Lymphatic System

• Lymphatic system


  Consists of lymph, lymphatic vessels, several structures including organs containing lymphatic tissue, such as spleen, thymus, lymph nodes, lymph nodules, and red bone marrow
• Lymphatic tissue


  Specialized form of reticular connective tissue that contains large numbers of lymphocytes
• Lymphatic vessels


  1. Lymphatic capillaries merge to form larger lymphatic vessels, which ultimately drain into the thoracic duct or right lymphatic duct

  2. Thoracic duct empties its lymph into the left internal jugular and left subclavian veins

  3. Right lymphatic duct empties its lymph into the right internal jugular and right subclavian veins
• The thoracic duct drains a much larger portion of the body than does the right lymphatic duct
• Lymph


  Fluid that bathes the cells of body tissues, chemically similar to blood plasma
• Primary functions of the lymphatic system

  • Drains excess interstitial fluid
  • Transports dietary lipids
  • Carries out immune responses
• Lymph nodes


  • Masses of B cells and T cells surrounded by a capsule, lymph flows through them
• Flow of lymph


  1. Respiratory pump - during inspiration, flow of lymph increases as the thoracic cavity's pressure becomes more negative

  2. Skeletal muscle pump - when muscles contract, the valves are forced open to increase the lymph flow
• Primary lymphatic organs


  • Red bone marrow
  • Thymus
• Red bone marrow


  Site where stem cells divide and develop into mature B cells and T cells
• Thymus


  Site where immature T cells mature into functional T cells
• Secondary lymphatic organs and tissues

  • Lymph nodes
  • Spleen
  • Lymphatic nodules
• Lymph nodes


  • Located along lymphatic vessels, contain B cells, T cells, dendritic cells, and macrophages
• Lymphatic nodules


  • Egg-shaped masses of lymphatic tissue not surrounded by a capsule, plentiful in mucous membranes
• Spleen


  • Largest single mass of lymphatic tissue, contains white pulp (lymphatic tissue) and red pulp (blood-filled sinuses)
• Tonsils


  Pair of soft tissue masses located at the rear of the throat, composed of tissue similar to lymph nodes, contain crypts
• Innate immunity


  Defenses present at birth, includes physical and chemical barriers, antimicrobial substances, phagocytes, natural killer cells, inflammation, and fever
• Adaptive immunity


  Defenses involving specific recognition of a microbe, involves lymphocytes (T cells and B cells)
• Antimicrobial substances in body fluids

  • Interferons
  • Complement system
  • Iron-binding proteins
  • Antimicrobial proteins
• Inflammation


  • Nonspecific defensive response to tissue damage, characterized by pain, redness, and heat
• Fever is an elevated body temperature that intensifies the effects of interferons, inhibits the growth of some microbes, and speeds up body reactions that aid repair
• First line of defense: Skin and mucous membranes

  • Physical factors: Epidermis of skin, mucous membranes, mucus, hairs, cilia, lacrimal apparatus, saliva, urine, defecation and vomiting
  • Chemical factors: Sebum, lysozyme, gastric juice, vaginal secretions
• Second line of defense: Internal defenses

  • Antimicrobial substances: Interferons, complement system, iron-binding proteins, antimicrobial proteins
  • Natural killer cells
  • Phagocytes
  • Inflammation
  • Fever
• Antigen


  Any substance (foods, microbes, drugs, pollen, etc.) that the immune system recognizes as foreign (non-self)
• Cell-mediated immunity


  Cytotoxic T cells directly attack invading antigens
• Antibody-mediated immunity


  B cells transform into plasma cells, then into antibodies
• Antibodies


  Plasma proteins called immunoglobulins, grouped into five different classes
• Fever


  Initiates tissue repair; intensifies effects of interferons; inhibits growth of some microbes; speeds up body reactions that aid repair
• Copyright ©2018 John Wiley & Sons, Inc.
• Adaptive Immunity


  Involves the production of specific types of cells or specific antibodies to destroy a particular antigen
• Antigens


  • Large complex molecules, such as proteins, glycoproteins and lipoproteins
• B cells


  Lymphocytes involved in adaptive immunity
• T cells


  Lymphocytes involved in adaptive immunity
• Antibody


  Plasma proteins called immunoglobulins
• Classes of Immunoglobulins


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


  • About 80% of all antibodies in the blood; also found in lymph and the intestines; protects against bacteria and viruses by enhancing phagocytosis, neutralizing toxins, and triggering the complement system; only class of antibody to cross the placenta from mother to fetus, conferring considerable immune protection in newborns
• IgA


  • About 10-15% of all antibodies in the blood; found mainly in sweat, tears, saliva, mucus, breast milk, and gastrointestinal secretions; provides localized protection against bacteria and viruses on mucous membranes
• IgM


  • About 5-10% of all antibodies in the blood; also found in lymph; first antibody class to be secreted by plasma cells after an initial exposure to any antigen; activates complement and causes agglutination and lysis of microbes
• IgD


  • About 0.2% of all antibodies in the blood; also found in lymph and on the surfaces of B cells as antigen receptors; involved in activation of B cells
• IgE


  • Less than 0.1% of all antibodies in the blood; also located on mast cells and basophils; involved in allergic and hypersensitivity reactions and provides protection against parasitic worms