Lymphoid System By Yapa Wijeratne


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Presentation on the Overview of lymphoid system including histology slides. This will be useful for everyone those who are interested in & specially for self reviewing.

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Lymphoid System By Yapa Wijeratne

  1. 1. HistologyLymphoid System<br />by Yapa Wijeratne<br />Faculty of Medicine<br />University of Peradeniya<br />Sri Lanka<br />
  2. 2. You have two types of blood cells:<br />1. Red Blood Cells <br />(we call these 'Erythrocytes')<br />2. White Blood Cells <br />(we call these 'Leukocytes')<br />
  3. 3. Erythrocytes<br />These are pretty straight forward. Look at the Erythroid Series. <br />Leukocytes<br />The leukocytes are part of our immune defense system.<br />There are three types of leukocytes:<br />1. Granulocytes (These are also called 'Myeloid Cells.')<br />2. Monocytes<br />3. Lymphocytes<br />Some sources combine the monocytes and lymphocytes into one category and just call them all<br />'mononuclear leukocytes.' <br />
  4. 4. Granulocytes inlcude the <br />neutrophils, <br />eosinophils, and <br />basophils. <br />(It shouldn't surprise you to learn that their cytoplasm is often filled with granules.) <br />These are the work horses of acute inflammation (and other processes). <br />
  5. 5. In pathology and immunology, you'll call neutrophil, the PMN (polymorphonuclear leukocyte). <br />Eosinophils are involved in <br />allergic reactions & <br />parasitic infections. <br />
  6. 6. Mast Cell<br />Another cell to mention here (although it is NOT a granulocyte) is the Mast Cell. <br />It's very similar to the basophil: <br />both release histamine (and other mediators).<br />Some think that the mast cell is derived from the basophil. <br />Just remember that the basophil circulates and the mast cell is found in peripheral tissues. <br />Other than that, they are quite similar.<br />
  7. 7. Monocytes include the monocyte and the macrophage. <br />The monocyte circulates in the blood until it receives the signal to extravasate into the peripheral tissue. <br />Once in the tissue, it matures into the macrophage. It can also mature even further into other cells, but that is beyond the scope of this course. <br />The monocyte/macrophage is the work horse of chronic inflammation.<br />
  8. 8. Lymphoctyes are often overlooked when we consider blood, but they are white blood cells.<br />Indeed, they originate in the bone marrow and are derived from the same stem cell as the rest of the erythrocytes and leukocytes.<br />These are the T-cells and B-cells that direct the immune system and produce antibodies, respectively. <br />They are the central cells in our cell-mediated and humoral (antibody) defense mechanisms. <br />Also keep in mind that the B-cell can mature into the plasma cell.<br />
  9. 9. If you remember nothing else... Know that as a rule of thumb, <br />bacterial infections cause granulocytosis and <br />viral infections cause lymphocytosis. <br />There are exceptions to this, but this is a very basic (and important) concept. You'll learn more about why this is in immunology.<br />Spend some time learning the pathways from the original stem cell and realize that it gives rise to all these cells<br />
  10. 10. Infant Thymus<br />The lobules of the infant thymus are separated by connective tissue septa.<br />
  11. 11. Infant Thymus<br />Notice that the medulla (M) tends to stain lighter than the cortex (C).<br />
  12. 12. Hassall's Corpuscles<br />The thymus has no germinal centers like many other lymphoid tissues, <br />but it does have distinguishing Hassall's corpuscles (arrows) comprised of multiple layers of epitheloid cells.<br />
  13. 13. Adult Thymus<br />The post-pubescent thymus involutes and is characterized by areas of adipose tissue (A).<br />
  14. 14. Palatine Tonsil<br />The palatine tonsil is partially encapsulated in connective tissue. <br />Look for the lighter-stained germinal centers (GC).<br />
  15. 15. Pharyngeal Tonsil<br />The pharyngeal tonsil is distinguished from the palatine by <br />the presence of pseudostratified columnar epithelium (arrows).<br />
  16. 16. Peyer's Patch<br />Don't forget the GI tract! The Peyer's Patches are visible with the naked eye. Notice the germinal center where B-cells proliferate. <br />These are a major source of antibody production. <br />
  17. 17. Appendix<br />The vermiform appendix houses a large number of lymphocytes and lightly-stained germinal centers.<br />
  18. 18. Spleen<br />The distinctive red pulp (RP) and white pulp (WP) identify the spleen. <br />No you're not color blind ... histologists call that blue tissue "white". (Now that you know a little about the immune system, can you guess why?)<br />
  19. 19. Spleen<br />The red pulp (RP) is composed of open sinusoids containing blood. The white pulp (WP) contains lymphocytes.<br />
  20. 20. Lymph Node<br />The lymph node filters both lymph and blood. Lymph enters the subcapsular sinuses (SS) and exits the hilar region whereas blood both enters and exits.<br />
  21. 21. Lymph Node<br />Find the germinal centers in the darkly stained cortex. <br />Notice also the connective tissue capsule that surrounds the node.<br />
  22. 22. Lymph Node<br />Lymph first enters the sub-capsular sinus (SS) and then percolates through various trabeculae (T) to the medulla.<br />
  23. 23. Lymph Node<br />Once in the medulla, lymph is channeled through medullary cords (MC) to the hilum.<br />
  24. 24. Plasma Cells<br />Don't forget that plasma cells are derived from B lymphocytes. <br />These cells are antibody factories. <br />They produce thousands of antibodies per second for a few days and then they die.<br />
  25. 25. Note:<br /> This presentation was prepared using photographs & content from various web sites & textbooks on the assumption of fair usage for studying (specially teaching & self reviewing ) & is for NON-COMMERCIAL purposes.<br />