Lymphatic System

• The lymphatic system and immunity

  
• Learning objectives


  • Name the functions of the lymphatic system
  • Explain what lymph is and how it forms
  • Describe lymph flow through the body
  • Name the principal lymphatic trunks
  • Describe the functions of the tonsils and spleen
  • Explain the unique role the thymus gland plays as part of the lymphatic system
  • Describe the different types of immunity
  • Explain the difference between blood and lymphatic capillaries
  • Explain the difference between active immunity and passive immunity
  • Define an antigen and an antibody

  
• Lymphatic capillaries


  • Begin as blind-end tubes next to tissue cells and blood capillaries
• Lymph nodes


  Oval to bean-shaped structures found along the length of lymphatics (lymph glands)

  
• Lymph node function


  1. Afferent lymphatic vessels enter the node

  2. Immune response is activated

  3. Lymphocytes are produced and released into the lymph

  4. Macrophages remove dead microorganisms and foreign substances

  5. Lymph is purified before reaching the veins

  6. Function as an early-warning defense system

  
• Thymus


  • Primary lymphoid organ necessary in early life immunity but later in life atrophies and becomes inactive
  • Produces hormones important for T cell development and maintenance

  
• Spleen


  • Contains the largest collection of lymphoid tissue in the body
  • Removes abnormal blood cells and other blood components
  • Stores iron recycled from red blood cells
  • Initiates immune responses by B cells and T cells

  
• Immunity


  Body's ability to resist and defend against infectious organisms or other substances that could damage tissues and organs

  
• Antigens


  Foreign proteins that gain access to our bodies
• Types of antibodies


  • IgG
  • IgM
  • IgA
  • IgD
  • IgE
• Innate immunity


  Physical barriers and internal defense processes that either prevent or slow the entry of infectious organisms, or attack them if they do enter

  
• Adaptive (specific) immunity


  Two classes of lymphocytes, T cells and B cells, respond to specific antigens

  
• Lymphocyte production


  1. Bone marrow

  2. Thymus

  3. Lymph nodes

  4. Spleen

  
• Immune system generally ignores the body's own cells unless they become abnormal

  
• Natural killer (NK) cells


  Responsible for recognizing and destroying abnormal cells in peripheral tissue

  
• Interferons


  Small proteins released by activated lymphocytes, macrophages, and infected tissue cells that trigger antiviral proteins in normal cells

  
• Cells for the immune response

  • B cells
  • Plasma cells
  • Helper T cells
  • Killer T cells
  • Suppressor T cells
  • Memory cells
  • Macrophages

  
• Chemicals for the immune response

  • Lymphokines
  • Monokines
  • Complement proteins

  
• Complement system activation


  1. Classical pathway

  2. Lectin pathway

  3. Alternative pathway
• Inflammation


  • Temporarily repairs injury, prevents additional pathogens, mobilizes defenses, facilitates regeneration
  • Mast cells release histamine and heparin
• Lymphocytes of adaptive immunity

  • B cells
  • T cells

  
• Active immunity


  Develops after exposure to an antigen, can be naturally or artificially acquired

  
• Passive immunity


  Produced by transferring antibodies from another source, can be naturally or artificially acquired