The Lymphatic System and Body Defenses

Lymphatic System & Body Defenses Objective 1 Describe the structure and function of the structures composing the lymphatic system. Objective 2 Describe the composition of lymph, and explain its formation and transport

The Lymphatic System Lymphatic system functions Transport fluids back to the blood House the cells/chemicals involved with immunity

Lymph Lymph –fluid that leaks from other cells/blood. Carried by lymphatic vessels Properties of lymphatic system One way system toward the heart No pump

Lymphatic Vessels Lymph capillaries collect fluid from around blood vessels Figure 12.2

Lymph Materials returned to the blood Water Red/White Blood cells Proteins

Lymph Harmful materials that can enter lymph vessels Bacteria Viruses Cancer cells Cell debris

Lymph Nodes offer protection Filter lymph before it is returned to the blood Defense cells within lymph nodes Macrophages – engulf and destroy foreign substances Lymphocytes – provide immune response to antigens

Lymph Nodes Figure 12.3

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

The Spleen Located on the left side of the abdomen Filters blood Destroys worn out blood cells Acts as a blood reservoir

The Thymus Located low in the throat, overlying the heart Produces hormones (like thymosin) to program lymphocytes during childhood

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

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

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

Body Defenses Nonspecific defense system protect against a variety of invaders Responds immediately Specific defense system Specific defense is required for each type of invader Also known as the immune system

Body Defenses Figure 12.6

Lymphatic System & Body Defenses Objective 3 Describe the protective functions of skin and mucous membranes

Surface Membrane Barriers – First 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

Surface Membrane Barriers – First Line of Defense Stomach mucosa Secretes hydrochloric acid Has protein-digesting enzymes Saliva and lacrimal fluid (tears) contain lysozyme Mucus traps microogranisms in digestive and respiratory pathways

Lymphatic System & Body Defenses Objective 4 Explain the importance of phagocytes and natural killer cells

Defensive Cells – 2nd Line of Defense Phagocytes (neutrophils and macrophages) Engulfs foreign material into a vacuole Enzymes from lysosomes digest the material Figure 12.7a

Events of Phagocytosis Figure 12.7b

Defensive Cells Natural killer cells (yes…that is really their name…) Can lyse and kill cancer cells Can destroy virus- infected cells

Lymphatic System & Body Defenses Objective 5 Describe the inflammatory process

Inflammatory Response - Second Line of Defense Triggered when body tissues are injured Produces four cardinal signs Redness Heat Swelling Pain chain of events leads to protection and healing Prevents spread of damaging agents Disposes of cell debris and pathogens Sets the stage for repair

Steps in the Inflammatory Response Figure 12.8

Lymphatic System & Body Defenses Objective 6 Name antimicrobial substances produced in the body

Antimicrobial Chemicals Complement A group of at least 20 plasma proteins Activated when they encounter and attach to cells (complement fixation) Damage foreign cell surfaces Figure 12.10

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

Pyrogens Cause abnormally high body temperature = Fever Resets hypothalmus’ heat regulation system 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

Specific Defense: The Immune System – Third Line of Defense Antigen specific – recognizes and acts against particular foreign substances Systemic – not restricted to the initial infection site Has memory – recognizes and mounts a stronger attack on previously encountered pathogens

Lymphatic System & Body Defenses Objective 7 Define antigen and hapten, and name substances that act as complete antigens

Antigens (Nonself) Any substance capable of exciting the immune system and provoking an immune response Examples of common antigens Foreign proteins Pollen grains Microorganisms

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

Activation of Lymphocytes Figure 12.11

Lymphatic System & Body Defenses Objective 8 Name the two arms of the immune response and relate each to a specific lymphocyte type.

Types of Immunity Humoral immunity Cells produce chemicals for defense Antibody immunity Cellular immunity Cell-mediated immunity Cells target virus infected cells

Humoral (Antibody-Mediated) Immune Response B lymphocytes with specific receptors bind to a specific antigen The binding event activates the lymphocyte to undergo clonal selection A large number of clones are produced (primary humoral response)

Humoral (Antibody Mediated) Immune Response Most B cells become plasma cells Produce antibodies to destroy antigens Activity lasts for four or five days Some B cells become long-lived memory cells (secondary humoral response)

Humoral Immune Response Figure 12.12

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

Lymphatic System & Body Defenses Objective 11 List the 5 antibody classes and describe their specific roles

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

Antibody Structure Four amino acid chains 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

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

Antibody Function Antibodies inactivate antigens in a number of ways Complement fixation – lyse cell (bacteria) Neutralization – block/mask harmful effects (viruses) Agglutination – clump together Precipitation – settle out of solution, easier for body to break it down

Antibody Function Figure 12.16

Back to Cell Mediated Immunity…

Cells of the Immune System Lymphocytes Originate from the red bone marrow B lymphocytes become immunocompetent in the bone marrow T lymphocytes become immunocompetent in the thymus Macrophages Arise from monocytes Become widely distributed in lymph organs

Cellular (Cell-Mediated) Immune Response Antigens must be presented by macrophages to an activated T cell (antigen presentation) T cells must recognize nonself and self (double recognition) After antigen binding, clones form as with B cells, but different classes of cells are produced

Cellular (Cell-Mediated) Immune Response Figure 12.17

T Cell Clone Classes 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

T Cell Clones Suppressor T cells Release chemicals to stop the activity of T and B cells Stop the immune response to prevent uncontrolled activity A few members of each clone are memory cells

Summary of the Immune Response Figure 12.19

Organ Transplants and Rejection Major types of grafts Autografts – tissue transplanted from one site to another on the same person - “skin graft” Isografts – tissue grafts from an identical person (identical twin) – hence very rare Allografts – tissue taken from an unrelated person (most connon) Xenografts – tissue taken from a different animal species (pig heart valves)

Organ Transplants and Rejection Autografts and isografts are ideal donors Xenografts are never successful for long Allografts are more successful with a closer tissue match

Lymphatic System & Body Defenses Objective 12 Distinguish between active and passive immunity

Active Immunity Your B cells encounter antigens and produce antibodies Active immunity can be natural (from an infection) or artificial (vaccine/dead pathogen) acquired Figure 12.14

Passive Immunity Antibodies are obtained from someone else Conferred naturally from a mother to her fetus Conferred artificially from immune serum or gamma globulin Immunological memory does not occur Protection provided by “borrowed antibodies”

Lymphatic System & Body Defenses Objective 13 Distinguish between types of immunodeficiencies, allergies, and autoimmune diseases.

Disorders of Immunity: Allergies (Hypersensitivity) Abnormal, vigorous immune responses Types of allergies 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

Disorders of Immunity: Allergies (Hypersensitivity) Types of allergies (continued) Delayed hypersensitivity Triggered by the release of lymphokines from activated helper T cells Symptoms usually appear 1–3 days after contact with antigen

Allergy Mechanisms Figure 12.20

Disorders of Immunity: Immunodeficiencies Production or function of immune cells or complement is abnormal May be congenital (at birth) or acquired Includes AIDS – Acquired Immune Deficiency Syndrome

Disorders of Immunity: 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

Disorders of Immunity: Autoimmune Diseases Examples of autoimmune diseases Multiple sclerosis – white matter of brain and spinal cord are destroyed Myasthenia gravis – impairs communication between nerves and skeletal muscles Juvenile diabetes – destroys pancreatic beta cells that produce insulin Rheumatoid arthritis – destroys joints