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Lymphatic System and Disorders BIO 238 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Functions of the Lymphatic System ▫ Return excess interstitial fluid to the blood Helps maintain water balance in the body ▫ Involved in the absorption of fats from digestive tract through lacteals ▫ Works with white blood cells to protect the body against pathogens Lymph • Lymph is the fluid flowing inside lymphatic vessels ▫ Derived from blood plasma • Formation of lymph ▫ Capillary leakage causes blood proteins to enter interstitial fluid (IF); increases osmotic pressure ▫ Excess fluid accumulates in the interstitial space ▫ Lymphatic vessels pick up and return the accumulated fluid to blood ▫ This process prevents edema from occurring in body tissues Lymphatic Capillaries and Vessels • Lymphatic trunks drain into lymphatic collecting ducts ▫ Right lymphatic duct R side of head and neck , R arm and shoulder, R thorax ▫ Thoracic duct Remainder of body • Collecting ducts empty into the R or L subclavian veins Lymphatic Organs • All lymphatic organs are site of lymphocyte production • Lymphocytes may remain in the lymphatic organs or migrate in blood to other sites Lymph Nodes • Widely distributed throughout body • Filters and cleanses lymph ▫ Trapped substances are destroyed by lymphocytes and macrophages Tonsils ▫ Lymphatic tissue underneath mucus membranes of nasal and oral cavities ▫ Intercept and destroy pathogens that enter through nose and mouth ▫ Three groups of tonsils Palatine tonsils Pharyngeal tonsil Lingual tonsils • Thymus ▫ Located in the mediastinum ▫ Large in infants and decreases in size with age ▫ Produces thymosin, which promotes T lymphocytes (T cells) differentiation and division Spleen ▫ Cleanses and filters blood and lymph ▫ Store reserve supply of red blood cells ▫ Major site of red blood cell destruction and removal ▫ Major site of lymphocyte production Nonspecific Resistance Against Disease • Protection against all pathogens and foreign substances Not directed against a specific pathogen • Mechanisms include ▫ ▫ ▫ ▫ ▫ Mechanical barriers Chemical actions Phagocytosis Inflammation Fever Mechanical and Chemical Barriers • Mechanical Barriers ▫ Skin Packed epidermal cells Acid pH ▫ Mucus membranes Trap foreign substances ▫ Tears ▫ Saliva ▫ Urine flow • Chemical Actions ▫ Lysozyme: destroys bacteria ▫ Mucus: traps pathogens ▫ Gastric juice: low pH and enzyme pepsin ▫ Interferon: causes uninfected cells to make antiviral replication proteins Phagocytosis ▫ The engulfing and destruction of microorganisms ▫ Carried out by neutrophils and monocytes Monocytes entering the infected tissues are called macrophages Inflammation ▫ Localized response to infection or injury Promotes pathogen destruction and the healing process ▫ Characterized by redness, pain, heat, and swelling ▫ Process of inflammation Cells release chemicals that dilate arterioles and increase capillary permeability Increased blood flow causes redness and heat Increased fluid movement out of capillaries causes swelling Irritations of nerve endings causes pain Pus Accumulated mass of living and dead leukocytes, tissue cells, and bacteria at the infection site Fibrinogen and fibroblasts work to seal off the infected area and prevent pathogen spread Dead pathogens are cleaned up by phagocytes New cells are formed to repair area of damage Fever ▫ Abnormally high body temperature ▫ Functions Inhibits growth of certain pathogens Increases rates of body processes, including those that fight infections Immunity • Specific resistance directed at specific pathogens and foreign cells ▫ Production of specific cells and substances that attack a specific invader • It has a “memory” ▫ Allows a quicker and stronger response to subsequent infections • Involves lymphocytes and macrophages ▫ Separated into cell-mediated immunity and antibody-mediated immunity Specialization of Lymphocytes ▫ Lymphocytes are born in red bone marrow ▫ Lymphocyte specialization In the thymus become T lymphocytes (T cells) In bone marrow, spleen, or liver become B lymphocytes (B cells) ▫ T and B cells flow through the blood to lymphatic organs where they form large populations ▫ 75% of circulating lymphocytes are T cells ▫ 25% of circulating lymphocytes are B cells Recognizing Pathogens ▫ Cells of each person has a unique set of surface recognizing molecules called antigens ▫ Lymphocytes learn how to distinguish self from non-self Allows them to recognize foreign cells and pathogens Each B and T cell has receptors that can bind with a specific antigen Only those cells that can bind the antigen are involved in the immune response • Cell-Mediated Immunity ▫ First step is to recognize the foreign antigen Antigen-presenting cell engulfs the pathogen Expresses part of the antigen on its plasma membrane Helper T cell that can bind to the antigen is activated and begins the immune response T Cells ▫ Helper T cells Start and intensify an immune response Release cytokines when activated Stimulate T and B cell clone formation Stimulate Cytotoxic T cells ▫ Cytotoxic T cells Attack and destroy specific abnormal body cells Release a cytotoxin that ruptures the cell membrane of the target cell Release cytokines that attract other lymphocytes and macrophages T Cells ▫ Memory T cells Remain to launch a strong response should the same antigen ever enter the body again ▫ Supressor T cells Suppresses the immune response Antibody-Mediated Immunity ▫ A B cell becomes activated when it Binds a specific antigen Is stimulated by cytokines by an activated Helper T cell ▫ Activated B cell forms a clone of B cells that all have the same antigen receptor ▫ Clone contains Plasma cells that produce antibodies against the specific antigen Memory B cells that allow for a stronger response with another encounter later on Antibodies (Immunoglobulins) Form antigen-antibody complexes that mark the pathogen for destruction Allows for complement fixation Binding of complement to the antigen Complement punches holes in the cell and it bursts Debris is cleaned up by phagocytes Antibodies bind bacterial toxins, blocking their action on body cells Complexes are destroyed by phagocytes • The six basic ways antibodies function: ▫ ▫ ▫ ▫ ▫ ▫ Promote inflammation Promote phagocytosis Activate the immune complement Stimulate apoptosis Agglutination Inactivate a pathogen or toxin Immune Responses • Primary immune response ▫ Occurs with the first encounter of a pathogen ▫ T and B cells make clones to destroy the antigen ▫ Produces memory cells that recognize the same antigen if it ever reenters the body • Secondary immune response ▫ Occurs with another invasion of the same antigen ▫ Memory T and B cells launch a more rapid and intense response then the primary immune response • Types of Immunity ▫ Mechanisms are grouped into two broad categories Active immunity Person is directly involved in the development of immunity Longer lasting then passive immunity Passive immunity Person is not directly involved in the development of immunity Types of Immunity ▫ Naturally acquired active immunity Person gets the disease and recovers Leaves memory T and B cells to fight later infections ▫ Artificially acquired active immunity Person receives a vaccine of dead or weakened pathogens Triggers a response that forms memory cells Booster shots cause a secondary response to boost antibodies levels Types of Immunity ▫ Naturally acquired passive immunity Infants receive mother’s antibodies through placenta and breast milk ▫ Artificially acquired passive immunity Receiving injections of antibodies produced by another person or animal Rejection of Organ Transplants • Major challenge after a transplant is organ rejection ▫ Body recognizes the new organ as non-self and attacks it • Compatibility of donor and recipient are determined before transplant • Immunosuppressive therapy is administered to prevent rejection ▫ B cells are still able to provide antibody-mediated immunity against pathogens • Bacterial and viral infections are primary causes of death ▫ 75% match is considered minimal for a transplant Disorders of the Lymphatic and Immune Systems • Disorders can be grouped according to ▫ Infectious disorders ▫ Noninfectious disorders Infectious Disorders • Acquired immune deficiency syndrome (AIDS) ▫ Caused by the human immunodeficiency virus (HIV) ▫ Attacks and kills Helper T cells ▫ Invade macrophages that serve as a reservoir for the virus AIDS ▫ Transmission occurs by Sexual intercourse Exchanges of blood Childbirth ▫ Immune defenses in the individual decrease ▫ Leads to development of secondary diseases Pneumocystis carinii Kaposi’s sarcoma ▫ No cure • Elephantiasis ▫ Tropical disease ▫ Characterized by greatly swollen legs or other body parts Lymphatic vessels are blocked by round worms ▫ Transmitted by some mosquito species • Tonsillitis ▫ Inflammation of the tonsils due to bacterial infections Noninfectious Disorders • Allergy or hypersensitivity ▫ Abnormally intense immune response to an antigen harmless to most people ▫ Allergens ▫ Sensitization to an allergen results in reactions whenever exposure occurs ▫ Reactions can be Immediate Delayed ▫ Immediate reactions Occur when allergens bind with IgE antibodies on basophil and mast cell surfaces Cells release histamine, which stimulate an inflammatory responses Localized reactions are unpleasant but not life threatening Example: hay fever, hives Systemic reactions (anaphylaxis) are life threatening Impair breathing and cause circulatory failure Example: bee stings and penicillin ▫ Delayed allergic reactions Appear 1-3 days after antigen exposure Due to cytokines from t cells Example: poison ivy • Autoimmune Diseases ▫ T and B cells recognize body tissues as nonself Produces an immune response ▫ Due possibly to change in body molecules ▫ Example: rheumatoid arthritis, multiple sclerosis • Lymphoma ▫ Any tumor of lymphatic tissue ▫ Hodgkin’s disease Malignant lymphoma Enlarged and painless lymph nodes, fatigue, fever, night sweats Chemotherapy and radiation can yield a high cure rate early
