Download The Immune System

The Immune System
Biology 2201
Unit Three Section Five
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Introduction
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The Immune System provides
specific defenses giving the human
body the ability to fight infection
through the production of antibodies
and cells that attack pathogens.
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Pathogen is any disease producing
organism or virus which can produce
toxins.
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Toxins
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Toxins are substance that interfere with
the normal functioning of our body cells;
(ex.) neurotoxins — attack nerve cells.
The immune system maintains good body
homeostasis by recognizing and
destroying harmful organisms or
substances that may interfere with human
health.
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Examples
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Some examples would be the following :
1) Infectious Diseases : disorders spread
by microorganisms or viruses that can be
transmitted from one person to another.
2) Venereal Diseases : spread by sexual
contact — such as syphilis and gonorrhea
(caused by bacteria) and the AIDS virus.
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Historical Perspective
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Robert Koch (1876) was a German doctor who
discovered a way of identifying pathogens that
caused a particular disease. Disease
Transmission could be by bacteria and viruses.
What Happens :
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1) Pathogens carried by the environment (air ,
water, etc.).
2) Transmitted by direct bodily contact between
an infected person and an uninfected person.
3) Disease can be carried from one human to
another by a third organism; (ex.) malaria.
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Treatment could involve chemotherapy —
use of chemicals such as antibiotics to
treat disease. (ex).
An antibiotic can be a bacteria-killing
substance produced in living things; such
as penicillin (first discovered by Alexander
Fleming in 1928).
Remember that an antibiotic can kill
bacteria, but not a virus.
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Immunity
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Immunity is the ability of the body to resist
a disease. The immune system is very
active in the process of immunity and the
body’s immune response.
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Non-specific immunity
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Where prior exposure is not necessary for
it to be effective.
Non-specific immunity includes:
Physical barriers (1st line of defense) such as
the skin, mucous membranes, sweat, saliva,
gastric juices and tears.
 Phagocytic cells (2nd line of defense) such as
Macrophages, Neutrophils, and Monocytes.
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Non-specific Defenses
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Phagocytosis is the process by which a cell ingests
bacteria to destroy them. Some ways the body
counteracts pathogens are the following:
1) Macrophages : phagocytic cells produced in bone
marrow. They are found in the liver, spleen, brain and
lungs and also circulate in the bloodstream and
interstitial fluid. They protect body against a wide range
of pathogens (disease causing agents);
2) Neutrophils are leucocytes or WBC’s that engulf
bacteria through phagocytosis.
3) Monocytes are the WBC’s from which neutrophils
and macrophages are derived.
4) Natural killer cells are WBC’s that carry out
phagocytosis on cancerous body cells or body cells
infected by viruses.
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Caption:-- Alveolar macrophage phagocytosis of E. coli on the outer surface of a blood vessel
(lung pleural cavity).
File Name:-- 8957B
Category:-- Medical Type of Image:-- SEM
Magnification:-- x1,315--(Based on an image size of 1 inch in the narrow dimension)
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Specific Immunity
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The lymphocytes are specialized white
blood cells (WBC’s) produced in bone
marrow.
They are the primary structures of the
specific immune system that protect the
body against a wide variety of infections.
They are divided into two groups,
depending on where they mature :
i) B lymphocytes (B cells) mature in bone
marrow and
 ii) T lymphocytes (T cells) mature in the
thymus gland.
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Immune Response
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1. An immune response is the reaction of the
immune system to the presence of foreign cells
or molecules. .
It causes the production of antibodies and
specialized cells that bind to and inactivate
foreign substances.
This immune response is an antigen / antibody
reaction. An antigen is any substance that
causes an immune response — (ex.) viruses ,
microorganisms ; (most antigens are proteins,
but some can be CHO or nucleic acids).
An antibody is a protein in the blood that binds
to and helps destroy foreign substances in the
body; (it is a y-shaped molecule that attaches to
an antigen).
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2. Complete Immune Response
First-Line Defense — Physical and Chemical Barriers:
 The body's first line of defense against pathogens
involves several kinds of physical and chemical barriers.
 These include skin, sweat, tear, saliva, membranes lining
body passages, mucus, stomach acid, and urine.
 Unbroken skin and the membranes lining the body
passages are effective barriers to most pathogens.
 Sweat, tears and saliva contain chemicals that kill or
inhabit some bacteria.
 Mucus that covers internal membranes entraps
pathogens that are then washed away or destroyed by
chemicals.
 Stomach acid destroys many pathogens that may be
present in food.
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Second-Line Defense — Inflammatory
Response :
 If a pathogen gets past the first line on
defense and starts and infection, parts of
the second line of defense become
activated.
 This results in the inflammatory response, a
reaction of the body that causes swelling,
redness, warmth, and pain in the area of
infection. Cells that are damaged from the
infection release certain chemicals called
histamines.
 These chemicals causes blood vessels to
dilate and become more permeable to fluid
and leucocytes.
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This increased blood flow and accumulation of
fluid causes swelling and warmth in the affected
area.
This attracts phagocytic macrophages that
ingest and destroy large numbers of bacteria.
As the inflammatory response proceeds, the
phagocytes ingest the pathogens and any
damaged tissue.
Eventually pus, a mixture of phagocytes, dead
cells, bacteria, and body fluid, collects in the
wound.
The pus either drains or is absorbed by the
body. Most of the time, the pathogen is
destroyed, the inflammation dies down, and the
wound heals.
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Infected area (swelling, redness etc.)
INFLAMMATION
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Damaged cells (release certain chemicals
called Histamines which cause increased
blood flow to the damaged area by
increasing the diameter of the capillaries)
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Attracts Phagocytes (neutrophils and
macrophages) — (WBC's that ingest large
numbers of bacteria).
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Third Line of Defense — The Immune
Response :
 This line of defense begins after the pathogen
has been destroyed and the antigens from the
pathogen protrude from a macrophage.
 These antigens or foreign materials are easily
detected as having genetic markers that differ
from those of our own body.
 After a macrophage displays an antigen on it's
surface, helper T cells bind to the antigens on
the surface of the antigen.
 This triggers chemical messengers to be
released to cause the T cells to multiply in
number.
 Some of the T cells can disrupt the reproductive
cycle of the pathogen by destroying infected
tissue cells.
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The antibodies on B cells can bind to the antigens,
thus helping to destroy the pathogens.
The T cells and the B cell antigen-antibody complex
combine.
This union of T and B cells will activate the B cells.
Activated B cells will enlarge and divide producing
memory B cells and plasma cells.
The plasma cells will produce the antibodies (at a
rate of 2000 per second) to be released into the
bloodstream to fight invading pathogens.
After the infection has been fought off, the memory
T cells remain in the blood ready to fight off a new
infection by the same pathogen.
If the same antigen is found again in the
bloodstream, the response time will be much faster
with higher levels of antibodies.
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Acquired Immunity
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Immunity can be acquired in two ways:
naturally through infection or passive
transfer, and artificially by medical
treatments.
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Passive Immunity
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This type of immunity is acquired when a
doctor gives you an injection or serum;
(ie.) receive antibodies from another
person.
This serum contains certain anti-bodies for
fighting a particular disease and is
obtained by taking a sample of blood from
a person or animal who has recovered
from the disease or has been immunized
against it.
Instead of using the entire serum, the
doctors use part of it that contains most of
the anti-bodies.
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Doctors can give this to people to protect
them against such diseases as measles or
viral hepatitis.
Passive immunity can also occur during
pregnancy.
Antibodies from the mother can pass
through the placental barrier and give the
newborn short-term passive immunity to
some diseases.
These antibodies are also present in
breast milk and can prolong passive
immunity.
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Active Immunity
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This type of immunity is acquired after a
certain antigen enters the body through an
infection or vaccination.
Memory B cells and T cells will react to a
later attack by the same antigen much
more quickly than the first time around
because the cells store information about
the antigen and know how to better
destroy it.
The killer T cells' attack will be stronger
and last longer the second time around.
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Autoimmune Disorders
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An autoimmune disease is a condition in which the body’s
own T cells or antibodies attacking body tissues as foreign
antigens.
The actual cause of this disease is unknown and there is a
tendency for such diseases to be inherited.
MS (multiple sclerosis) is a condition which affects the
myelin covering of nerve fibers.
Rheumatoid arthritis is a chronic autoimmune disease that
affects the bone and tissue of joints in the body.
It is characterized by inflammation of the lining of the joints.
What happens is that the body’s own immune system attacks
the joints causing pain, stiffness and swelling to occur.
It is a crippling form of arthritis that can affect anyone but is
most common in individuals between the ages of 25 and 50.
Treatment can involve drugs such as aspirin, NSAIDs (nonsteroidal anti-inflammatory drugs and steroids.
More severe cases can involve using DMARDs (diseasemodifying antirheumatic drugs) and corticosteroids.
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An Allergic Reaction
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Allergies are due to another type of immune malfunction.
It is an exaggerated response by the immune system to
such allergens as pollen, mould or cat dander.
Allergic reactions to food or to inhaled allergens (as in
asthma) are also possible.
An allergic reaction may be immediate or delayed with
the immediate or acute reaction being the most common
type. An immediate reaction can occur within 30 seconds
and last up to 30 minutes.
What happens is that an allergen causes specialized
antibodies to trigger certain cells to release histamines.
The histamines cause the permeability of blood vessels
to increase, making the area red or swollen
It can also cause the release of cellular fluids, resulting
in watery eyes and a runny nose.
This is your allergic reaction.
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