Lymphatics

• Lymphatic tissues


  Found in the mucosa (lamina propia) of the respiratory tract, digestive tract, appendix, and all lymphoid organs
• Lymphatic tissues


  • Parenchyma: lymphocytes
  • Stroma: reticular tissue (reticular cells and reticular fibers)
  • Plasma cells
  • Macrophages
  • Neutrophils
  • Eosinophils
• Antigenic determinant


  Responsible for the specificity of the antigen-antibody reaction
• Immune response


  A specific defensive reaction of cells of the immune system against macromolecules
• Lymphocytes


  • Small spherical or oval cells
  • Large rounded nucleus, or slightly indented on one side
  • Narrow, non-granular cytoplasm
• Lymphocytes play a vital role in the initiation of immune response
• Types of lymphocytes


  • B lymphocytes
  • T lymphocytes
• B lymphocytes


  Responsible for specific immunoglobulin and antibody production<|>Small lymphocytes serve as memory cells<|>Secondary response
• T lymphocytes


  Mediate cell-mediated immunity<|>Delayed-type of hypersensitivity reactions<|>Against neoplastic cells<|>Mediate graft vs host reactions<|>Immunologic memory
• Classification of lymphatic tissue

  • Diffuse lymphatic tissue
  • Nodular lymphatic tissue
• Dense lymphatic tissue


  • Lymphocytes are abundant and closely packed together
  • Found in the lamina propia of the lower respiratory tract and lower digestive tract
• Loose lymphatic tissue


  • Lymphocytes are few and irregularly scattered in a loose manner
  • Found in the lamina propia of the upper respiratory tract and upper alimentary tract
• Nodular lymphatic tissue


  • Compact circumscribed aggregations of lymphocytes forming lymphatic follicle or lymphatic nodules
  • Not permanent structures
  • With or without germinal center
• Germinal center


  Central, pale staining portion of a lymphatic nodule<|>Contains follicular dendritic cells<|>Composed of bigger lymphocytes
• Lymphatic organs


  • Primary: Thymus
  • Secondary: Spleen, lymph node, Peyer's patches, tonsils
• Thymus


  • Located in the supero-anterior mediastinum
  • 2 lobes
  • Capsulated, septated
  • No germinal center
  • Contains lymphocytes and epithelial reticular cells
• Thymic cortex


  Peripheral zone of dense lymphatic tissue<|>Contains thymocytes
• Thymic medulla


  Lightly staining central zone of loose connective tissue<|>Contains fully mature T cells
• Thymus function


  Cell-mediated immunity<|>Humoral immunity
• Role of thymus in T cell maturation

  T lymphoblast (from fetal liver or bone marrow) -> Thymus -> Mature thymocytes with T cell marker -> Thymic selection
• Lymph node


  • 2-10 mm in diameter
  • Encapsulated kidney-shaped or bean-shaped organs along the course of lymphatic vessels
  • Widely distributed throughout the body
• Lymph node structure


  • Capsule: dense connective tissue
  • Trabeculae
  • Stroma: reticular tissue
  • Contains lymphocytes, plasma cells, macrophages, dendritic cells
• Lymph node cortex


  Outer, dense staining portion
• Lymph node medulla


  Inner, paler staining portion
• Lymph node cortex


  • Appears as a dense mass of lymphoid cells
  • Traversed by collagenous trabeculae and cortical sinuses
  • Composed of lymphatic nodules (formed mainly by B lymphocytes)
• Subcapsular sinuses


  Located beneath the capsule
• Thymus


  • Function in T cell maturation
• T cell maturation


  T lymphoblast (fetal liver or bone marrow) -> Thymus -> Mature thymocytes with T cell marker -> Thymic selection
• Lymph node


  1. 10 mm in diameter, encapsulated kidney-shaped or bean-shaped organs along the course of lymphatic vessels, widely distributed throughout the body
• Lymph node structure


  • Capsule - dense connective tissue
  • Trabeculae
  • Stroma - reticular tissue
  • Lymphocytes
  • Plasma cells
  • Macrophages
  • Dendritic cells - within lymphoid nodule
• Lymph node medulla


  Inner paler staining portion
• Lymph node cortex


  • Appears as a dense mass of lymphoid cells, traversed by collagenous trabeculae and cortical sinuses, composed of lymphatic nodules (formed mainly by B lymphocytes)
• Lymph node cortical sinuses

  • Located between lymphoid nodules
• Lymph node paracortex


  • Lacks B cell lymphoid nodules, presence of T cells
• Lymph node medulla components

  • Medullary cords
  • Medullary sinuses
• Lymph node medullary cords

  • Branched cord-like extensions consisting of B lymphocytes, plasma cells, macrophages
• Lymph node medullary sinuses


  • Spaces between medullary cords, contain reticular cells and fibers, lymph, lymphocytes, macrophages, granulocytes, continuous with the cortical sinuses
• Lymphatic sinuses


  • Subcapsular or Marginal sinus
  • Cortical or Intermediate sinus
  • Medullary Sinus
• Functions of lymph nodes

  • Filtration of lymph, provides lymph with lymphocytes, immunological defense of the body (humoral and cellular immune response)
• Spleen


  Largest lymphoid organ in the body, located in the left hypochondriac, encapsulated, with fibrous trabeculae and reticular tissue stroma