The Lymphatic System And Immunity1

The Lymphatic System and Immunity

Introduction
Pathogens: microorganisms responsible for human and animal diseases
Bacteria
Viruses
Fungi
Parasites
Lymphatic system
Keeps us alive and healthy

Defenses
First line of Defense
- Skin and the linings of the respiratory, digestive, and urinary systems
- Involves chemical deterrents like a) skin , for instance produces a slightly acidic secretion that impairs bacterial growth.
b) stomach lining releases hydrochloric acid that destroys ingested bacteria.
c) saliva contains an enzyme that dissolves the cell wall of bacteria, killing them.

Defenses Cont
Second line of defense
chemical and cellular agents that take up the battle from this point
A cut or abrasion, for instance, results in the inflammatory response.
Characteristics : 1) Redness, 2)swelling, 3)pain, 4) Heat

Chemical substances
Histamine is a chemical released by injured tissue causes arterioles in the damaged area to expand or dilate thereby allowing more blood to flow into the region.
Another chemical safe guard not part of the inflammatory response, is a group of small proteins known as the interferons.
Interferon's are released from cells infected by viruses and they help to halt the spread of viruses from one cell to another

The Immune System
3rd Line of Defense
Lymphocytes are a key component of the immune system. They circulate in the blood and lymph and also take up residence under linings of the respiratory and digestive systems. Many also reside in the spleen, thymus,lymph nodes, and tonsils, known as lymphoid organs

Organization of Lymphatic System
3 components
Lymphatic vessels
Fluid (lymph)
Lymphoid organs

Functions of Lymphatic System
Production, maintenance, distribution of lymphocytes
Respond to presence of:
Invading pathogens
Abnormal body cells (virus-infected cells, cancer cells)
Foreign proteins (toxins released by bacteria)
Return of fluid and solutes from peripheral tissues to blood
Distribution of hormones, nutrients, and waste products from tissues of origin to general circulation

Types of Lymphocytes
T cells (Thymus dependent)
80% of circulating lymphocytes
Cytotoxic T cells
Directly attack foreign cells or body cells infected by viruses (cell-mediated immunity)
Helper T cells
Stimulate activities of both B and T cells
Suppressor T cells
Inhibit both T and B cells

Types of Lymphocytes
B cells (Bone-marrow derived)
10-15% circulating lymphocytes
Plasma cells
Responsible for production and secretion of antibodies (immunoglobulins)
Responsible for antibody-mediated immunity
NK cells (Natural Killer)
5-10%
Attack foreign cells, normal cells infected with viruses, and cancer cells
Immunological surveillance

Lymphoid Nodules
Masses of lymphoid tissue w/o a capsule
Increase and decrease size depending on # lymphocytes present
Found beneath epithelial lining of organs in:
Respiratory system
Digestive system
Tonsils
Peyer’s patches
Urinary system

Lymphoid Organs: Lymph Nodes

Lymphoid Organs: Thymus

Lymphoid Organs: Spleen

The Lymphatic System and Body Defenses
Nonspecific Defenses
Do not distinguish one threat from another
Physical barriers
Phagocytic cells
Immunological surveillance
Interferons
Complement
Inflammation
Fever
Specific Defenses
Protect against particular threats
Develop after birth
Dependent on activity of lymphocytes
B cells
T cells

Macrophage

Apoptosis and Macrophages

Immune System

Properties of Immunity
Specificity
Versatility
Memory
Tolerance

Overview of Immune Response

Specific Defense: The Immune Response
Respond to specific antigens
T cells
Cell-mediated immunity (cellular immunity)
Provide defense against abnormal cells and pathogens in living cells
B cells
Antibody-mediated immunity (humoral immunity)
Provide a defense against antigens and pathogens in body fluids

Forms of Immunity
Either innate or acquired
Innate
Genetically determined
Acquired
Active or Passive
Active Immunity
Naturally acquired immunity
Induced active immunity
Passive Immunity
Induced passive immunity
Natural passive immunity

T Cells
Once activated, T cells divide and differentiate in to cells with specific function in immune response
Cytotoxic T cells
Helper T cells
Memory T cells
Suppressor T cells

Cytotoxic T Cells
Responsible for cell-mediated immunity
Track down and attack bacteria, fungi, protozoa, or foreign transplanted tissue
Also called Killer T cells

Helper T Cells
Activated by exposure to antigens bound to Class II MHC proteins
Activated  divide to produce
Active Helper T cells and memory cells
Release variety of cytokines that:
Coordinate specific and nonspecific defenses
Stimulate cell mediated and antibody-mediated immunity

Memory T Cells
During cell division for both cytotoxic and helper T cells, some develop into memory cells
Remain in reserve
If same antigen attacks 2 nd time, memory T cells immediately differentiate into cytotoxic T cells and helper T cells
Allows for more rapid and effective immune response

Suppressor T Cells
When activated, depress responses of other T and B cells
Does not occur immediately
Takes much longer for these cells to become activated
Act after initial immune response

B Cells and Antibody-Mediated Immunity: B Cell Activation
Each B cell carries its antibody molecules in its cell membrane
When bacterium first enters the body, B cells programmed to respond to the unique proteins found in the bacterium’s cell membrane bind to it

B Cell Activation
Activated B cells divide several times
Produce daughter cells that differentiate into:
Plasma cells
Synthesize and secrete large numbers of antibodies on surface of sensitized B cells
Memory cells
Similar to memory T cells
If exposed to same antigen, will differentiate into plasma cells

Classes of Antibodies (Immunoglobins Igs)
IgG
Largest and most diverse
Resist many viruses, bacteria, bacterial toxins
Can cross placenta
What type of immunity is that?
IgM
Circulate; attack bacteria
IgA
Found in exocrine secretions
Ex?
Attack pathogens before they enter the body
IgE
When bound to antigen, stimulates basophils and mast cells to release chemicals to stimulate inflammation
IgD
Attached to B cell and involved in their activation

The Complement System

Antibody Function
Neutralization
Agglutination and Precipitation
Activation of a complement
Attraction of phagocytes
Enhancement of phagocytosis
Stimulation of inflammation

Primary and Secondary Responses to Antigen Exposure

The Lymphatic System And Immunity1

by krismd on Dec 08, 2008

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