Lympathic System

• Lymphatic system


  Consists of lymphatic vessels and lymphoid tissues/organs
• Function of lymphatic vessels

  1. Pick up excess interstitial fluid (lymph)

  2. Return lymph to the blood
• Lymphatic vessels


  • Form a one-way system
  • Lymph flows only toward the heart
• Lymph nodes


  • Remove foreign material from lymphatic stream
  • Produce lymphocytes for immune response
• Swollen "glands" during infection are actually swollen lymph nodes
• Body defense mechanisms


  • Innate
  • Adaptive
• Innate defense system


  Responds immediately to protect the body from all foreign substances
• Adaptive defense mechanism


  Fights invaders that get past the innate defenses by mounting an attack against particular foreign substances
• Immune system


  • Protects from bacteria, viruses, transplanted organs/grafts, and cancer cells
  • Acts directly by cell attack and indirectly by releasing chemicals and antibodies
• Aspects of adaptive defense

  • Antigen specific
  • Systemic
  • Has "memory"
• Humoral immunity


  Provided by antibodies present in body fluids
• Cellular immunity


  Provided by lymphocytes defending the body
• Antigen


  Any substance capable of provoking an immune response
• Lymphocytes


  • B cells produce antibodies and oversee humoral immunity
  • T cells constitute cell-mediated arm of adaptive defenses
• Antigen-presenting cells (APCs)


  Engulf antigens and present fragments on their surface for recognition by T cells
• The adaptive immune system uses lymphocytes, APCs, and specific molecules to identify and destroy all substances in the body that are not recognized as self
• B cell


  Lymphocyte that matures in the bone marrow
• T cell


  Lymphocyte that matures in the thymus
• Lymphocyte maturation


  1. Migrate to thymus or bone marrow

  2. Undergo maturation process

  3. Immature lymphocytes divide rapidly

  4. Only those with ability to identify foreign antigens survive

  5. Lymphocytes capable of binding with self-antigens are destroyed
• B cell maturation in bone marrow is less understood
• Immunocompetent lymphocyte


  Able to react to one and only one distinct antigen
• Major types of APCs

  • Dendritic cells
  • Macrophages
  • B lymphocytes
• Adaptive immune system


  • Two-fisted defense system with humoral and cellular arms
  • Uses lymphocytes, APCs, and specific molecules to identify and destroy substances not recognised as self
• Adaptive immune response


  1. Cells recognise foreign substances (antigens)

  2. Cells communicate to mount a response specific to those antigens
• B cell activation


  1. Antigen binds to B cell surface receptors

  2. B cell undergoes cloning selection

  3. B cell clone members become plasma cells or memory cells
• Active immunity


  Acquired during infections or through vaccination, where B cells produce antibodies
• Passive immunity


  Obtained from antibodies in serum of immune donor, does not involve B cell activation
• Antibodies


  Soluble proteins secreted by activated B cells or plasma cells in response to an antigen
• Ways antibodies inactivate antigens

  • Complement fixation
  • Neutralization
  • Agglutination
  • Opsonization
  • Precipitation
• Cellular (cell-mediated) immune response

  T cells fight antigens directly, unlike B cells which secrete antibodies
• T cell activation


  1. Antigen must be presented by APC

  2. Helper T cells and cytotoxic T cells are involved

  3. Regulatory T cells suppress immune response after antigen is destroyed
• Most T cells enlisted in a response die within days, but memory cells remain
• The most important disorders of the immune system are allergies, autoimmune diseases, and immunodeficiencies
• Allergies


  Abnormally vigorous immune responses causing tissue damage
• Types of allergies


  • Immediate hypersensitivity (acute)
  • Anaphylactic shock
• Autoimmune disease


  Immune system attacks its own tissues
• Examples of autoimmune diseases

  • Rheumatoid arthritis
  • Myasthenia gravis
  • Multiple sclerosis
  • Graves' disease
  • Type 1 diabetes
  • Systemic lupus erythematosus
  • Glomerulonephritis
• Immunodeficiencies


  Congenital or acquired conditions with abnormal immune cell production or function
• Severe combined immunodeficiency disease (SCID) is a devastating congenital immunodeficiency
• Acquired immune deficiency syndrome (AIDS) cripples the immune system by interfering with helper T cell activity