Week 6 Physiology

WBC functions (broad concepts)

Innate immune system – does not require previous sensitisation to attack a foreign protein

  • Macrophages
  • Neutrophils
  • Barriers
  • Eosinophils
  • Basophils
  • Natural Killer cells
  • Complement system


Humoural immunity

  • B lymphocytes – bind to antigen on MHC II molecules, each B cell has a different antigen receptor(Ab), once bound it becomes activated and increase in number and can specialise into plsama cells which secrete Abs
  • Ab opsonise, activate complement and start inflammation or inactivate the target without causing cell damage or inflammation
  • T helper cells assist
  • Aimed at extracellular antigens


Cellullar immunity

  • T lymphocytes
  • CD8 cells identify antigens in MHCI molecules and become activated and kill the cell if foreign/tumour material is identified in  MHC I
  • Activation is assisted by T helper cells
  • Aimed at intracellular pathogens and tumours



  • Cascade of proteins from 1 -9
  • MAC complex – C5b-C9 puts holes in antigen membranes
  • C5a – chemotaxis, leukocyte adhesion, activation, migration,  and inflammation via increased vasc permeability(histamine release)
  • C3b – opsonises
  • C3a – anaphylotoxin – trigger degranulation of endothelial cells, mast cells or phagocytes – if localised it is inflammation, if generalised it can be similar to anaphylaxis


  • Classical pathway
    • Activated by Ag – Ab complex
  • Alternative pathway
    • stim by microbial surface molecules
  • Lecithin pathway
    • stim by plasma mannose binding lectin binds to carb on bacterial
  • All pathways cleave and activate C3 – most abundant one.


Cytokines (broad concepts)

  • Attracts immune cells – gradient generated leads to chemotaxis
  • Assists in activation of immune cells eg IL4, IL1, TNF a
  • Contributes to immune response eg fever


Viva questions:

  • How is the Immune System organised ; i.e. what are it’s major components ?

    Ganong's Review of Medical Physiology, 24th Edition

    Ganong’s Review of Medical Physiology, 24th Edition

  • What is the body’s response to an antigen ?
  • What is the MHC ? What is it’s role ?
  • Draw an immunoglobulin molecule.
    • Long chain
    • Short chain
    • F constant(Fc) at bottom and F variable(Fab) at top(to bind different antigens)
  • Describe the complement system.
  • What are anaphylatoxins and what is their role ?
  • Tell me about the classical/alternative pathway.
  • What are cytokines and what do they do ?