lymphatic system chapter 24

• Lymphatic system


  Transports fluids and helps fight infections
• Excess interstitial fluid entering lymph vessels


  1. Fluid enters vessels

  2. Fluid is called lymph

  3. Lymph vessels return fluid to venous circulation

  4. If not removed it would accumulate and cause edema
• Lymph vessels


  Transport dietary lipids
• Lymphatic organs


  Aid in production and maturation of lymphocytes
• Lymphatic system


  Generates immune response against antigens
• Lymph flow through lymphatic network

  1. Lymphatic capillaries

  2. Lymphatic vessels

  3. Lymphatic trunks

  4. Lymphatic ducts
• Lymphatic capillaries


  • Closed-ended tubes interspersed among most blood capillary beds
  • Not in red marrow or avascular tissues
  • Recently found to be in dural venous sinuses of brain
  • Resemble blood capillaries but have overlapping endothelial cells that act as one-way entry flaps
  • Gastrointestinal tract contains specialized lymph capillaries called lacteals
• Chyle


  Lymph collected from gastrointestinal system
• Lymph flow through lymph nodes


  1. Afferent lymphatic vessels bring lymph to a lymph node

  2. Efferent lymphatic vessels transport filtered lymph away from the lymph node
• Lymphatic trunks


  • Jugular trunks
  • Subclavian trunks
  • Bronchiomediastinal trunks
  • Intestinal trunks
  • Lumbar trunks
• Right lymphatic duct


  • Returns lymph at the junction of right subclavian and internal jugular veins
  • Returns lymph from the right side of the head and neck, right upper limb and the right side of the thorax
• Thoracic duct


  • Largest lymphatic vessel
  • Begins as cisterna chyli
  • Collects lymph from most of the body
  • Returns lymph into the junction between the left subclavian and internal jugular veins
• Lymphatic cells


  • Macrophages
  • Nurse cells
  • Dendritic cells
  • Lymphocytes
• Types of lymphocytes


  • T-lymphocytes (T-cells)
  • B-lymphocytes (B-cells)
  • Natural killer (NK) cells
• 1. lymphocytes


  • Make up 70-85% of body lymphocytes
  • Express a plasma membrane coreceptor that can recognize a particular antigen
  • Include helper T-lymphocytes and cytotoxic T-lymphocytes
• 1. lymphocytes


  • Make up 15-30% of body lymphocytes
  • Contain antigen receptors to only one antigen
  • Stimulate production of immunoglobulin or antibodies against that antigen
  • Activated by helper T-lymphocytes
  • Most become plasma cells that produce and secrete large amounts of antibodies
  • Some become memory B-lymphocytes and confer immunity to certain antigens for many years or a lifetime
• NK cells


  • Also called large granular lymphocytes
  • Relatively small percentage of all lymphocytes
  • Unlike T-cells and B-cells, can kill a wide variety of infected cells and some cancerous cells
• Lymphopoiesis


  1. Process of lymphocyte development

  2. All lymphocyte types originate in red bone marrow but their maturation sites differ

  3. Final result is that lymphocyte becomes Immunocompetent
• Lymphatic nodules


  • Clusters of lymphatic cells with some extracellular matrix but without a connective tissue capsule
  • Center is germinal center containing proliferating B-lymphocytes and macrophages
  • T-lymphocytes located outside the germinal center
  • Filter and attack antigens
• MALT


  • Mucosa associated lymphatic tissue consisting of lymphatic nodules within the mucosa of the gastrointestinal, respiratory, genital, and urinary tracts
  • Very prominent in the ileum as Peyer patches
• Tonsils


  • Large clusters of lymphatic cells and matrix located mainly in the pharynx
  • Pharyngeal tonsils (adenoids) in the posterosuperior wall of the nasopharynx
  • Palatine tonsils in the posterolateral wall of the oral cavity
  • Lingual tonsils along the posterior one-third of the tongue
  • Form crypts for trapping of antigens - facilitates antigen identification by lymphocytes
• Main lymphatic organs


  • Thymus
  • Lymph nodes
  • Spleen
• Thymus


  • Bilobed organ located superficial to the heart
  • Consists of two fused thymic lobes, divided into lobules by connective tissue trabeculae
  • Each lobule has an outer cortex and an inner medulla
  • Continues to grow until puberty and then begins to regress in size and function
  • Site of T-lymphocyte differentiation and maturation
  • In adulthood, T-lymphocytes can only be produced by cell division and not by the maturation of new cells in the thymus
• Lymph nodes


  • Small, oval structures located along the pathway of lymph vessels
  • Typically found in clusters
  • Surrounded by a tough connective tissue capsule
  • Internal extensions of the capsule, trabeculae, project inwards
  • Lymphatic cells surround the trabeculae and lymphatic sinuses provide a pathway for lymph flow
  • Divided into outer cortex and inner medulla
  • Cortex consists of nodules and sinuses called cortical sinuses
  • Medulla contains medullary cords and medullary sinuses
  • Afferent vessels deliver lymph to the node
  • Lymph exits nodes via efferent vessels at an indentation of the node called the hilum
• Spleen


  • Largest lymphatic organ in body just lateral to left kidney
  • Surrounded by a dense irregular connective tissue capsule, which sends extensions called trabeculae into the organ
  • White pulp is associated with the arterial supply and consists of clusters T-cells, B-cells, and macrophages
  • Red pulp is associated with the venous supply and consists of splenic cords and splenic sinusoids containing erythrocytes, platelets, macrophages, and some plasma cells
  • Functions include initiating immune response when antigens are found in blood, serving as a reservoir for erythrocytes and platelets, phagocytizing old/defective erythrocytes and platelets, and phagocytizing bacteria and other foreign materials