1. Lymphatic System and Body Defenses Chapter 12

2. The Lymphatic System Two semi-independent parts ◦ Lymphatic vessels ◦ Lymphoid tissues and organs Function of lymphatic system ◦ Transport fluids back to the blood ◦ Essential role in body defense and disease resistance

3. Lymphatic Vessels Function – Pick up excess tissue fluid – Lymph – and return it to the blood stream Also known as lymphatics One way system flows only to the heart Characteristics – Thin-walled – Valved – pumpless

4. Lymph capillaries Web between tissue cells and blood capillaries Remarkably permeable Held by fine collagen fibres Act as one way doors ◦ Flap like mini valves close as high pressure builds up inside ◦ Keeps lymph from leaking back

5. Lymphatic collecting vessels Collects lymph from lymph capillaries Carries lymph to and away from lymph node Returns fluid to the heart through two ducts ◦ Right lymphatic duct  Drains lymph from right arm and right side of head and thorax ◦ Thoracic duct  Receives lymph from rest of the body

6. Lymphatic Vessels

7. Lymph Nodes Function – Remove foreign material from lymph Cluster along vessels in three main areas – Inguinal – Axillary – Cervical Contain 2 types of cells – Macrophages Engulf and destroy bacteria, viruses and foreign substances – Lymphocytes (white blood cells) Respond to foreign substances

8. Lymph Nodes (continued) Structure – Kidney shaped, less than 1” long – “buried” in connective tissue – Cortex Outer part Contains follicles (collections of lymphocytes) and T-cells – Medulla Inner part Contains phagocytic macrophages

9. Flow of Lymph through Nodes Lymph enters through afferent lymph vessels Flows through sinuses Exits at indented region - hilus – through efferent lymphatic vessels Slow process ◦ Allows time for lymphocytes and macrophages to perform

11. Other Lymphoid Organs Spleen Thymus Tonsils Peyer’s patch Common features ◦ Predominance of reticular connective tissues and lymphocytes

12. Other Lymphoid Organs Spleen ◦ Filters blood of bacteria, viruses ◦ Located on left side of abdominal cavity ◦ Destroys worn out red blood cells ◦ Acts as blood reservoire ◦ Produces lymphocytes Thymus ◦ Function peaks at youth ◦ Found low in throat over heart ◦ Produces hormones that program lymphocytes

13. Other Lymphoid Organs Tonsils ◦ Small masses of lymphatic tissue around pharynx ◦ Trap and removes bacteria or pathogens entering throat ◦ So efficient can become congested  tonsillitis Peyer’s patches ◦ Like tonsils but in small intestine ◦ Captures and destroys bacteria

14. Mucosa-associated Lymphatic Tissue (MALT) Composed of ◦ Peyer’s patches ◦ Tonsils ◦ Other small collections of lymphatic tissue Protects respiratory and digestive tracts

16. Body Defenses Two systems to fight off bacteria, viruses and fungi that your body comes in contact with ◦ Nonspecific body defenses  Responds immediately to all foreign substances  Provided by intact skin and mucous membranes, the inflammatory response and proteins ◦ Specific body defenses  The Immune System  Responds to particular foreign substances

17. Nonspecific Body Defenses Some nonspecific resistance is inherited Refers to mechanical barriers that cover body surfaces and specialized cells Lines of defense ◦ Surface Membrane Barriers ◦ Cells and Chemicals

18. Surface Membrane Barriers First line of defense The Skin- ◦ As long as unbroken, strong physical barrier Mucous membranes provide similar responses Both produce variety of chemicals ◦ Acid pH of skin prevents bacterial growth ◦ Stomach mucosa secretes hydrochloric acid and enzymes that kill pathogens ◦ Saliva and lacrimal fluid contain lysozume ◦ Mucus traps microorganisms that enter digestive and respiratory pathways.

19. Surface Membrane Barriers continued Structural modifications fend off potential invaders When surface barriers broken, infection occurs ◦ Microorganisms invade deeper tissues and other mechanisms come into play

20. Cells and Chemicals Second line of defense Rely on ◦ phagocytes and natural killer cells ◦ Inflammatory response ◦ Chemical substances Fever also a nonspecific protective response

21. Phagocytes Located in nearly every body organ Engulf foreign particles, like amoebas Binds to particle then pulls it in Enclosed in vacuole Fused with enzymatic contents of lysosome Contents broken down or digested

22. Events of Phagocytosis

23. Natural Killer Cells “police” body in blood and lymph Can lyse and kill cancer and virus-infected body cells Act against any target by recognizing sugars on intruder’s surface

24. Inflammatory Response Occurs whenever body tissues injured Four cardinal signs ◦ Redness ◦ Heat ◦ Swelling ◦ Pain Chain of events leading to protection and healing

25. Inflammatory Response continued What does it do? ◦ Prevents spread of damaged agents to nearby tissues ◦ Disposes of cell debris and pathogens ◦ Sets stage for repair Other protected events are clotting Heat increases defensive actions and repair processes

26. Third Line of Defense Immune response mediated by lymphocytes ◦ Respond to pathogens that have previously invaded the body

27. The Inflammatory Response

28. Antimicrobial Chemicals Two types ◦ Complement proteins  Group of 20 plasma proteins  Circulate in blood in inactive state  Activated when fixed to pathogen  Damage foreign cell surfaces  Release vasodilators, chemotaxis chemicals and cause opsonixation ◦ Interferon  Bind to near by cells when viruses are present  Hinders ability of viruses to multiply within cells

29. Fever Abnormally high body temperature Response to invading microorganisms Body thermostat can be reset in response to pyrogens High fevers are dangerous Mild/moderate fevers benefit the body ◦ Speeds up repair processes Liver and spleen gather iron and zinc during fevers preventing bacteria from multiplying

30. Specific Body Defenses: The Immune System