Transcript THE IMMUNE SYSTEM DEFENSES AGAINST INFECTION Pathogens

THE IMMUNE SYSTEM
DEFENSES AGAINST INFECTION
Pathogens: Viruses, bacteria, and other
microorganisms that cause disease.
Pathogens are present everywhere in the
environment
In the food you eat
In the water you drink
In the air you breath.
YOUR BODY HAS SEVERAL EFFECTIVE
DEFENSES AGAINST PATHOGENS
The immune system carries out a major part of the
protective function of blood.
Cells of the immune system are on constant patrol, ready
to attack foreign invaders that get past other body
defenses.
The immune system is not the only infection fighting
system of the body, but it is the most complex.
There are basically three lines of defense against disease
causing organisms.
FIRST LINE OF DEFENSE
Involves several kinds of physical and chemical barriers
These include: skin, sweat, tears, saliva, membranes lining
body passages, mucus, stomach acid, and urine.
Unbroken skin, and membranes lining body passages are
effective barriers to most pathogens
Sweat, tears, and saliva contain chemicals that kill or
inhibit some kinds of bacteria
Mucus traps pathogens that are then washed away or
destroyed by chemicals
SECOND LINE DEFENSES
If pathogens get past the First Line barriers, an inflammatory
response results.
An inflammatory response is a reaction of the body that causes
swelling, redness, warmth, and pain in the area of infection.
Cells damaged by the infection release chemicals that increase blood
flow to the area.
Increased blood flow causes puffiness and warmth and attracts
macrophages to the area.
A macrophage is a large white blood cell that can ingest large
numbers of bacteria.
SECOND LINE DEFENSES
Macrophages ingest the pathogens and any damaged
tissue.
Eventually pus: a mixture of macrophages, dead cells,
bacteria, and body fluids collects in the wound.
Pus is then absorbed by the body or drained, the pathogen
is destroyed, the inflammation dies down and the wound
is healed.
If the pathogen is a virus, healthy cells surrounding the
infection produce an enzyme that blocks the
reproduction of the virus.
THIRD LINE DEFENSES
If the infection is not stopped by the inflammatory
response, the pathogen is targeted for destruction
by the last line of defense – the immune system.
The immune system recognizes, attacks, destroys,
and “remembers” each kind of pathogen or
foreign substance that enters the body.
This is done by producing antibodies and
specialized cells that bind to and inactivate
pathogens.
THIRD LINE DEFENSES
Antibodies: Proteins in the blood that bind to help
destroy pathogens in the blood. Mark the pathogen
for death.
Unlike the First and Second Lines of Defense, the Third
Line can tell the difference between different types of
pathogens.
For each type of pathogen, the immune system
produces antibodies or cells that are specific to that
pathogen.
THE IMMUNE RESPONSE
The immune system includes all parts of the body
that are involved in the recognition and
destruction of foreign materials.
Bone marrow – produces white blood cells
White blood cells – especially phagocytes and
lymphocytes
Tissues of the lymphatic system: lymph nodes,
tonsils, spleen (these produce white blood cells
called lymphocytes).
WHICH CELLS ARE FRIENDS
AND WHICH ARE FOES?
For the immune system to work the body needs to the
difference between itself (own cells and materials) and
nonself (foreign cells and materials)
This recognition is based on differences in certain large
molecules (proteins) between one organism and another.
When the body recognizes that a cell is a foreign invader it
produces antibodies or special cells that bind to
inactivate the invader and/or target it for destruction.
THE IMMUNE RESPONSE
The production of antibodies and specialized cells that bind
to and inactivate foreign substances is called the
immune response.
Antigen: Any substance that can cause an immune
response.
Viruses and bacteria have substances on their outer
surfaces that are antigens that stimulate an immune
response.
Antigens are usually proteins, but carbohydrates and
nucleic acids may also be antigens.
ANTIGENS AND TRANSPLANTS
The cells of each human contain a unique combination of
antigens that no other human has.
As a result tissue from one person transplanted to another
will act as an antigen and trigger an immune response.
An immune response to an antigen acts to destroy the
antigen.
That is why blood transfusions and organ transplants
require the antigens to match as much as possible.
Otherwise the body will attack the new tissue.
KEEPING ALL THE TERMS
STRAIGHT.
Some of the terms sound similar and may be confusing.
Pathogen: a disease causing microorganism
Antigen: a substance on the outer surface of a
microorganism (a pathogen or foreign invader) that
triggers an immune response.
Antibody: Proteins in the blood that bind to and
inactivate and/or target a cell for destruction.