Lymphatic System and Body Defenses

1. Lymphatic System and Body Defenses Unit 11

2. Lymphatic System • Defense against disease • Consists of two semi-independent parts: • Network of lymphatic vessels • Various lymphoid tissues and organs throughout body • Lymphatic vessels transport fluids that have escaped from the blood vascular system back to the blood. • Lymphoid organs house phagocytic cells and lymphocytes

3. Lymphatic Vessels • Fluid is forced out of the blood in the capillary beds, and most of it is reabsorbed at the venous ends. • About 3 L per day are left behind  this becomes part of the interstitial fluid, and is now called lymph. • This fluid must return to the bloodstream in order to have enough volume for the cardiovascular system to function • If this does not happen, fluid starts to build up in the tissues, producing edema (swelling)

4. Lymphatic Vessels • One way system  vessels only flow towards the heart • Low-pressure and pumpless system • Lymph capillaries = microscopic, blind ended vessels that spread out between tissues cells and blood capillaries in the loose connective tissues of the body. • Little valves at the end  open when fluid pressure is higher in the interstitial space, but close up when the pressure is higher inside the lymphatic vessels  prevents leaks

5. Lymphatic Vessels • Large particles like proteins, cell debris, bacteria, and viruses can’t enter blood capillaries, but they can enter lymphatic capillaries, especially in inflamed areas • Now the bacteria and viruses can travel throughout the body  how do we solve that problem? • Lymph takes “detours” through lymph nodes  gets cleaned of debris and “examined” by cells in the immune system

6. Lymphatic Vessels • Lymph moves from lymph capillaries to successively larger lymphatic vessels (lymphatic collecting vessels), similar to how blood moves from capillaries to venules to veins. • Lymph returns to venous system through one of two large ducts: • Right lymphatic duct – drains lymph from right arm and right side of head and thorax • Thoracic duct – receives lymph from the rest of the body • Both ducts empty into subclavian veins • Lymphatic vessels are thin walled and the larger ones have valves to prevent backflow, like veins. • Also helped by skeletal muscles “milking” the lymph along and pressure change in the thorax during breathing.

7. Lymph Nodes • Help protect the body by removing foreign material such as bacteria and tumor cells from the lymphatic stream as well as producing lymphocytes. • Lymph nodes = filters • Large clusters can be found in the inguinal (hips), axillary (armpits), and cervical (neck) regions of body. • Contain macrophages, which engulf and destroy bacteria, viruses, and other foreign substances found in lymph • Also contain lymphocytes, a type of WBC • Active infection usually results in swollen glands due to the trapping function of the nodes.

8. Lymph Nodes • Usually kidney-shaped, less than 1 inch long, and “buried” in connective tissue that surrounds them. • Each node is surrounded by a fibrous capsule • Trabeculae= strands that extend into the capsule to divide them into compartments • Cortex = outer part of the node, contains collections of lymphocytes called follicles • Germinal centers = dark centers of follicles that enlarge when B lymphocytes generate plasma cells • Medulla = center of lymph node, contains phagocytic macrophages • Lymph enters through afferent lymphatic vessels, moves through sinuses, and exits through efferent lymphatic vessels.

9. Lymph Nodes

10. Spleen • Blood rich organ that filters blood • Located on the left side of abdominal cavity, curls around stomach • Doesn’t filter lymph, it filters blood and cleans out bacteria, viruses, and other debris • Destroys worn out RBCs and returns their breakdown products to the liver • Stores platelets and acts as a blood reservoir (like the liver) • During hemorrhage, the spleen will contract and empty its stored blood back into circulation to help keep levels normal • Forms all blood cells in a fetus, but only lymphocytes are made in adults

11. Thymus • Lymphatic mass found low in throat overlying the heart • Produces hormones (thymosin and others) that function in the programming of certain lymphocytes so that they can protect the body • Functions at peak levels only during youth

12. Tonsils • Small masses of lymphatic tissue that ring the pharynx (throat) • Trap and remove any bacteria or other foreign pathogens entering the throat • Sometimes they work too well  get congested with bacteria and become red, swollen, and sore = tonsillitis

13. Peyer’s Patches • Resemble tonsils, but found in wall of small intestine • Macrophages in ideal position to capture and destroy bacteria  lots of bacteria in intestine • Help stop bacteria from penetrating intestinal wall • Peyer’s patches and tonsils are known as mucosa-associated lymphatic tissue (MALT) • MALT protects upper respiratory and digestive tracts  never-ending attacks of foreign matter

14. Lymphoid Organs

15. Body Defenses • Two main systems: • Nonspecific – responds immediately to protect body from all foreign substances, reduces workload of specific defense system • Intact skin and mucous membranes • Inflammatory response • Specific – aka immune system, attacks particular foreign substances • Lymphatic organs • Blood vessels • White blood cells

16. Surface Membrane Barriers • First line of defense = skin and mucous membranes • Act as physical barriers • Acid pH of skin inhibits bacterial growth • Stomach mucosa makes hydrochloric acid and protein-digesting enzymes, which helps kill pathogens • Saliva and tears contain lysozyme, an enzyme that destroys bacteria • Sticky mucus traps microorganisms in digestive and respiratory pathways

17. Cells and Chemicals • Second line of defense • Phagocytes – engulfs a foreign particle and digests it • Natural killer (NK) cells – lyse and kill cancer cells and virus-infected cells  can react against any target. They attack the cell’s membrane and release chemicals that cause it to disintegrate • Fever – abnormally high body temperature, pyrogens are chemicals secreted by WBCs that raise body temperature, fevers can be very dangerous if they get too hot or last too long • Inflammatory response – triggered when body tissues are injured  4 cardinal signs = redness, heat, swelling, and pain.

18. Inflammatory Response • Injured cells release histamine and kinins • Cause blood vessels to dilate and capillaries to become “leaky”  increased blood flow • Activate pain receptors • Attract phagocytes and WBCs to area  chemotaxis = cells following chemical gradient • Swelling (edema) is the result  causes more pain • The inflammatory response prevents the spread of damaging agents, disposes of cell debris and pathogens, and sets the stage for repair

19. Recap • Lymphatic system defends against disease • Lymphatic vessels • Various lymphatic tissues and organs • Lymph • One way system  towards the heart • 1st line of defense = skin and mucus membranes • 2nd line of defense = cells, chemicals, and inflammatory response

20. Immune System • Third line of defense • Immune response – immune system’s response to a threat; increases inflammatory response and provides protection against specific antigens • Recognizes foreign molecules (antigens) and actively works to destroy them • Can recognize previously encountered antigens and trigger immune responses • Immunology – study of immunity • Some diseases that result from a malfunctioning immune system: cancer, rheumatoid arthritis, AIDS

21. Three important aspects of immune response: • 1. Antigen specific – recognizes and acts against particular pathogens or foreign substances • 2. Systemic – Immunity is not restricted to the initial infection site • 3. “Memory” – recognizes and mounts stronger attacks on previously encountered pathogens

22. Two kinds of immunity • 1. Antibody-mediated immunity (humoral immunity) = provided by antibodies present in body’s fluids. • 2. Cell-mediated immunity = Lymphocytes themselves defend the body, either by directly lysing foreign cells or indirectly releasing chemicals that enhance inflammatory response

23. Antigens • Any substance capable of exciting our immune system and provoking an immune response. • Tend to be large • Not normally present in our bodies • Foreign intruders  “non-self” • Our own cells have self-antigens, which are recognized by our body, but would trigger an immune response in someone else (organ transplant rejections)

24. Cells of the Immune System • Lymphocytes • B lymphocytes (B cells) – produce antibodies and oversee antibody-mediated immunity • T lymphocytes (T cells) – do not produce antibodies and oversee cell-mediated immunity • Lymphocytes must be able to recognize body’s own cells so they won’t attack them • Lymphocytes get “trained” to recognize one distinct antigen to attack = immunocompetent • Since lymphocytes become immunocompetent before being exposed to antigens, we know it is our genes, not antigens, that determine what foreign substances we will be able to resist.

25. Cells of the Immune System • Macrophages – “big eaters” • Engulf foreign particles and present fragments of these antigens on their own surfaces • Allow these particles to be recognized by immunocompetent T cells – antigen presenters • Macrophages secrete monokines, which activate T cells • Active T cells release chemicals that turn macrophages into killer macrophages

26. Antibody-Mediated Response • Primary humoral response = Immature B cell binds to antigen  gets activated and undergoes clonal selection (mass produces an army of cells like itself) • Afterwards, most clones become plasma • Some become long-lived memory cells and can respond to the antigen when they encounter it later = secondary response

27. Two kinds of Humoral Immunity • Active immunity = B cells encounter antigens and produce antibodies against them • Naturally acquired = bacterial and viral infections • Artificially acquired = vaccinations • Passive immunity = Antibodies received from immune human or animal donor  temporary protection that ends when “borrowed antibodies” naturally degrade in the body • Naturally acquired = mother’s antibodies cross over placenta to fetus • Artificially acquired = After receiving immune serum or gamma globulin (used for treating rabies, hepatitis, snake bites, botulism, tetanus, etc.)

28. Antibodies • Also referred to as immunoglobulins (Igs) • Soluble proteins secreted by activated B cells in response to an antigen  capable of binding specifically to that antigen • Basic structure – four amino acid (polypeptide) chains linked by disulfide bonds • 2 chains = Heavy chains, 2 chains = Light chains • Variable and constant regions

29. Antibodies • Five major classes – IgM, IgA, IgD, IgG, IgE • Remember – MADGE • Slightly different biological roles • Antibodies can function through: • Complement fixation = activated during nonspecific body defenses, antibodies attached to cellular targets cause the cell to lyse • Neutralization = antibodies bind to specific sites on bacteria or viruses, making them inactive • Agglutination = cross-linking between antibodies and antigens causes clumping • Precipitation = cross-linking makes clumps so big, they settle out of solution

30. Cell-Mediated Response • T cells are activated to form clones after binding with “recognized” antigen • Antigens must be “presented” by macrophages • Different types of T cells: • Helper T cells = interact directly with B cells bound to antigens. They liberate lymphokines, chemicals that enhance the killing activity of macrophages, attract other leukocytes, or act as helper factors. • Cytotoxic (killer) T cells = directly attack and lyse infected and cancerous cells. • Delayed hypersensitivity T cells = release chemicals that enhance inflammation and promote a delayed allergic reaction • Suppressor T cells = terminate normal immune response by releasing suppressor chemicals

31. Immunity Disorders • Allergy/hypersensitivity = overreaction to otherwise harmless antigen • Immunodeficiency = abnormalities in any immune element (AIDS) • Autoimmune disease = body’s self-tolerance breaks down, antibodies attack bodies own cells and tissues • http://www.youtube.com/watch?v=l-2ilZA-_aw&feature=related