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  • 1. LYMPHOID ORGANS Assoc. Prof. Dr. Karim Al-Jashamy MSU/IMS 2010
  • 2. Lymphoid Tissue  Lymphoid tissue is CT with rich supply of lymphocytes  Exists free within regular CT or is surrounded by capsules.  Very little cytoplasm so stain dark blue with H&E.  Rich network of reticular fibrils produced by fibroblast whose many processes rest on fibrils.
  • 3. Lymphatic System
  • 4. Lymphatic Capillaries
  • 5. Lymph Node
  • 6. Structure of Lymph Node
  • 7. Lymph Nodes  Functions include:  Filtration of particles and microorganisms to keep them out of general circulation.  Interaction of circulating antigens in lymph with lymphocytes to initiate immune response.  Activation, proliferation of B lymphocytes and antibody production.  Activation, proliferation of T lymphocytes.
  • 8. Cells of Lymph Node  Lymphoid cells  Macrophages and other phagocytic antigen processing cells  Lymphatic and vascular endothelial cells and fibroblasts responsible for lymph node supporting framework.
  • 9. Lymph Node
  • 10. Section of a lymph node showing the cortex and the medulla 1 Capsule; 2 lymphoid nodule with germinative center, Trabecula subcapsular sinus; (4) intermediate sinus; (5) medullary cords; (6) medullary sinus; (7) trabecula. (
  • 11. Medulla of Lymph Node Lymphocytes predominate Medullary sinuses Medullary cords
  • 12. LYMPH NODE Stained with H&E 1 - cortex 2 - paracortical zone 3 - medulla 4 - medullary cords 5 - lymphoid follicle of the cortex 6 - capsule 7 - subcapsular sinus 8 - cortical sinus 9 - medullary sinus
  • 13. Medullary sinus of a lymph node containing reticular cells with long processes and elongated nuclei, macrophages, and many lymphocytes. (1) Macrophage; (2) reticular cell; (3) trabecula. H&E stain. High magnification.
  • 14. Spleen  Largest accumulation of lymphoid tissue  Abundant phagocytic cells—defense against antigens in blood  Site of destruction of aged erythrocytes.  Production site of activated lymphocytes which are delivered to the blood.  THUS, an important blood filter and antibody- forming organ.
  • 15. Spleen
  • 16. Spleen
  • 17. Spleen
  • 18. Lymphoid Nodule 1. Germinative Center 2. Central artery
  • 19. Tonsil
  • 20. Tonsils are lymphoid structures located in the mucosa of the tongue, palate, and pharynx which provide sites where immune surveillance cells (lymphocytes) can encounter foreign antigens enter the body through the mouth or nose. Each tonsil consists of an epithelial crypt (invaginated pocket) surrounded by dense clusters of lymph nodules, each with a germinal center where lymphocytes proliferate.  The nodules are embedded in a mass of diffuse lymphoid tissue that consists of lymphocytes migrating to and from the germinal centers.
  • 21. The epithelium lining the crypt corresponds with that on the adjacent surface -- stratified squamous in the tongue and palate, or Pseudostratified Columnar in the pharynx. In either case, the epithelium may be heavily infiltrated with lymphocytes, and the crypt may be filled with lymphocytes and other debris
  • 22. PALATINE TONSIL 1 - lymphoid follicle 2 - diffuse lymphoid tissue 3 - crypt 4 - epithelium of the oral cavity musosa 6 - submucosa of the inner cover of oral cavity forms hemi-capsule of the tonsil
  • 23. Thymus
  • 24. THYMUS (lobule) H&E 1 - cortex 2 - medulla 3 - Hassal's corpuscle 4 - interlobular connective tissue (septa)