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 Four signs:

Redness Heat Swelling Pain

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

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