Lymphatic system

• Functions of the lymphatic system


  • Fluid balance
  • Fat absorption
  • Defense
• Components of the lymphatic system

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


  • Carry fluid in one direction from tissues to circulatory system
  • Fluid moves from blood capillaries into tissue spaces
  • Tiny, closed-ended vessels
  • Fluid moves easily into capillaries
  • In most tissues
  • Join to form lymphatic vessels
• Lymphatic vessels


  • Resemble small veins
  • Where lymphatic capillaries join
  • One-way valves
• Right lymphatic duct


  1. Where lymphatic vessels from right upper limb and right head, neck, chest empty

  2. Empties into right subclavian vein
• Thoracic duct


  1. Collects lymph from the from remaining lymphatic vessels which do not enter the right lymphatic duct

  2. Empties into left subclavian vein
• Tonsils


  • Palatine tonsils on each side of oral cavity
  • Pharyngeal tonsils near internal opening of nasal cavity (adenoid)
  • Lingual tonsils posterior surface of tongue
  • Form a protective ring of lymphatic tissue around nasal and oral cavities
• Lymph nodes


  • Rounded structures that vary in size
  • Located near lymphatic vessels
  • Groin, armpit, neck
  • Lymph passes through lymph nodes before entering blood
  • Lymph moves through and immune system is activated (lymphocytes produced) if foreign substances are detected
  • Removes microbes by macrophages
• Spleen


  • Size of clenched fist
  • Located in abdomen
  • Filters blood
  • Detects and responds to foreign substances
  • Destroys old red blood cells
  • Serves as a blood reservoir
  • White pulp: lymphatic tissue surrounding arteries
  • Red pulp: contains macrophages and red blood cells that connect to veins
• Thymus gland


  • Bilobed gland
  • Located in mediastinum behind the sternum
  • Stops growing at age 1
  • At age 60 decreases in size
  • Produces and matures lymphocytes
• Immunity


  The ability to resist damage from foreign substances
• Types of immunity


  • Innate
  • Adaptive
• Innate immunity


  • Present at birth
  • Defense against any pathogen
  • Accomplished by physical barriers, chemical mediators, white blood cells, and inflammatory response
• Physical barriers in innate immunity

  • Skin and mucous membranes
  • Tears, saliva, urine
• Chemical mediators in innate immunity

  • Lysozyme
  • Mucous membranes
  • Histamine
  • Interferons
• Cells of the immune system

  • Phagocytic cells (neutrophils, macrophages)
  • Eosinophils
  • Basophils
  • Mast cells
  • Natural killer cells
• Inflammatory response


  • Involves chemicals and cells produced due to injury
  • Signaled by presence of foreign substance
  • Stimulates release of chemical mediators
• Adaptive immunity


  • Acquired after birth
  • Reacts when innate defenses don't work
  • Slower than innate immunity
  • Has memory
  • Uses lymphocytes (B and T cells)
  • 2 types: antibody-mediated and cell-mediated
• Antigen


  Substance that stimulates an immune response
• Self-antigen


  Molecule produced by the person's body that stimulates an immune system response
• Antibody


  Proteins the body produces in response to an antigen
• Stem cells


  • Live in red bone marrow
  • Give rise to all blood cells
  • Give rise to some pre-T cells and pre-B cells
• Lymphocytes


  • Type of white blood cell
  • Involved in adaptive immunity
  • Develop from stem cells
  • Differentiate into specific lymphocytes such as B or T cells
• B cells


  • Type of lymphocytes
  • Involved in antibody-mediated immunity
  • Originate from stem cells
  • Mature in red bone marrow
  • Move to lymphatic tissue after maturing
  • Lead to production of antibodies
• T cells


  • Type of lymphocyte
  • Involved primarily in cell-mediated immunity but also participate in antibody-mediated immunity
  • Mature in thymus gland
  • Move to lymphatic tissue after maturing
  • 4 types
• Antigen recognition


  • Lymphocytes have antigen receptors on their surface
  • Called B-cell receptors on B cells and T-cell receptors on T cells
  • Each receptor only binds with a specific antigen
  • When antigen receptors combine with the antigen, the lymphocyte is activated, and adaptive immunity begins
• MHC molecule


  • Contains binding sites for antigens
  • Specific for certain antigens
  • Hold and present a processed antigen on the surface of the cell membrane
  • Bind to antigen receptor on B or T cells and stimulate response
• Cytokines


  Proteins secreted by a cell that regulates neighboring cells
• Proliferation of helper T cells

  1. After antigen is processed and presented to helper T cells, helper T cells produce interleukin-2 and interleukin 2-receptors

  2. Interleukin-2 binds to receptors and stimulates more helper T cell production

  3. Helper T cells are needed to produce B cells

  4. B cells produce antibodies
• Dual nature of the immune system

  • Lymphocytes give rise to 2 types of immune responses: antibody-mediated and cell-mediated
  • Antigens can trigger both types of responses
  • Both types are able to recognize self-versus non-self, use specificity, and have memory
• Antibody-mediated immunity


  • Effective against antigens in body fluids (blood and lymph)
  • Effective against bacteria, viruses, toxins
  • Uses B cells to produce antibodies
• Antibody structure


  • Letter Y shape
  • Variable region: V of Y, bind to epitopes of antigen using antigen-binding site
  • Constant region: stem of Y, each class of immunoglobulin has same structure
  • Antigen-binding site: site on antibody where antigen binds
  • Valence: number of antigen-binding sites on antibody
• Classes of immunoglobulins


  • IgG
  • IgM
  • IgA
  • IgE
  • IgD
• IgG


  • 80 to 85% in serum
  • Activates compliment and increases phagocytosis
  • Can cross the placenta and provide protection to the fetus
  • Responsible for Rh reactions, such as hemolytic disease of the newborn
• IgM


  • 5 to 10% in serum
  • Activates compliment
  • Acts as an antigen binding receptor on the surface of B cells
  • Responsible for transfusion reactions in the ABO blood system
  • Often the first antibody produced in response to an antigen
• IgA


  • 15% in serum
  • Secreted into saliva, into tears, and onto mucous membranes
  • Protects body surfaces
  • Found in colostrum and milk to provide immune protection to the newborn
• IgE


  • 0.002% in serum
  • Binds to mast cells and basophils and stimulates the inflammatory response
• IgD


  • 0.2% in serum
  • Functions as an antigen-binding receptor on B cells
• Effects of antibodies


  • Inactivate antigen
  • Bind antigens together
  • Active complement cascades
  • Initiate release of inflammatory chemicals
  • Facilitate phagocytosis
• Antibody production


  1. Primary response: 1st exposure of B cell to antigen, B cell undergoes division and forms plasma cell and memory cells

  2. Secondary response: when immune system is exposed to antigen that has been seen before, memory B cells quickly divided to form plasma cells which produce antibodies