Lymphatic system

• Functions of the Lymphatic System

  • Fluid balance
  • Lipid absorption
  • Protection – immune surveillance
• Structures of the Lymphatic System

  • Lymph
  • Lymphocytes
  • Lymphatic vessels
  • Lymph nodes
  • Tonsils
  • Spleen
  • Thymus

  
• Primary Lymphoid Organs


  • Include thymus gland and bone marrow
  • Produce lymphocytes

  
• Secondary Lymphoid Organs


  Include the lymph nodes, the spleen, and diffuse lymphoid tissue found in the mucosa of the digestive system, including the tonsils, Peyer patches, and appendix

  
• Immunity


  The immune system refers to a collection of cells and proteins that function to protect the body from foreign antigens, such as microbes, viruses, cancer cells, and toxins
• 2 TYPES OF IMMUNITY

  • INNATE IMMUNITY
  • ADAPTIVE IMMUNITY (Acquired immunity)
• INNATE IMMUNITY


  • The first line of defense against an intruding pathogen
  • Non-specific and is immediately activated upon encountering an antigen
  • Has no immunologic memory
• ADAPTIVE IMMUNITY


  • Antigen-dependent and antigen-specific
  • There is a lag time between exposure to the antigen and maximal response
  • Has memory, therefore upon subsequent exposure to the same kind of antigen immune response becomes more rapid and efficient
• FIRST LINE OF DEFENSE


  • Physical and chemical barriers
• PHYSICAL AND MECHANICAL BARRIERS

  • SKIN
  • MUCOUS MEMBRANES
• CELLULAR AND CHEMICAL FACTORS


  • Tears and saliva contain lysozyme
  • Gastric acids: The acidity of the stomach kills most invading organisms that are swallowed and take up residence there
• MICROBIAL ANTAGONISM


  The indigenous microflora prevents other microorganisms from colonizing a particular anatomic part of the body
• COMPONENTS OF THE SECOND LINE OF DEFENSE

  • TRANSFERRIN
  • FEVER
  • INTERFERONS
  • COMPLEMENT SYSTEM
  • INFLAMMATION
  • PHAGOCYTOSIS
  • CHEMOTAXIS
• TRANSFERRIN


  A glycoprotein synthesized in the liver that stores and delivers iron to host cells thereby depriving pathogens of iron
• FEVER


  • Pyrogens are substances that stimulate fever
  • Pyrogens may come from outside the body (pathogens) or inside the body (interleukins)
  • These substances raise the hypothalamic set point which triggers vasoconstriction and shunting of blood from the periphery to decrease heat loss
• Effects of Fever


  • Stimulates leukocytes to destroy invaders
  • Reduces free plasma iron
  • Induces production of interleukin 1
  • Slows down rate of growth of certain pathogens
• INTERFERONS


  Antiviral proteins produced by virus-infected cells that interfere with viral replication
• COMPLEMENT SYSTEM


  A biochemical cascade of the immune system that helps clear pathogens from an organism, and promote healing

  
• INFLAMMATION


  • The local response of vascularized living tissue to injury
  • Its aim is to eliminate the initial cause of cell injury as well as necrotic cells and tissues resulting from the injury
• SEQUENCE OF EVENTS IN INFLAMMATION

  1. tissue injury

  2. vasodilation

  3. increased permeability

  4. emigration of leukocytes

  5. chemotaxis

  6. phagocytosis
• CARDINAL SIGNS OF INFLAMMATION

  • Redness (rubor)
  • Calor (heat)
  • Swelling (tumor)
  • Pain (dolor)
  • Impairment of function (function laesa)
• PHAGOCYTOSIS


  A process by which particles, microbes or fragments of dead cells are engulfed and internalized, usually by specific membrane receptors
• PROFESSIONAL PHAGOCYTES


  • Neutrophils
  • Macrophages
• WANDERING MACROPHAGES


  Leave the blood stream and migrate to infected areas
• FIXED MACROPHAGES


  Remain in tissues and trap foreign debris. They are also called histiocytes
• CHEMOTAXIS


  Migration of phagocytes to the site of injury as a result of release of chemical attractants (chemotactic agents)

  
• THIRD LINE OF DEFENSE

  The adaptive immune response, which is specific and has memory

  
• ANTIGEN


  Specific substances found in foreign microbes, usually proteins, that serve as the stimulus to produce an immune response

  
• ANTIGENS


  • FOREIGN ANTIGEN
  • SELF-ANTIGENS
• T LYMPHOCYTES


  • HELPER T CELLS
  • CYTOTOXIC T CELLS
  • SUPPRESSOR T CELLS
  • MEMORY T CELLS
• HELPER T CELLS


  • When a pathogen invades the body, it is engulfed by wandering macrophages which present the antigenic fragments on its surface
  • This macrophage becomes an antigen-presenting cell, and presents the antigen to helper T cells
  • The TH cells bind to the antigen and become activated, and in turn activate the B cell with the specific antibody for the antigen
  • This B cell clones and differentiates into plasma cells and memory cells

  
• CYTOTOXIC T CELLS


  Recognize antigenic fragments on infected cells and kill these cells before the virus has time to replicate
• SUPPRESSOR T CELLS


  Once the infected cells have been destroyed, inhibit the TC cells, to ensure that normal cells are not subsequently attacked
• MEMORY T CELLS


  Remain dormant after the initial exposure to an antigen, and are stimulated to convert themselves into cytotoxic T cells and help fight the pathogen upon subsequent exposure
• IMMUNOLOGICAL MEMORY


  • When B and T cells divide and differentiate, a small proportion of clones will differentiate into memory cells
  • Memory cells remain in the body for many years
  • If a second infection with the same antigen occurs, the memory cells react faster and more vigorously than the initial immune response
• 2 types of Adaptive Immunity

  • CELL MEDIATED IMMUNITY
  • HUMORAL IMMUNITY

  
• CELL-MEDIATED IMMUNITY


  • Activation of humoral immunity by T helper cells and the targeted destruction of infected cells by cytotoxic T cells
  • Does not involve antibodies, rather involves the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, macrophages, NK cells, granulocytes and the release of various cytokines in response to antigen

  
• HUMORAL IMMUNITY


  Involves the production of antibodies by B lymphocytes

  
• B cells


  Antibody-producing cells that develop in the bone marrow to produce a highly specific antibody that recognizes one type of antigen
• ANTIBODY


  • A protein produced in response to an antigen
  • Also called " gamma globulin" or "immunoglobulin"
  • Structure: made up of 4 polypeptide chains (2 light and 2 heavy chains) joined together by disulphide bonds to form a Y-shaped molecule
  • The ends of the arms are where the antigens bind and these areas are called the variable regions, as these will differ between antibodies
  • An antibody recognizes a specific antigen only
  • Antibodies can be divided into five classes (IgM, IgG, IgA, IgD, and IgE) based on their physiochemical, structural, and immunological properties