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Lines the digestive, respiratory and genitourinary tracts

Bars entry of harmful microbes

Also counters pathogens with chemical defenses

*saliva, tears, and mucous secretions bathe the surface of exposed epithelia washingaway many potential invaders

EX: LYSOZYME- an enzyme that digest the cell walls of many bacteria

and destroys many microbes entering the upper respiratory system and

the openings around the eyes.

MUCOUS MEMBRANE

PERSONAL SHIELDS


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Internal defense mechanisms that are nonspecific depend mainly on PHAGOCYTOSIS:

* PHAGOCYTOSIS is the ingestion of invading particles by certain types of white blood cells *

Neutrophils comprise about 60% to 70% of all white blood cells

Attracted by chemical signals, neutrophils can leave the blood and enter infected tissue byamoeboid movement.

Once there they can DESTROY the microbes!!!

(this migration of a chemical attractant is called chemotaxis)

**Neutrophils tend to self-destruct as they destroy foreign invaders so theyre average life is onlyabout a few days.

Monocytes (only make up about 5% of the WBC) strengthen phagocytic defense

Monocytes mature intoMACROPHAGES

Neutrophils are like SUICIDE BOMBERS!

Macrophages continued on next slide


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MACROPHAGES:The largest phagocytic cells Macrophages are amoeboid cells that move through tissue fibers and engulf and digest

cellular debris and pathogens by phagocytosis

They also stimulate lymphocytes and other immune cells to respond to pathogens

A majority of macrophages are stationed at strategic points where microbial invasion is

likely to occur (LIKE A BLOCKADE)

Fixed macrophages are especially numerous in the lymph nodes and in the spleen,

which are key organs of the lymphatic system.


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About 1.5% of the white cells

Their defend against larger parasitic invaders such as worms

Dont attack microorganisms directly

Destroy the bodys own infected cells, especially cells harboring viruses

Also attack cells that could form tumors

The attack is not by phagocytosis but an attack on the membrane of the

target cell

This causes the cell to break open

NATURAL KILLER CELLS


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The most important antimicrobial proteins in the blood and tissues are interferons

and the complement system.

INTERFERONS: proteins secreted by virus-infected cells that inhibit neighboring

cells from making new viruses

COMPLEMENT PROTEINS: involved in nonspecific and specific defense Can lyse a cell target by combining with antibodies

A local inflammatory responseis triggered by tissue damage. Injured cells release

histamine, a chemical signal that dilates blood vessels and increases capillary

permeability allowing large numbers of phagocytic white blood cells to enter the

interstitial fluid.


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The immune system recognizes foreign microbes, toxins or transplanted tissues

It knows that they dont belong

It then develops an immune response to inactivate or destroy the specific type of invader

ANTIGEN: a foreign substance that elicits an immune response

Most antigens are proteins or large polysaccharides

Antigens that trigger an immune response include molecules belonging to viruses,

bacteria, fungi, protozoa, and parasitic worms.

ANTIBODIES: specialized lymphocytes that defend the body against one specific type of antigen.

Antibodies make up a class of proteins called immunoglobulins

An antibody does not usually destroy an antigen directly but targets it for elimination bycomplement or phagocytes


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IMMUNITY

Immunity is the result of the immune systems enhanced response to a previously

encountered pathogen.

ACTIVE IMMUNITY: acquired by exposure to an actual disease or to a vaccine thatsimulates a disease.

PASSIVE IMMUNITY: acquired by administering antibodies formed in others, or it can be

passed from mother to child via the placenta and milk.


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HUMORAL IMMUNITY: based on circulation of antibodies in the blood and lymph, and

defends against free viruses, bacteria, and other extracellular threats.

CELL-MEDIATED IMMUNITY: reacts against transplanted tissue and cancer cells.


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LYMPHOCYTES=MAIN CELLS OF THE IMMUNE SYSTEM

LYMPHOCYTES:

Originate in bone marrow

BLYMPHOCYTES: mature in the bone marrow and function in humoral immunity.

B cells defend against pathogens in body fluids by generating specific

antibodies

T LYMPHOCYTES: mature in the thymus and function mainly in cell-mediated immunity.

T cells defend against intracellular pathogens


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CLONAL SELECTION OF LYMPHOCYTES Is the cellular basis for immunological specificity and diversity

Each lymphocyte recognizes and responds to only one antigen

There is an enormous diversity of antigen-specific lymphocytes. This allows the immune system to defend against an almost unlimited variety of antigens

HOW IT WORKS:

Each lymphocytes specificity for an antigenic target is predetermined during embryonicdevelopment (before an encounter with an antigen ever takes place)

The mark of this specificity is the antigen receptor the lymphocyte bears on its surface

If that antigen enters the body and binds to receptors on the specific lymphocytes, then those

lymphocytes are activated to mount an attack (immune response)

The selected cells go through cell division and develop into a large number of a clone of cells thatcombats the antigen that initiated the response.

CLONE TROOPERSDONT HAVE TO WRITE


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CELL MEMORY OF IMMUNITY

Upon first exposure to an antigen lymphocytes go through PRIMARY IMMUNE RESPONSE

PRIMARY IMMUNE RESPONSE: between initial exposure to an antigen and maximum

production of effector cells, there is a lag period of 5 to 10 days. During this

lag period, the lymphocytes selected by the antigen are differentiating into

effector T cells and antibody-producing plasma cells.

If the body is exposed to the same antigen at some time later, the response is faster (only 3 to

5 days) and more prolonged than the primary response.

SECONDARY IMMUNE RESPONSE: the antibodies produced at this time are also

more effective in binding to the antigen than those produced during the

primary response.

IMMUNOLOGICAL MEMORY: The immune systems ability to recognize an antigen that it already

encountered

IMMUNOLOGICAL MEMORY is possible due to MEMORY CELLS


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MEMORY CELLS

MEMORY CELLS are produced along with the relatively short-lived effector cells of the

primary immune response.

During the primary response, memory cells are inactive

Survive for long periods of time

Multiply rapidly when exposed again to the same antigen that caused their formation

Memory cells are responsible for the usual lifelong immunity of chickenpox after childhood

exposure


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MOLECULAR MARKERS

Molecular markers on cell surfaces function in self/nonself recognition

SELF-TOLERANCE: develops as T and B lymphocytes bearing antigen receptors mature in the

thymus and bone marrow, and continues to develop even as the cells migrate to lymphoidtissues.

Any lymphocytes with receptors for molecules present in the body are destroyed or are made

nonfunctional

This leaves only lymphocytes that are reactive against foreign molecules

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC): a biochemical fingerprint unique to each

individual

2 TYPES OF MHC:

CLASS I MHC: LOCATED ON ALL NUCLEATED CELLS (ALMOST EVERY CELL IN

THE BODY)

CLASS II MHC: RESTRICTED TO A FEW SPECIALIZED CELL TYPES OF THE

BODYS DEFENSE SYSTEM (MACROPHAGES, B CELLS, AND ACTIVATED T

CELLS)

DISEASES CAUSED BY ABNORMALITIES IN IMMUNE FUNCTION


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DISEASES CAUSED BY ABNORMALITIES IN IMMUNE FUNCTION Sometimes the immune system screws up and turns against itself

This can lead to autoimmune diseases such as:

Rheumatoid arthritis

Insulin-dependent diabetesOr in allergies such as:

Hay fever (histamine is released from mast cells by the

allergen pollen)

Some people are naturally deficient in humoral or cell-mediated immune defenses, or both.

AIDS is caused by the destruction of CD4-bearing T cells and other cells by HIV, the

human immunodeficiency virus, over a period of years

AIDS is marked by a low level of helper T cells and


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MUCOUS MEMBR NEM CROPH GES

NTIGENSNTIBODIESMEMORY CELLSMOLECUL R M RKERS


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