Chapter Summary One of the least recognized of the body systems the lymphatic system has been gaining ground in recognition and understanding over the past two decades largely due to research into AIDS cancer and autoimmune disorders It is very important in fighting disease and maintaining healthy homeostatic balance within nearly all body system Although at first unfamiliar to most this system quickly piques their interest as a lifesaving system that deserves their attention The two semi independent parts of the lymphatic system are presented first beginning with the lymphatic vessels and followed by the lymphoid tissues and organs Next is a full description of body defenses beginning with an explanation of the nonspecific defenses such as fever and the inflammatory response which hinder the entry and spread of pathogens Specific defenses then follow with special focus on the antigen antibody response Under immune system regulation they destroy foreign cells The cells of the immune system are also outlined and explained The next section of the chapter discusses the two types of immune response Humoral antibody mediated immunity is described first highlighting the various roles of B cells and explaining the differences between active and passive types of humoral immunity Cellular cell mediated immunity is presented next along with a description of the role T cells play in this type of immune response The final section of this chapter discusses homeostatic imbalances of the immune system Organ transplantation and its associated risk of rejection are explained along with allergies immunodeficiencies and autoimmune disorders Finally in discussing the developmental aspects of the lymphatic system there is an explanation that our immune system begins to wane in later life making us more susceptible to cancer as well as autoimmune and immunodeficiency diseases The Lympthatic System Consists of two parts Lymphatic vessels Lymphoid tissues and organs Lymphatic system functions Transports escaped fluids back to the blood Plays essential roles in body defense and to disease Also has a role in digestion Developmental Aspects of the Lymphatic System and Body Except for the thymus and spleen the lymphatic organs are poorly defenses developed before birth A newborn has no functioning lymphocytes at birth only passive immunity from the mother If lymphatic s are removed or lost severe edema results but vessels MAY grow back in time Central Lymphoid Tissue Bone Marrow Thumus Central Lymphoid Tissue Bone Marrow o Hematoppoetic stem cells precursor for all bood cells o Leukocytes except T lymphocytes fully develop here Thymus o T lymphocytes migrate from bone marrow to thymus o Develop maturity in thymus Peripheral Lympoid Tissue Spleen lymph nodes tonsils adenoid appendix Peyer s patches Collections of B cells T cells and macrophages Function to trap microorganisms and foreign particles Works to expose them to leukocytes in high concentrations Spleen and lymph nodes filter blood and lymph Lymphoid Organs That Contribute to Lymphatic Function SPLEEN Located on the left side of the abdomen Filters blood and destroys worn out blood cells Forms blood cells in the fetus Acts as a blood reservoir THYMUS TONSILS Located low in the throat overlying the heart Functions at peak levels only during childhood Produces hormones like thymosin to program lymphocytes Masses of lymphoid tissue around the pharynx Trap and remove bacteria and other foreign materials Tonsillitis is caused by congestion with bacteria PEYER S PATCHES Found in the wall of the small intestine capture and destroy bacteria in the intestine Lymph Nodes Filters lymph fluid before it is returned to the BLOOD Defense cells within lymph nodes Macrophages engulf and destroy foreign substances Lymphocytes provide immune response to antigens Some harmful materials that may enter lymph vessels Bacteria Viruses Cancer cells Cell debris Protists Worms Fungi Lymph Node Structure o Most are kidney shaped and less than one inch long o CORTEX The outer part Contains follicles that house collections of lymphocytes o MEDULLA The inner part Contains phagocytic macrophages Lymphatic Characteristics edema swelling of the tissue Properties of lymphatic vessels Lymph fluid carried by lymphatic vessels One way system toward the heart No PUMP Lymph moves toward the heart o Squeezing motion of skeletal muscle o Rhythmic contraction of smooth muscle in vessel walls Flow of Lymph Through Nodes Lymphatic Vessels 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 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 Fluid is forced along the vessel Lymphatic Vessels Lymphatic collecting vessels Collect lymph from lymph capillaries Carry lymph to and away from lymph nodes Return fluid to circulatory veins near the heart Rightly lymphatic duct Thoracic duct THE IMMUNE SYSTEM Body Defenses The Immune System The body is constantly in contact with protists bacteria fungi and viruses The body has two defense systems for foreign materials 1 Innate defense system nonspecific defense system o Mechanisms protect against a variety of invaders o Responds immediately to protect body from foreign materials 2 Adaptive defense system specific defense system is specific defense is required for each type of invader We can develop immunity or specific resistance to certain pathogens Innate Nonspecific Body Defenses First Line of Defense Physical Barriers Skin is a physical barrier to foreign materials Mucous membranes Mucus traps microogranisms in digestive and respiratory pathways Chemical Barriers Secretions from sebaceous and sweat glands salty sweat sebum is toxic to bacteria Sebaceous glands secrete oily substance into hair follicles Urine Vaginal secretions are acidic pH of the skin is acidic to inhibit bacterial growth Stomach mucosa and secretes hydrochloric acid also has protein digesting enzymes Lysozyme in tears sweat saliva etc can break down bacteria Innate Nonspecific Body Defenses First Line of Defense Nonspecific Immune System s General Response Flu like Symptoms Fever Runny nose and watery eyes Fluid and mucus in lungs Diarrhea
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