Chapter 48

The Immune system

The functions of the immune system

• Provides defense against pathogens
  • Pathogens are disease causing organisms
  • Prokaryotes and eukaryotes
• Defense against cancer by recognizing and eliminating grossly abnormal cells: immune surveilance

Cells of the immune system

• Leukoctyes - general term for the cells of the immune system
  
  • White blood cells
  • Derived from a common precursor in the bone marrow
  • Circulate in the blood and lymphatic fluids to tissues all around the body
• Granulocytes
  • Contain visible granules in their cytoplasm
  • Secrete chemicals that attack pathogens or that change the behavior of host tissues near a site of infection
  • Includes basophils, mast cells
  • Also includes eosinophils and neutrophils, which are also phagocytic
• Phagocytes
  • Phagocytose foreign marterial or debris from dead infected cells
  • Includes macrophages, monocytes, basophils, and dendritic cells
  • Neutrophils and eosinophils are also phagocytic, but technically eosinophils
    • Technically granulocytes if you categorize based on appearance, but highly phagocytotic
• Lymphocytes
  • Recognize specific pathogens or cells that have been infected by a pathogen
  • Includes B cells, T cells, and NK cells

The immune system

Innate immunity

• First line of defense
  • Anatomical barriers (e.g. epithelial coverings)
  • Physiological barriers (e.g. secretions)
  • Promotion of non-pathogenic microbes
• Second line of defense
  • Granulocytes, phagocytes, and NK cells
  • Inflammatory response
  • Complement system
    • A series of proteins secreted the liver that circulate in the blood and lymphatic fluid and get activated by the signals that lymphocytes secrete near sites of infection
• Not specific to the type of infection

Adaptive (acquired) immunity

• Third line of defense
  • More targeted, more specific
  • B cells produce and secrete antibodies that target extracellular pathogens
  • Cytotoxic T cells target and kill infected cells to limit the ability of pathogens to reproduce
  • Helper T cells are necessary for the activation of the cells above

There is lots of cross over between the two "divisions" of the immune system, including NK cells and dendritic cells.