1. Chapter 12 The Lymphatic System and Body Defenses

2. The Lymphatic System Consists of two semi-independent parts  Lymphatic vessels  Lymphoid tissues and organs Lymphatic system functions  Transport fluids back to the blood  Play essential roles in body defense and resistance to disease

4. Lymphatic Characteristics Interstitial Fluid – Fluid that has leaked out of the capillaries and surrounds body cells. Lymph – excess tissue fluid carried by lymphatic vessels.

5. Properties of lymphatic vessels  One way system toward the heart  No pump  Lymph moves toward the heart - Milking action of skeletal muscle - contraction of sm. muscle in vessels

6. Lymph Capillaries  Walls overlap - flap-like minivalves  Fluid leaks into lymph capillaries  Capillaries anchored by filaments  Higher press on inside closes minivalves

8. Lymphatic Collecting Vessels  Collects lymph from lymph capillaries  Carries lymph to and away from lymph nodes Figure 12.2  Returns fluid to circulatory veins near the heart -Right lymphatic duct -Thoracic duct

11. Lymph Materials returned to the blood water blood cells proteins Harmful materials that enter lymph vessels  Bacteria  Viruses  Cancer cells  Cell debris

12. Lymph Node Structure  Most are kidney-shaped, less than 1 inch long  Cortex -Outer part -Contains follicles – collections of lymphocytes  Medulla -Inner part -Contains phagocytic macrophages

13. Lymph Nodes  Filters out bacteria, soot, and cancer cells before lymph is returned to the blood  Defense cells within lymph nodes  Macrophages – engulf and destroy foreign substances  Lymphocytes – provide immune response to antigens

14. Flow of Lymph Through Nodes  Lymph enters the convex side through afferent lymphatic vessels  Lymph flows through a number of sinuses inside the node  Lymph exits through efferent lymphatic vessels  Fewer efferent than afferent vessels causes flow to be slowed

16. Other Lymphoid Organs Several other organs contribute to lymphatic function  Spleen  Thymus  Tonsils  Peyer’s patches Figure 12.5

17. The Spleen  Located on the left side of the abdomen  Largest lymphoid organ  Filters blood, not lymph  Destroys worn out blood cells  Forms blood cells in the fetus  Acts as a blood reservoir

18. Very rich blood supply so when injured may require a splenectomy.

19. The Thymus  Located low in the throat (mediastinum), overlying the heart  Functions at peak levels only during childhood  Lymphocytes develop under the influence of the hormone thymosin

21. Tonsils  Small masses of lymphoid tissue around the pharynx  Trap and remove bacteria and other foreign materials  Tonsillitis is caused by congestion with bacteria

23. Peyer’s Patches  Found in the wall of the small intestine  Resemble tonsils in structure  Capture and destroy bacteria in the intestine

24. Mucosa-Associated Lymphatic Tissue (MALT) Includes:  Peyer’s patches  Tonsils  Other small accumulations of lymphoid tissue  Acts as a sentinal to protect respiratory and digestive tracts

25. Body Defenses The body is constantly in contact with bacteria, fungi, and viruses The body has two defense systems for foreign materials Nonspecific defense system Specific defense system

26. Body Defenses A. Nonspecific defense system  Mechanisms protect against a variety of invaders  Responds immediately to protect body from foreign materials B. Specific defense system  Specific defense is required for each type of invader  Also known as the immune system

27. Nonspecific Body Defenses

28. Surface Membranes – 1st Line of Defense The skin - Physical barrier to foreign materials  pH acidic to inhibit bacterial growth  Sebum is toxic to bacteria Stomach mucosa:  Secretes hydrochloric acid  Has protein-digesting enzymes Body Openings/Secretions:  Saliva and lacrimal fluid contain lysozyme  Vaginal secretions are very acidic  Mucus traps microogranisms

29. Internal Defenses (2 nd Line) – Cells and Chemicals  Natural killer cells - Unique lymphocytes - Can lyse and kill cancer cells -Can destroy virus-infected cells -They detect foreign cells by their lack of certain self surface molecules. -Do not phagocytize, but rather release a lytic chemical called perforins that disintegrates the cell membrane.

30. Internal Defenses – Cells and Chemicals  Phagocytes - neutrophils & macrophages - Engulfs foreign material into a vacuole - Enzymes from lysosomes digest the material

31. Inflammatory Response - 2 nd Line of Defense  Triggered when body tissues are injured - release histamine and kinins  Produces four cardinal signs - Redness - Heat - Swelling -Pain  Results in a chain of events leading to protection and healing

33. Causes blood vessels to dilate…

34. … and become leaky. Margination

35. Chemotaxis and Diapedesis

38. Functions of the Inflammatory Response  Prevents spread of damaging agents  Disposes of cell debris and pathogens  Sets the stage for repair

39. Antimicrobial Chemicals – 2 nd Line Complement  A group of at least 20 plasma proteins  Activated when they encounter and attach to cells (complement fixation)  Damage foreign cell surfaces

40. Membrane attack complexes (MAC) causes wholes in cell Membrane and the cell will burst. Complement can also increase the inflammatory response, cause vasodilation, and chemotaxis. Can also result in opsonization, causing the cell membranes of foreign cells to become sticky making it easier for them to be phagocytized.

41. Antimicrobial Chemicals – 2 nd Line Interferon  Secreted proteins of virus-infected cells  Bind to healthy cell surfaces to inhibit viruses binding

42. Fever – 2 nd Line  Abnormally high body temperature  Hypothalamus heat regulation can be reset by pyrogens (secreted by white blood cells)  High temperatures inhibit the release of iron and zinc from liver and spleen needed by bacteria  Fever also increases the speed of tissue repair