Lymphatic system And immunity

Lymphatic pathways  Collecting ducts  Thoracic duct  Larger and longer collecting duct  Lower limbs, abdominal regions, left upper limb, and left side of the thorax, head, and neck and empties into the left subclavian vein  Right lymphatic duct  Right side of the head and neck, right upper limb, and right thorax and empties into the right subclavian vein  Enters the venous system and becomes part of the plasma just before blood returns to right atrium

Tissue fluid and lymph  Tissue fluid formation  Originates from blood plasma and is composed of water and dissolved substances that leave blood capillaries by diffusion and filtration  Lymph formation and function  increased pressure forces tissue fluid into lymphatic capillaries where it becomes lymph  Lymph returns small proteins back to bloodstream  Transports foreign particles to lymph nodes  Lymph movement is influenced by muscle movement and breathing movements

Lymph nodes  Located along the lymph pathways  Contain large numbers of lymphocytes and macrophages that fight invading microorganisms  Hilum- indented region where blood vessels and nerves join the node and efferent lymphatic vessels exit  Lymph nodules- masses of lymphoctes and macrophages that are the structural unit  Lymphatic sinuses- complex network of chambers and tunnels through which lymph circulates  Area where macrophages are highly concentrated

Lymph node functions  Two primary functions  Filtering potentially harmful particles from lymph before returning it to the bloodstream  Immune surveillance provided by lymphocytes and macrophages  Centers for lymphocyte production  Attack infecting viruses, bacteria and other microorgansims  Macrophages engulf and destroy foreign substances, damaged cells, and cellular debris

Thymus  Contain abundant lymphocytes  Some mature into T cells  Leave the thymus and provide immunity  Epithelial cells secrete thymosin  Stimulates maturation of T cells after they leave the thymus and migrate to other lymphatic tissues

Spleen  Largest lymphatic organ  Contain two types of tissue  White pulp  Distributed throughout the spleen in tiny islands  Composed of splenic nodules and contain many lymphoctyes  Red pulp  Fills remaining sinuses and surround venous sinuses  Contains numerous red blood cells, lymphocytes, and macrophages

Spleen cont.  Phagocytic macrophages remove old, fragile blood cells and cellular debris  Also engulf and destroy foreign particles  Filters blood

Body defenses  Two main types  Nonspecific defenses  Respond rapidly  Specific defenses  Slower to respond  Work together to protect the body against infection

Nonspecific defenses  Species resistance  The fact that a given kind of species develops diseases that are unique to it  Mechanical barriers  Skin and mucous membranes  Provide a first line of defense

Nonspecific defense cont. Second line defense  Chemical barriers  Certain cells produce interferons  Fever  Elevated body temperature  Causes liver and spleen to hide iron  Phagocytic cells attack more vigorously

Nonspecific defenses  Inflammation  Body’s response to injury or infection  Produces localized redness, swelling, heat, and pain  Infected cells produce chemicals attracting white blood cells  mass of white blood cells may form a thick fluid called pus  fibrinogen and other clotting factors enclosing the area to prevent spread of pathogens  Phagocytosis  Remove foreign particles from lymph as it moves through the lymphatic system

Specific defenses-immunity third line defense  Antigens  Any substance that is capable of exciting our immune system and provoking an immune response  Lymphocyte functions  T cells and B cells respond to antigens

Specific defense  Antibodies  Immunoglobulin G  In plasma and tissue fluid  Effective against toxins, bacteria and viruses  Activates immune system enzymes--complement  Immunoglobulin A  In exocrine gland secretions  Immunoglobulin M  Develops in plasma in response to antigens  Immunoglobulin D  Surface of most B cells and activates B cells  Immunoglobulin E  Appears in exocrine secretions  Associated with allergic reactions

Specific defenses  Immune response  Primary immune response- antibodies are released and transported throughout the body destroying antigen bearing agents  Some B cell become dormant memory cells producing a secondary immune response  Allergic reactions  An immune attack against a nonharmful substance  Can damage tissue

Transplant and tissue rejection  The danger the immune system poses to transplanted tissue is that the recipient’s cells may recognize the donor’s tissue a foreign and attempt to destroy transplanted tissue  Immunosuppresive drugs are used to reduce rejection of transplanted tissue  Interfere with recipient’s immune response by suppressing formation of antibodies or production of T cells  Leaves unprotected against infections

autoimmunity  Does not distinguish self from non-self producing autoantibodies  Attack and damage tissues and organs  Specific nature of autoimmune disorder depends on the cell type that are the target of the immune attack  Virus may borrow proteins from host cell’s surface and incorporate them on its surface  T cell escape education of self in thymus  Nonself antigen resembles a self antigen