Chapter 47 part 1

• Phagocytosis


  1. Phagocytic cell extends pseudopod to surround pathogen

  2. Pathogen engulfed by phagocytic cell through endocytosis

  3. Vacuole forms around pathogen

  4. Lysosomes fuse with vacuole and digest pathogen

  5. Debris released from phagocytic cell through exocytosis
• Phagocytosis


  • Type of innate immune response
  • First line of defense against infection
  • Present in all animals
  • Involves physical barriers and phagocytic cells
  • Phagocytic cells recognize and engulf pathogens
  • Engulfed pathogens are destroyed by enzymes
• Antiviral defense in insects

  1. Viral RNA enters insect cell

  2. Viral RNA replicates forming double-stranded RNA

  3. Dicer-2 enzyme recognizes double-stranded RNA and cuts it into fragments

  4. Argo protein complex binds to RNA fragment and displaces one strand

  5. Argo complex uses bound strand to identify and cut viral mRNA, stopping viral protein production
• Toll-like receptors (TLRs)


  • Proteins on immune cell surfaces
  • Recognize pathogen-associated molecular patterns (PAMPs)
  • Each TLR recognizes a specific PAMP
  • TLR binding to PAMP triggers signaling cascade
  • Signaling leads to production of inflammatory molecules like cytokines
  • Cytokines activate other immune cells and promote adaptive immune response
  • TLRs on cell membrane detect extracellular pathogens
  • TLRs in vesicles detect intracellular pathogens
• Lymphatic system


  • Network of vessels transporting lymph fluid
  • Lymph contains waste, excess fluids, and immune cells
  • Lymph nodes filter lymph and contain immune cells
  • Lymph vessels collect fluid from tissues and drain into ducts near shoulder
  • Interstitial fluid forms lymph
  • Plays role in immunity by filtering lymph and transporting immune cells
  • Includes appendix and Peyer's patches as lymphoid organs
  • Involved in inflammatory response by transporting lymph to infection site