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Chapter 22: The Lymphatic System and Immunity … · Copyright 2009, John Wiley & Sons, Inc....
Transcript of Chapter 22: The Lymphatic System and Immunity … · Copyright 2009, John Wiley & Sons, Inc....
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Copyright 2009, John Wiley & Sons, Inc.
Chapter 22: The Lymphatic
System and Immunity
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Copyright 2009, John Wiley & Sons, Inc.
Immunity or Resistance
Ability to ward off damage or disease through our
defenses
2 types of immunity
Innate or nonspecific immunity – present at birth
No specific recognition of invaders, no memory
component
1st and 2nd line of defenses
Adaptive or specific immunity
Specific recognition of invaders with a memory
component
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Lymphatic system structure and function
Consists of lymph, lymphatic vessels,
structures and organs containing lymphatic
tissue, red bone marrow
Functions of the lymphatic system
1. Drain excess interstitial fluid
2. Transport dietary lipid
3. Carry our immune responses
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Components of the Lymphatic System
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Lymphatic vessels and lymph circulation
Vessels begin as lymphatic capillaries
Closed at one end
Unite to form large lymphatic vessels
Resemble veins in structure but thinner
walls and more valves
Passes through lymph nodes
Encapsulated organs with masses and B
and T cells
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Lymphatic capillaries
Slightly large diameter that blood capillaries
Unique one-way structure
Permits interstitial fluid to flow in but not out
Anchoring filaments pull openings wider when
interstitial fluid accumulates
Small intestine has lacteal for dietary lipid
uptake
Chyle is lymph with lipids
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Lymphatic Capillaries
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Lymph trunks and ducts
Vessels unite to form lymph trunks
Principal trunks are the lumbar, intestinal,
bronchomediastinal, subclavian and jugular
Passes from lymph trunks into 2 main
channels (thoracic and right lymphatic ducts)
before draining into venous blood
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Routes for drainage of lymph
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Formation and flow of lymph
More fluid filters out of blood capillaries than
returns to them by reabsorption
Excess filtered fluid – about 3L/day – drains into
lymphatic vessels and become lymph
Important function of lymphatic vessels to return
lost plasma proteins to blood stream
Contain valves
Same 2 “pumps” aiding venous return also used
Skeletal muscle pump – milking action
Respiratory pump – pressure changes during breathing
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Relationship of the Lymphatic System to
the Cardiovascular System
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Lymphatic tissues and organs
2 groups based on function
1. Primary lymphatic organs
Sites where stem cells divide and become
immunocompetent
Red bone marrow and thymus
2. Secondary lymphatic organs
Sites where most immune response occurs
Lymph nodes, spleen, lymphatic nodules
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Thymus and Medulla
Thymus Outer cortex composed of large number of T cells
Immature T cells migrate here from red bone marrow where they proliferate and begin to mature
Dendritic cells derived from monocytes assist in T cell maturation
Specialized epithelial cells help educate T cells through positive selection – only about 25% survive
Macrophages clear out dead and dying cells
Medulla
More mature T cells migrate here from cortex
More epithelial cells, dendritic cells and macrophages
Thymus shrinks with age from 70g in infants to 3g in old age
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Thymus
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Lymph nodes
Located along lymphatic vessels
Scattered throughout body
Stroma – supporting connective tissue
Capsule, trabeculae, reticular fibers and fibroblasts
Parenchyma – functional part
Outer cortex – aggregates of B cells called lymphatic nodules (follicles) – site of plasma cell and memory B cell formation
Inner cortex – mainly T cells and dendritic cells
Medulla – B cells, antibody producing plasma cells from cortex, and macrophages
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Structure of a Lymph Node
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Lymph
Lymph flows through a node in 1 direction only Enters through afferent lymphatic vessels
Directs lymph inward
Lymph enters sinuses (irregular channels)
Into medulla
Medullary sinuses drain into efferent lymphatic vessels
Conveys lymph, antibodies and activated T cells out of the node
Lymph nodes function as a filter Foreign substances trapped
Destroyed by macrophages or immune response of lymphocytes
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Spleen
Largest single mass of lymphatic tissue in the body
Stroma – capsule, trabeculae, reticular fibers, and fibroblasts
Parenchyma
White pulp – lymphatic tissue (lymphocytes and macrophages)
B cells and T cells carry out immune function
Red pulp
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Red Pulp
Red pulp – blood-filled venous sinuses and
splenic (Bilroth’s) cords – red blood cells,
macrophages, lymphocytes, plasma cells, and
granulocytes
Macrophages remove ruptured, worn out or
defective blood cells
Storage of up to 1/3 of body’s platelet supply
Production of blood cells during fetal life
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Structure of the Spleen
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Lymphatic nodules
Not surrounded by a capsule
Scattered throughout lamina propria of
mucous membranes lining GI, urinary,
reproductive tract
Mucosa-associated lymphatic tissue (MALT)
of respiratory tract
Most small and solitary
Some larger – tonsils, Peyer’s patches,
appendix
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Innate immunity
First line of defenses: Skin and mucous membranes
Provide both physical and chemical barriers
Physical barriers Epidermis – closely packed, keratinized cells
Periodic shedding
Mucous membranes
Mucus traps microbes and foreign substances
Nose hairs trap and filter
Cilia of upper respiratory tract propel trapped particles up and out
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Innate Immunity
Fluids Lacrimal apparatus of eye
Washing action of tears
Lysozyme breaks down bacterial cell walls – also present in saliva, perspiration, nasal secretions, and tissue fluids
Saliva washes mouth
Urine cleanses urinary system
Vaginal secretions, defecation and vomiting
Chemicals Sebaceous (oil) glands secrete sebum – protective film,
acid
Perspiration, gastric juice, vaginal secretions – all acidic
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Internal Defenses
Natural Killer (NK) cells Lymphocyte but not a B or T cell
Ability to kill wide variety of infected body cells and certain tumor cells
Attack any body cell displaying abnormal or unusual plasma membrane proteins
Can release perforin (makes perforations) or granzymes (induce apoptosis)
Phagocytes Neutrophils and macrophages (from monocytes)
Migrate to infected area
5 steps in phagocytosis
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Inflammation
Nonspecific, defensive response of body to tissue
damage
4 signs and symptoms – redness, pain, heat and
swelling
Attempt to dispose of microbes, prevent spread,
and prepare site for tissue repair
3 basic stages
Vasodilation and increased blood vessel permeability
Emigration
Tissue repair
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Vasodilation and increased permeability of
blood vessels
Increased diameter of arterioles allows more blood flow through area bringing supplies and
removing debris
Increased permeability means substances
normally retained in the blood are permitted to
pass out – antibodies and clotting factors
Histamine, kinins, prostaglandins (PGs),
leukotrienes (LTs), complement
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Inflammation
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Emigration of phagocytes
Depends on chemotaxis
Neutrophils predominate in early stages but
die off quickly
Monocytes transform into macrophages
More potent than neutrophils
Pus – pocket of dead phagocytes and
damaged tissue
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Adaptive immunity
Ability of the body to defend itself against
specific invading agents
Antigens (Ags) – substances recognized as
foreign and provoking an immune response
Distinguished from innate immunity by
Specificity
Memory
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Maturation of T cells and B cells
Both develop from pluripotent stem cells
originating in red bone marrow
B cells complete their development in red bone marrow
T cells develop from pre-T cells that migrate from red
bone marrow to the thymus
Helper T cells (CD4 T cells) and cytotoxic T cells (CD8 T
cells)
Immunocompetence – ability to carry out adaptive
immune response
Have antigen receptors to identify specific antigen
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2 types of adaptive immunity
Cell-mediated
Cytotoxic T cells directly attack invading antigens
Particularly effective against intracellular pathogens, some
cancer cells and foreign tissue transplants
Antibody-mediated
B cells transform into plasma cells making antibodies (Abs) or
immunoglobulins
Works against extracellular pathogens in fluids outside cells
Helper T cells aid in both types
2 types of immunity work together
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Antigens
Antigens have 2 characteristics
Immunogenicity – ability to provoke immune response
Reactivity – ability of antigen to react specifically with antibodies it provoked
Entire microbes may act as antigen
Typically, just certain small parts of large antigen molecule triggers response (epitope or antigenic determinant)
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Pathways of antigen processing
B cells can recognize and bind to antigens
T cells must be presented with processed
antigens
Antigenic proteins are broken down into peptide
fragments and associated with MHC molecules
Antigen presentation – antigen-MHC complex
inserted into plasma membrane
Pathway depends on whether antigen is outside or
inside body cells
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Antibodies (Ab)
Can combine specifically with epitope of the antigen that
triggered its production
Belong to group of glycoproteins called globulins
Ab are immunoglobulins (Igs)
4 polypeptide chains – 2 heavy (H) chains, 2 light (L)
chains
Hinge region – antibody can be T shape or Y shape
Variable (V) region at tips of each H and L chain
2 antigen-binding sites - bivalent
Constant (C) region – remainder of H and L chain
Same in each 5 classes – determines type of reaction
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Antibody actions
Neutralizing antigen
Immobilizing bacteria
Agglutinating and precipitating antigen
Enhancing phagocytosis
Activating complement
Defensive system of over 30 proteins
Destroy microbes by causing phagocytosis, cytolysis, and
inflammation
Acts in a cascade – one reaction triggers another
3 different pathways ass activate C3
C3 then begins cascade that brings about phagocytosis,
cytolysis, and inflammation