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The Lymphatic System and Body Defenses
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The Lymphatic System
• Consists of two semi-independent parts– Lymphatic vessels– Lymphoid tissues and organs
• Lymphatic system functions– Transport fluids back to the blood– Body defense and resistance to disease
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Lymphatic Characteristics• Lymph – excess tissue fluid carried by
lymphatic vessels• Properties of lymphatic vessels
– One way system toward the heart– No pump– Lymph moves toward the heart
• Milking action of skeletal muscle• Rhythmic contraction of smooth muscle in vessel
walls
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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
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Lymphatic Vessels
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Lymphatic Vessels• Lymphatic collecting
vessels– Collects lymph from
lymph capillaries– Carries lymph to and
away from lymph nodes
– Returns fluid to circulatory veins near the heart at the right lymphatic duct or thoracic duct
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Lymph• Lymph returned to the blood is composed of:
– Water– Blood cells– Proteins
• Harmful materials that enter lymph vessels– Bacteria– Viruses– Cancer cells– Cell debris
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Lymph Nodes
• Filter lymph before returning to the blood• Contain defense cells:
– Macrophages – engulf and destroy foreign substances
– Lymphocytes – provide immune response to antigens
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Lymph Nodes
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Lymph Node Structure
• Most are kidney-shaped, <1 inch long
• Cortex - outer part– Contains follicles
with lymphocytes• Medulla - Inner part
– Contains phagocytic macrophages
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The Flow of Lymph Through Nodes
• 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
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Other Lymphoid Organs
• Several other organs contribute to lymphatic function:– Spleen– Thymus– Tonsils– Peyer’s patches
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The Spleen
• Located on the left side of the abdomen• Filters blood – cleanses blood of bacteria,
viruses and debris• Destroys worn out blood cells• Stores platelets• Acts as a blood reservoir• Forms blood cells in the fetus (hematopoietic) • Produces lymphocytes only in the adut spleen
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The Thymus
• Located low in the throat, overlying the heart
• Functions at peak levels only during childhood
• Produces hormones (like thymosin) to program lymphocytes
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Tonsils
• Small masses of lymphoid tissue around the pharynx
• Traps and removes bacteria and other foreign materials
• Tonsillitis = is caused by congestion with bacteria
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Peyer’s Patches
• Found in the wall of the small intestine• Resemble tonsils in structure• Capture and destroy bacteria in the
intestine
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Mucosa-Associated Lymphatic Tissue (MALT)
• Includes:– Peyer’s patches– Tonsils– Other small accumulations of lymphoid tissue
• Acts as a sentinal to protect respiratory and digestive tracts from foreign matter
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Body Defenses
• The body is constantly in contact with bacteria, fungi, and viruses
• The body has two defense systems for foreign materials– Nonspecific defense system– Specific defense system
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Body Defenses• Nonspecific defense system
– Mechanisms protect against a variety of invaders– Responds immediately to protect body from foreign
materials– Provided by body surface coverings
• intact skin, mucous membrane, cellular proteins and inflammatory response.
– Specialized human cells– Chemicals produced by the body
• Specific defense system– Known as the immune system– Specific defense is required for each type of invader
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Body Defenses
Figure 12.6
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Surface Membrane Barriers1st Line of Defense
• The skin– Physical barrier to foreign materials– pH of the skin is acidic to inhibit bacterial growth
• Sebum is toxic to bacteria• Vaginal secretions are very acidic
• Stomach mucosa– Secretes hydrochloric acid– Has protein-digesting enzymes
• Saliva and lacrimal fluid contain lysozyme• Mucus traps microogranisms in digestive and
respiratory pathways
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Defensive Cells• Phagocytes (neutrophils and macrophages)– Engulfs foreign material
into a vacuole– Enzymes from lysosomes
digest the material• Natural killer cells
– Can lyse and kill cancer cells
– Can destroy virus- infected cells
Figure 12.7a
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Events of Phagocytosis
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Inflammatory Response – 2nd Line of Defense
• Triggered when body tissues are injured• Produces four cardinal signs
– Redness– Heat– Swelling– Pain
• Results in a chain of events leading to protection and healing
Inflammatory Response
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Functions of the Inflammatory Response
• Prevents spread of damaging agents
• Disposes of cell debris and pathogens
• Sets the stage for repair
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The Inflammatory Response• Begins with a chemical ‘alarm”- Histamines when
cells are injured• Blood vessels dilate increases blood flow to area
causing redness and heat. • Capillary beds become permeable becoming
leaky, which increases edema• Pain receptors are activated• Phagocytes and WBC are attracted to the area:
– Chemotaxis = cells follow chemical gradient
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Antimicrobial Chemicals
• Complement proteins– 20 active plasma proteins circulating in the
blood– Attach to foreign cells and fight against them.
• Interferon– Secreted proteins of virus-infected cells– Bind to healthy cell surfaces to inhibit viruses
binding
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Fever• Abnormally high body temperature• Systemic response to invading microorganisms• Heat regulated by Hypothalmus ‘thermostate’ -
reset upwards by pyrogens (secreted by white blood cells)
• High temperatures inhibit the release of iron and zinc from liver and spleen needed by bacteria
• Fever also increases the speed of tissue repair
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Specific Defense: The Immune System 3rd Line of Defense
• Antigen specific – recognizes and acts against particular foreign substances
• It stalks and eliminates any invading pathogen• Systemic – not restricted to the initial infection
site• Has memory – recognizes and mounts a
stronger attack on previously encountered pathogens
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2 Types of Immunity
• Humoral immunity– Its Antibody-mediated immunity where
antibodies are present in the body’s fluids– Cells produce chemicals for defense
• Cellular immunity– Cell-mediated immunity where lymphocytes
themselves defend the body.– Cells are the protective factors that target
virus infected cells
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Antigens (Nonself = foreign intruders)
• Antigen = any substance capable of exciting the immune system and provoking an immune response
• Examples of common antigens: – foreign proteins, nucleic acids, large carbohydrates,
pollen grains, microorganisms• As the immunity system develops, it inventories
all these proteins so it recognizes them as self.
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Self-Antigens
• Human cells have many surface proteins• Our immune cells do not attack our own
proteins• Our cells in another person’s body can
trigger an immune response because they are foreign– Restricts donors for transplants
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Allergies• Many small molecules (called haptens or
incomplete antigens) are not antigenic, but link up with our own proteins
• The immune system may recognize and respond to a protein-hapten combination
• The immune response is harmful rather than protective because it attacks our own cells
• Haptens are found in chemicals, poison ivy, animal dander, detergens, hair dyes, cosmetics, housefold/industrial products.
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Crucial Cells of the Immune System
• 2 types of Lymphocytes– B lymphocytes (B cells) become immunocompetent in
the bone marrow; produce antibodies, oversee humoral immunity.
– T lymphocytes (T cells) become immunocompetent in the thymus;
– Originate from hemocytoblasts in the red bone marrow• Macrophages
– Arise from monocytes– Become widely distributed in lymphoid organs– Do not respond to specific antigens but help
lymphocytes do that
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Activation of Lymphocytes
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Secondary Response
• Memory cells are long-lived
• A second exposure causes a rapid response
• The secondary response is stronger and longer lasting
Figure 12.13
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Active Immunity• Your B cells
encounter antigens and produce antibodies
• Active immunity can be naturally or artificially acquired (vaccines
Figure 12.14
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Passive Immunity
• Antibodies are obtained from someone else– From a mother to her fetus– Artificially from immune serum or gamma
globulin• Immunological memory does not occur• Protection provided by “borrowed
antibodies” is short-lived
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Monoclonal Antibodies• Antibodies prepared for clinical testing or
diagnostic services• Produced from descendents of a single cell
line and exhibit specificity for only one antigen.
• Examples of uses for monoclonal antibodies– Diagnosis of pregnancy– Treatment after exposure to hepatitis and rabies
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Antibodies (Immunoglobulins) (Igs)
• Soluble proteins secreted by B cells (plasma cells)
• Carried in blood plasma• Capable of binding specifically to an
antigen
Figure 12.15a
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Antibody Structure• Four amino acid
chains linked by disulfide bonds
• Two identical amino acid chains are linked to form a heavy chain
• The other two identical chains are light chains
• Specific antigen-binding sites are present
Figure 12.15b
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Antibody Classes
• Antibodies of each class have slightly different roles
• Five major immunoglobulin classes– IgM – can fix complement– IgA – found mainly in mucus– IgD – important in activation of B cell– IgG – can cross the placental barrier– IgE – involved in allergies
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T Cell Clones• Cytotoxic T cells
– Specialize in killing infected cells– Insert a toxic chemical (perforin)
• Helper T cells– Recruit other cells to fight the invaders– Interact directly with B cells
• Suppressor T cells– Release chemicals to suppress the activity of T and B
cells– Stop the immune response to prevent uncontrolled
activity• A few members of each clone are memory cells
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Organ Transplants and Rejection
• Major types of grafts– Autografts – tissue transplanted from one site
to another on the same person– Isografts – tissue grafts from an identical
person (identical twin)– Allografts – tissue taken from an unrelated
person– Xenografts – tissue taken from a different
animal species (Bovine)
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Organ Transplants and Rejection
• Autografts and isografts are ideal donors• Xenografts are never successful• Allografts are more successful with a
closer tissue match
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Disorders of the Immunity
• Allergies (Hypersensitivity)• Immunodeficiencies• Autoimmune Diseases
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Disorders of Immunity: Allergies (Hypersensitivity)
• Abnormal, vigorous immune responses• (2) Types of allergies:
1)- Immediate hypersensitivity• Triggered by release of histamine from IgE
binding to mast cells• Reactions begin within seconds of contact with
allergen• Anaphylactic shock – dangerous, systemic
response
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Disorders of Immunity: Allergies (Hypersensitivity)
2) Delayed hypersensitivity• Triggered by release of lymphokines from
activated helper T cells• Symptoms usually appear 1–3 days after
contact with antigen
Example: Contact dermititis
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Disorders of Immunity: Immunodeficiencies
• Production or function of immune cells or complement is abnormal
• May be congenital or acquired• Includes AIDS – Acquired Immune Deficiency
Syndrome SCID – Severe combined immunodeficiency disease (bubble babies)
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Autoimmune Diseases• The immune system does not distinguish
between self and nonself• The body produces antibodies and sensitized T
lymphocytes that attack its own tissues
Multiple sclerosis – myelin sheath of brain & spinal cord are destroyedMyasthenia gravis – impairs communication between nerves & skeletal musclesGlomerulonephritis – impairment of renal function
Type I diabetes – destroys pancreatic beta cells that produce insulinRheumatoid arthritis – destroys jointsSystemic lupus erythematosus – affects kidney, heart, lung & skin
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Developmental Aspects of the Lymphatic System
• Lymphoid organs are poorly developed before birth, except the thymus & spleen
• A newborn has no functioning lymphocytes at birth; only passive immunity from the mother
• If lymphatics are removed or lost, severe edema results, but vessels grow back in time