Lymphatic System and Body Defenses

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

15. Body Defenses

16. Nonspecific Body Defenses

17. Specific Body Defenses: The Immune System