan
  • Contains lactoferrin that binds iron needed by pathogens
  • Contains lactoperoxidase that produces toxic superoxide radicals
• Digestive tract defenses


  • Digestive enzymes
  • Acidity of stomach
  • Alkalinity of intestine
  • Bacteria trapped in mucous lining and destroyed by enzymes
• Urinary tract defenses


  • Frequent urination flushes microorganisms from urethra
• Respiratory system defenses


  • Cilia
  • Lysozyme in saliva
• Humans swallow approximately 1 liter of saliva per day
• Microbial antagonism


  • Normal flora prevent colonization by other organisms
  • Inhibitory capability of indigenous microflora
  • Competition for colonization sites
  • Competition for nutrients
  • Production of substances that kill other bacteria
• Inflammation


  • Response to local injury, irritation, microbial invasion or bacterial toxin
  • Cardinal signs: redness, heat, swelling, pain
• Acute inflammation


  1. Increase diameter of capillaries

  2. Increase permeability of capillaries, allowing escape of plasma and proteins

  3. Exit of WBC from capillaries and accumulation at site of injury
• Sequence of inflammatory response

  1. Tissue injury

  2. Vasodilatation

  3. Increase permeability

  4. Emigration of WBC

  5. Chemotaxis

  6. Phagocytosis
• Purposes of inflammatory response

  • Localize an infection
  • Prevent spread of microbial invaders
  • Neutralize any toxins
  • Repair damaged tissue
• Inflammatory exudates


  Accumulation of fluid, cells, and cellular debris at the inflammation site
• Pyocyanin


  Bluish green pigment
• Pus


  Yellow, thick, greenish fluid containing live and dead WBC
• Phagocytes


  Phagocytic white blood cells
• Phagocytosis


  Process by which phagocytes surround and ingest foreign materials
• Professional phagocytes


  • Macrophages
  • Neutrophils
• Macrophages


  • Wandering macrophages leave blood vessels and migrate to infected area
  • Fixed macrophages (histiocytes) remain in tissues and organs to trap foreign debris
• Reticuloendothelial system


  System containing macrophages found in liver, spleen, lymph nodes, bone marrow, lungs, blood vessels, intestine, and brain
• Chemotaxis


  Attraction of phagocytes to the site where they are needed
• Steps in phagocytosis


  1. Chemotaxis

  2. Attachment

  3. Ingestion

  4. Digestion
• Chemokines


  Chemotactic agents produced by various cells of the human body
• Second line of defense

  • Transferrin
  • Pyrogens
  • Interferons
  • Complement system
  • Acute phase proteins
  • Cytokines
• Transferrin


  Serves as defense by depriving pathogens of essential iron
• Pyrogens


  Stimulate the production of fever, which augments host defenses
• Interferons


  • Alpha (produced by B lymphocytes, monocytes, macrophages)
  • Beta (produced by fibroblasts and other virus-infected cells)
  • Gamma (produced by activated T lymphocytes, natural killer cells)
• Complement system


  Group of proteins that complement the action of the immune system
• Complement system results


  • Initiation and amplification of inflammation
  • Attraction of phagocytes (chemotaxis)
  • Activation of leukocytes
  • Lysis of bacteria and other foreign cells
• Acute phase proteins


  Increase rapid response to infection, inflammation and tissue injury
• Cytokines


  Chemical messengers between the immune system and other systems of the body