Defense against infectious disease

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Defense against infectious disease
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Pathogens

• Disease-causing agents
• Viruses
• Bacteria
• Protists
• Fungi
• Worms

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Defense against pathogensAntibiotics

• Only work against bacteria
• Take advantage of differences between bacterial
  cells and our cells (selective toxicity)
• Block protein synthesis in bacteria -
  erythromycin
• Inhibit production of cell walls - penicillin
• No effect on viruses no metabolism
• Would harm our cells since viruses use them
• Overuse leads to resistance, can become a problem
  throughout the world

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Nonspecific Resistance Innate Defenses

• Present at birth
• Offers immediate protection against a wide
  variety of pathogens
• Functions in the same way against any invader

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Nonspecific Resistance Innate Defenses

• skin, mucous membranes, and secretions
• Mechanical protection
• Epidermis top layer of skin (dead cells
  constantly being replaced)
• mucous membranes of trachea, nose, urethra, and
  vagina
• lacrimal apparatus, saliva, flow of urine,
  vaginal secretions, defecation and vomiting
• Chemical protection
• Gastric juice is acidic
• Lysozyme is an enzyme component of tears,
  perspiration, and nasal secretions that can break
  down the cell walls of certain bacteria

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Blood clotting

• Seals damaged vessels to prevent blood loss and
  prevent pathogens from entering body
• A clot is a gel consisting of a network of
  insoluble protein fibers (fibrin) in which formed
  elements of blood are trapped
• Stimulated by chemicals released by damaged
  cells, platelets, and plasma

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Events of clotting

• Clotting proteins, prothrombin and fibrinogen,
  are always present in blood plasma but remain
  inactive
• Clotting factors convert prothrombin to thrombin
• Thrombin is an enzyme that catalyses the
  conversion of soluble fibrinogen into insoluble
  fibrin

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Platelet Aggregation

• Activated platelets stick together and activate
  new platelets to form a mass called a platelet
  plug
• Plug reinforced by fibrin threads formed during
  clotting process

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• What happens when pathogens do gain access to
  blood stream?

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Nonspecific Resistance Innate Defenses

• Internal defenses
• Phagocytes perform phagocytosis
• Large white blood cells produced in bone marrow
• Wandering macrophages circulate in blood stream
  or can leave blood vessels due to amoeboid
  movement and change in shape
• Fixed macrophages histiocytes (connective
  tissue), Kupffer cells (liver), microglia
  (nervous system)
• Nonspecific because identity of pathogen is not
  determined treats all nonself the same

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Steps of PhagocytosisFig. 43.4 p. 900

• Recognition based on protein molecules on
  surface of cell or virus (identify as self or
  nonself)
• Ingestion pseudopods engulf microbe through
  amoeboid motion and endocytosis
• Vacuole formation vacuole contains microbe
• Digestion vacuole merges with lysosome and
  enzymes destroy microbes
• Exocytosis microbial debris is released from
  cell