1. The Lymphatic System Lymphatic system functions
Transport fluids from body tissues back to bloodstream
Play essential roles in body defense and resistance to disease
Consists of two semi-independent parts:
Lymphatic vessels
Lymphoid tissues and organs

2. Lymphatic Characteristics
Lymph – excess tissue fluid carried by lymphatic vessels
Pale white fluid, similar composition to blood plasma, but with more leukocytes, lymphocytes, and triglycerides

3. Lymphatic Vessels Lymphatic vessels
Carry lymph towards the heart, never away
No pump, moved by “milking” action of muscles

4. Lymphatic Vessels Lymphatic vessels
Fluid leaks into lymphatic capillaries from body tissue
Lymphatic collecting vessels collect it from lymph capillaries
Carries lymph to and away from lymph nodes
Figure 12.1

5. Lymphatic Vessels
Figure 12.2

6. Lymphatic Vessels Lymphatic collecting vessels (continued)
Returns fluid to circulatory veins near the heart
Figure 12.1

7. Lymph
As lymph seeps into lymph capillaries, harmful materials are carried with it:
Bacteria
Viruses
Cancer cells
Cell debris

8. Lymph Nodes
Lymph nodes filter lymph before it is returned to the blood

9. Lymph Nodes Leukocyte defense cells within lymph nodes:
Macrophages – engulf and destroy foreign substances
Lymphocytes – provide immune response to antigens

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

11. The Spleen Spleen: Filters out and destroys worn out blood cells
Acts as a blood reservoir
Synthesizes antibodies, filters antibody-coated cells from blood

12. The Thymus
Thymus:
Produces hormones (like thymosin) to program (“educate”) certain lymphocytes

13. Tonsils Tonsils: Small masses of lymphoid tissue around the pharynx
Trap and remove bacteria and other foreign materials

14. Peyer’s Patches Peyer’s Patches:
Found in the wall of the small intestine
Capture and destroy bacteria in the intestine

15. Body Defenses
The body is constantly in contact with bacteria, fungi, and viruses
The body has two defense systems for foreign materials: nonspecific and specific

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

17. Body Defenses
Figure 12.6

18. Nonspecific Body Defenses
First Line of Defense:
Body surface coverings and their secretions
Intact skin - physical barrier, acidic pH
Mucous membranes - mucus, protein-digesting enzymes, HCl (in stomach)

19. Nonspecific Body Defenses
Second Line of Defense:
Non-specific defense cells
Phagocytes (like macrophages) - engulf & digest foreign matter
Natural killer (NK) cells - lyse & destroy cancerous or virus-infected cells
Antimicrobial chemicals
The inflammatory response
Fever

20. Antimicrobial Chemicals
Two kinds: Complement, Interferon
Complement
Plasma proteins
Lyse microorganism, enhance phagocytosis
Figure 12.10

21. Antimicrobial Chemicals
Interferon
Secreted proteins of virus-infected cells
Bind to healthy cell surfaces to inhibit viruses binding

22. Inflammatory Response
Inflammation: an increase in blood flow, tissue fluid, and clotting proteins in a specific area
Prevents spread of foreign agents to neighboring tissues, disposes of pathogens & debris, promotes tissue repair, releases chemicals that attract immune cells
Triggered when body tissues are injured
Signs: redness, heat, swelling, pain

23. Steps in the Inflammatory Response
Figure 12.8

24. Fever Abnormally high body temperature
Hinders pathogens with temperature preferences
Increases mobility of leukocytes, rate of phagocytosis, production rate of certain lymphocytes