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The Lymphatic System
and Body DefensesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lecture Outline
Lymphatic System
o Three main functions• Fluid balance• Fat absorption• Defense
o Lymphatic vessels• Form a one-way system• Begins with lymphatic capillaries
Tiny, closed-ended vessels Take up excess tissue fluid (lymph)
• Vessels merge and then enter one of two ducts: Thoracic duct Right lymphatic duct
• Vessels have valves and movement of lymph depends on skeletal muscle contraction
• Edema is localized swelling caused by the accumulation of lymph
Organs, Tissues, and Cells of the Immune Systemo Primary Lymphatic Organs
• Lymphocytes originate and/or mature in these organs
• Red Bone Marrow Site of stem cells that produce blood cells In an adult, red bone marrow is found in:
Sternum Vertebrae Ribs Skull Part of the pelvic girdle Proximal heads of the humerus and femur
Lymphocytes differentiate into B and T lymphocytes
B lymphocytes mature in the red bone marrow T lymphocytes mature in the thymus
Organs, Tissues, and Cells of the Immune System
• Thymus Gland In the thoracic cavity Largest in children and shrinks as a
person ages Lobules are filled with lymphocytes Produces thymic hormones
Aids in maturation of T lymphocytes May have other functions in immunity
Critical to immunity
Organs, Tissues, and Cells of the Immune System
o Secondary Lymphatic Organs• Places where lymphocytes encounter and
bind with antigens• Spleen
Largest lymphatic organ Consists of two types of tissue:
White pulp – has a concentration of lymphocytes Red pulp – surrounds venous sinuses and is involved
in filtering blood Blood entering the spleen is filtered through
venous sinuses Lymphocytes and macrophages react to pathogens Macrophages engulf debris and remove old red blood
cells
Organs, Tissues, and Cells of the Immune System
• Lymph nodes Small structures occurring along lymphatic vessels Connective tissue
Forms a capsule Divides node into compartments
Contains nodules packed with B lymphocytes Sinus that contains T lymphocytes
Lymph passing through the sinus is filtered by macrophages
T lymphocytes fight infection and attack cancer cells
• Lymphatic nodules Concentrations of lymphatic tissue not surrounded
by a capsule Tonsils Peyer patches Appendix
Nonspecific and Specific Defenses
o Nonspecific Defenses• Barriers to entry
Physical Intact skin Mucous membranes
Chemical Sebaceous gland secretions Lysozyme in perspiration, saliva, and tears Urine pH of the stomach Normal flora
Nonspecific and Specific Defenses
• Inflammatory reaction 5 steps
1. Chemical mediators cause capillaries to dilate and become more permeable
Excess blood causes redness and increased temperature
2. Increased permeability causes fluids and proteins to escape the capillaries and cause swelling
3. Edema and clot formation “wall off” the area4. Migration of phagocytes5. Monocytes become macrophages that devour
pathogens and debris
Nonspecific and Specific Defenses
• Natural killer cells Kill virus-infected cells and tumor cells Large, granular lymphocytes No specificity and no memory
• Protective proteins Complement
Composed of blood plasma proteins Activated when pathogens enter the body Amplify the inflammatory response Bind to the surface of pathogens, ensuring that they
will be phagocytized Form a membrane attack complex that punches
holes in the walls and membranes of bacteria Interferon
Produced by virus-infected cells Produce substances that interfere with viral
replication
Nonspecific and Specific Defenses
o Specific Defenses• Respond to antigens• Lymphocytes have antigen receptors
B lymphocytes Mature in the bone marrow Give rise to plasma cells that produce
antibodies T lymphocytes
Mature in the thymus gland Directly attack cells that have nonself proteins
or regulate the immune response
Nonspecific and Specific Defenses
o Clonal Selection• When B cells encounter an antigen they are
activated to divide many times Plasma cells – mature B cell that produces
antibodies Clones
Most mature to form plasma cells Some become memory cells
Make long-term immunity possible A second exposure to the same antigen produces
a stronger, faster immune response
• Plasma cells undergo apoptosis when an infection has passed
Nonspecific and Specific Defenses
o Structure of Antibodies• Basic unit is a Y-shaped protein molecule with two
arms “heavy” polypeptide chain “light” polypeptide chain
• Chains have constant regions at the trunk of the Y• The class of antibody is determined by the structure
of the constant region• Monomers – single Y-shaped molecules• Dimers – paired Y-shaped molecules• Pentamers – clusters of 5 Y-shaped molecules linked
together
o Function of Antibodies• Neutralization• Forming immune complexes
Nonspecific and Specific Defenses
o T Cells and Cell-Mediated Immunity• Antigen must be presented to T cells by an
antigen-presenting cell• Major histocompatability (MHC) proteins
Called HLA (human leukocyte antigens) Are self proteins
• T cell compares the antigen and the self protein
Activated T cell and all daughter cells can recognize “foreign” from “self”
Will destroy cells carrying foreign antigens
• Activated T cells produce cytokines that stimulate various immune cells to perform their functions
Nonspecific and Specific Defenses
o Types of T Cells• Cytotoxic T cells
Destruction of virus-infected or cancer cells
Have storage vacuoles containing Perforin molecules
Responsible for cell-mediated immunity
• Helper T cells regulate immunity by secreting cytokines
Nonspecific and Specific Defenses
o Cytokines in Cancer Chemotherapy• Used as immunotherapeutic drugs• Interferon and interleukins are also
used as immunotherapeutic drugs
Creating and Immune Response
o Active Immunity• Often develops naturally• Immunization
Involves the use of vaccines After the first exposure, a primary
response occurs A second exposure (“booster”) produces a
secondary response
• Depends on the presence of memory cells
• Usually long-lasting
Creating and Immune Response
o Passive Immunity• Occurs when an individual is given
prepared antibodies (immunoglobulins)
• Is temporary• Can be used in the event of an
unexpected exposure to an infectious disease
Creating and Immune Response
o Monoclonal Antibodies• Every plasma cell derived from the
same B cell• Secretes antibodies against one
antigen• Can be produced in vitro• Are being used for quick and certain
diagnosis of various conditions• Used to carry radioactive isotopes or
toxic drugs to tumors
Creating and Immune Response
o Hypersensitivity Reactions• Allergies
Response to substances that are harmless to the body (allergens)
IgE-Mediated Allergic Response Immediate allergic response Caused by IgE antibodies When an allergen attaches to the IgE antibodies,
histamine is released Anaphylactic shock occurs when the allergen has
entered the blood stream T-Cell Mediated Allergic Response
Initiated by memory T-cells at the site of allergen contact
Regulated by cytokines
Creating and Immune Response
• Tissue Rejection Transplanted tissue is recognized as not
“self” Cytotoxic T cells cause disintegration of
the transplanted tissue Can be controlled by:
Selecting organs that have the same type of HLA antigens as those of the recipient
Administering immunosuppressive drugs
Creating and Immune Response
• Autoimmune Diseases Cytotoxic T cells or antibodies attack the
body’s own cells Cause is unknown Examples:
Myasthenia gravis Multiple sclerosis Systemic lupus erythematosus Rheumatoid arthritis
No cures, but can be managed with medications
Creating and Immune Response
• Immune Deficiency The immune system is unable to protect
the body from disease Can be acquired or genetic Without treatment, common infections
can be fatal
Effects of Aging
o Aging people become more susceptible to infections and disorders
o Thymus gland degenerates and number of T cells decreases
o B cells sometimes do not form clones
o Incidence of autoimmune diseases increases
o Response to vaccines is decreased
Homeostasis
o The lymphatic system helps the following:• The digestive system by absorbing fat• The cardiovascular system by absorbing lymph• The immune system in protection against infectious
diseases
o Nonspecific immune responses are dependent on:
• The skin• Mucous membranes of the respiratory tract, the
digestive tract, the reproductive and urinary systems
o Specific defenses are dependent on blood cellso There is a strong connection between the
immune, nervous, and endocrine systems