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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