Understanding the Lymphatic System and Immunity: The Thymus and Spleen Functions

1. Chapter 22, part 2 The Lymphatic System and Immunity

2. The Thymus • Located behind sternum in anterior mediastinum • Capsule • Two lobes • Divided into lobules, each with a cortex and medulla • Cortical lymphocytes surrounded by reticular endothelial cells • Maintain blood–thymus barrier • Secretes thymic hormones: thymosins, thymopoietins, and thymulin

3. Figure 22.8 The Thymus Figure 22.8a-c

4. The Spleen • Largest mass of lymphoid tissue • Cellular components form pulp • Red pulp contains RBC • White pulp similar to lymphoid nodules • Spleen functions include • Removal of abnormal blood cells and other blood components • Storage of iron • Initiation of the specific immune response

5. Figure 22.9 The Spleen Figure 22.9a-c

6. Lymphatic system and body defenses • Nonspecific defenses • Do not distinguish one type of threat from another • 7 types • Specific defenses • Protect against particular threats • Depend upon the activation of lymphocytes

7. SECTION 22-3Nonspecific Defenses

8. Nonspecific Defenses, Physical barriers • Keep hazardous organisms outside the body • Includes hair, epithelia, secretions of integumentary and digestive systems

9. Figure 22.10 Nonspecific Defenses (Part 1 - Physical Barriers) Figure 22.10

10. Nonspecific Defenses, Phagocytes • Remove cellular debris and respond to invasion by foreign pathogens • Monocyte-macrophage system - Fixed and free • Microphages – Neutrophils and eosinophils • Move by diapedesis • Exhibit chemotaxis

11. Figure 22.10 Nonspecific Defenses(Part 2 - Phagocytes) Figure 22.10

12. Nonspecific Defenses, Immunological surveillance • Constant monitoring of normal tissue by NK cells • NK cells • Recognize cell surface markers on foreign cells • Destroy cells with foreign antigens

13. NK cell activation • Recognition of unusual surface proteins • Rotation of the Golgi toward the target cell and production of perforins • Release of perforins by exocytosis • Interaction of perforins causing cell lysis

14. Figure 22.10 Nonspecific Defenses(Part 3 - Immunological Surveillance) Figure 22.10

15. Figure 22.11 How Natural Killer Cells Kill Cellular Targets Figure 22.11

16. Nonspecific Defenses, Interferons (cytokines) • Small proteins released by virally infected cells • Trigger the production of antiviral proteins • Three major types of interferons are: • Alpha– produced by leukocytes and attract/stimulate NK cells • Beta– secreted by fibroblasts causing slow inflammation • Gamma – secreted by T cells and NK cells stimulate macrophage activity

17. Figure 22.10 Nonspecific Defenses(Part 4 - Interferons) Figure 22.10

18. Nonspecific Defenses, Complement system • Cascade of ~11 plasma complement proteins (C) • Destroy target cell membranes • Stimulate inflammation • Attract phagocytes • Enhance phagocytosis

19. Complement proteins interact with on another via two pathways • Classical • Alternative

20. Figure 22.10 Nonspecific Defenses(Part 5 - Complement System) Figure 22.10

21. Figure 22.12 Complement Activation Figure 22.12

22. Nonspecific Defenses, Inflammation • Localized tissue response to injury producing • Swelling • Redness • Heat • Pain • Effects of inflammation include • Temporary repair of injury • Slowing the spread of pathogens • Mobilization of local, regional, and systemic defenses

23. Figure 22.10 Nonspecific Defenses(Part 6 - Inflammatory Response) Figure 22.10

24. Figure 22.13 Inflammation Figure 22.13

25. Nonspecific Defenses, Fever • Maintenance of a body temperature above 37.2oC (99oF) • Pyrogens reset the hypothalamic thermostat and raise body temperature • Pathogens, toxins, antigen-antibody complexes can act as pyrogens

26. Figure 22.10 Nonspecific Defenses(Part 7 - Fever) Figure 22.10