The Lymphatic System and Body Defenses

1. 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 • Body defense and resistance to disease

3. Lymphatic Characteristics • Lymph – excess tissue fluid carried by lymphatic vessels • Properties of lymphatic vessels • One way system toward the heart • No pump • Lymph moves toward the heart • Milking action of skeletal muscle • Rhythmic contraction of smooth muscle in vessel walls

4. Lymphatic Vessels • Lymph Capillaries • Walls overlap to form flap-like minivalves • Fluid leaks into lymph capillaries • Capillaries are anchored to connective tissue by filaments • Higher pressure on the inside closes minivalves

5. Lymphatic Vessels

6. Lymphatic Vessels • Lymphatic collecting vessels • Collects lymph from lymph capillaries • Carries lymph to and away from lymph nodes • Returns fluid to circulatory veins near the heart at the right lymphatic duct or thoracic duct

7. Lymph • Lymph returned to the blood is composed of: • Water • Blood cells • Proteins • Harmful materials that enter lymph vessels • Bacteria • Viruses • Cancer cells • Cell debris

8. Lymph Nodes • Filter lymph before returning to the blood • Contain defense cells: • Macrophages – engulf and destroy foreign substances • Lymphocytes – provide immune response to antigens

9. Lymph Nodes

10. Most are kidney-shaped, <1 inch long Cortex - outer part Contains follicles with lymphocytes Medulla - Inner part Contains phagocytic macrophages Lymph Node Structure

11. The 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

12. Other Lymphoid Organs • Several other organs contribute to lymphatic function: • Spleen • Thymus • Tonsils • Peyer’s patches

13. The Spleen • Located on the left side of the abdomen • Filters blood – cleanses blood of bacteria, viruses and debris • Destroys worn out blood cells • Stores platelets • Acts as a blood reservoir • Forms blood cells in the fetus (hematopoietic) • Produces lymphocytes only in the adut spleen

14. The Thymus • Located low in the throat, overlying the heart • Functions at peak levels only during childhood • Produces hormones (like thymosin) to program lymphocytes

15. Tonsils • Small masses of lymphoid tissue around the pharynx • Traps and removes bacteria and other foreign materials • Tonsillitis = is caused by congestion with bacteria

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

17. 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 from foreign matter

18. 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

19. Body Defenses • Nonspecific defense system • Mechanisms protect against a variety of invaders • Responds immediately to protect body from foreign materials • Provided by body surface coverings • intact skin, mucous membrane, cellular proteins and inflammatory response. • Specialized human cells • Chemicals produced by the body • Specific defense system • Known as the immune system • Specific defense is required for each type of invader

20. Body Defenses Figure 12.6

21. Surface Membrane Barriers1st Line of Defense • The skin • Physical barrier to foreign materials • pH of the skin is acidic to inhibit bacterial growth • Sebum is toxic to bacteria • Vaginal secretions are very acidic • Stomach mucosa • Secretes hydrochloric acid • Has protein-digesting enzymes • Saliva and lacrimal fluid contain lysozyme • Mucus traps microogranisms in digestive and respiratory pathways

22. Defensive Cells • Phagocytes (neutrophils and macrophages) • Engulfs foreign material into a vacuole • Enzymes from lysosomes digest the material • Natural killer cells • Can lyse and kill cancer cells • Can destroy virus- infected cells Figure 12.7a

23. Events of Phagocytosis

24. Inflammatory Response – 2nd Line of Defense • Triggered when body tissues are injured • Produces four cardinal signs • Redness • Heat • Swelling • Pain • Results in a chain of events leading to protection and healing Inflammatory Response

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

26. The Inflammatory Response • Begins with a chemical ‘alarm”- Histamines when cells are injured • Blood vessels dilate increases blood flow to area causing redness and heat. • Capillary beds become permeable becoming leaky, which increases edema • Pain receptors are activated • Phagocytes and WBC are attracted to the area: • Chemotaxis = cells follow chemical gradient

27. Antimicrobial Chemicals • Complement proteins • 20 active plasma proteins circulating in the blood • Attach to foreign cells and fight against them. • Interferon • Secreted proteins of virus-infected cells • Bind to healthy cell surfaces to inhibit viruses binding

28. Fever • Abnormally high body temperature • Systemic response to invading microorganisms • Heat regulated by Hypothalmus ‘thermostate’ - reset upwards 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

29. Specific Defense: The Immune System3rd Line of Defense • Antigen specific – recognizes and acts against particular foreign substances • It stalks and eliminates any invading pathogen • Systemic – not restricted to the initial infection site • Has memory – recognizes and mounts a stronger attack on previously encountered pathogens

30. 2 Types of Immunity • Humoral immunity • Its Antibody-mediated immunity where antibodies are present in the body’s fluids • Cells produce chemicals for defense • Cellular immunity • Cell-mediated immunity where lymphocytes themselves defend the body. • Cells are the protective factors that target virus infected cells

31. Antigens (Nonself = foreign intruders) • Antigen = any substance capable of exciting the immune system and provoking an immune response • Examples of common antigens: • foreign proteins, nucleic acids, large carbohydrates, pollen grains, microorganisms • As the immunity system develops, it inventories all these proteins so it recognizes them as self.

32. Self-Antigens • Human cells have many surface proteins • Our immune cells do not attack our own proteins • Our cells in another person’s body can trigger an immune response because they are foreign • Restricts donors for transplants

33. Allergies • Many small molecules (called haptens or incomplete antigens) are not antigenic, but link up with our own proteins • The immune system may recognize and respond to a protein-hapten combination • The immune response is harmful rather than protective because it attacks our own cells • Haptens are found in chemicals, poison ivy, animal dander, detergens, hair dyes, cosmetics, housefold/industrial products.

34. Crucial Cells of the Immune System • 2 types of Lymphocytes • B lymphocytes (B cells) become immunocompetent in the bone marrow; produce antibodies, oversee humoral immunity. • T lymphocytes (T cells) become immunocompetent in the thymus; • Originate from hemocytoblasts in the red bone marrow • Macrophages • Arise from monocytes • Become widely distributed in lymphoid organs • Do not respond to specific antigens but help lymphocytes do that

35. Activation of Lymphocytes

36. Secondary Response • Memory cells are long-lived • A second exposure causes a rapid response • The secondary response is stronger and longer lasting Figure 12.13

37. Active Immunity • Your B cells encounter antigens and produce antibodies • Active immunity can be naturally or artificially acquired (vaccines Figure 12.14

38. Passive Immunity • Antibodies are obtained from someone else • From a mother to her fetus • Artificially from immune serum or gamma globulin • Immunological memory does not occur • Protection provided by “borrowed antibodies” is short-lived

39. Monoclonal Antibodies • Antibodies prepared for clinical testing or diagnostic services • Produced from descendents of a single cell line and exhibit specificity for only one antigen. • Examples of uses for monoclonal antibodies • Diagnosis of pregnancy • Treatment after exposure to hepatitis and rabies

40. Antibodies (Immunoglobulins) (Igs) • Soluble proteins secreted by B cells (plasma cells) • Carried in blood plasma • Capable of binding specifically to an antigen Figure 12.15a

41. Antibody Structure • Four amino acid chains linked by disulfide bonds • Two identical amino acid chains are linked to form a heavy chain • The other two identical chains are light chains • Specific antigen-binding sites are present Figure 12.15b

42. Antibody Classes • Antibodies of each class have slightly different roles • Five major immunoglobulin classes • IgM – can fix complement • IgA – found mainly in mucus • IgD – important in activation of B cell • IgG – can cross the placental barrier • IgE – involved in allergies

43. T Cell Clones • Cytotoxic T cells • Specialize in killing infected cells • Insert a toxic chemical (perforin) • Helper T cells • Recruit other cells to fight the invaders • Interact directly with B cells • Suppressor T cells • Release chemicals to suppress the activity of T and B cells • Stop the immune response to prevent uncontrolled activity • A few members of each clone are memory cells

44. Organ Transplants and Rejection • Major types of grafts • Autografts – tissue transplanted from one site to another on the same person • Isografts – tissue grafts from an identical person (identical twin) • Allografts – tissue taken from an unrelated person • Xenografts – tissue taken from a different animal species (Bovine)

45. Organ Transplants and Rejection • Autografts and isografts are ideal donors • Xenografts are never successful • Allografts are more successful with a closer tissue match

46. Disorders of the Immunity • Allergies (Hypersensitivity) • Immunodeficiencies • Autoimmune Diseases

47. Disorders of Immunity: Allergies (Hypersensitivity) • Abnormal, vigorous immune responses • (2) Types of allergies: 1)- Immediate hypersensitivity • Triggered by release of histamine from IgE binding to mast cells • Reactions begin within seconds of contact with allergen • Anaphylactic shock – dangerous, systemic response

48. Disorders of Immunity: Allergies (Hypersensitivity) 2) Delayed hypersensitivity • Triggered by release of lymphokines from activated helper T cells • Symptoms usually appear 1–3 days after contact with antigen Example: Contact dermititis

49. Disorders of Immunity: Immunodeficiencies • Production or function of immune cells or complement is abnormal • May be congenital or acquired • Includes AIDS – Acquired Immune Deficiency Syndrome SCID – Severe combined immunodeficiency disease (bubble babies)

50. Autoimmune Diseases • The immune system does not distinguish between self and nonself • The body produces antibodies and sensitized T lymphocytes that attack its own tissues • Multiple sclerosis – myelin sheath of brain & spinal cord are destroyed • Myasthenia gravis – impairs communication between nerves & skeletal muscles • Glomerulonephritis – impairment of renal function • Type I diabetes – destroys pancreatic beta cells that produce insulin • Rheumatoid arthritis – destroys joints • Systemic lupus erythematosus – affects kidney, heart, lung & skin