Transcript Immune System

Immune System
Means of Defense (3 categories)
First two are Nonspecific
A. Barriers
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Doesn’t distinguish between agents
Helps Prevent Entry into the body
Includes skin and mucous membranes which provide a
mechanical and chemical barrier
Oil and sweat glands give skin an acidic pH which
discourages bacterial growth
Perspiration, tears, and saliva contain an enzyme lysozyme
which breaks down the cell walls of bacteria.
Stomach acid kills bacteria
Nostril hairs-filter out particles and mucous traps
microorganisms. (swept out by cilia)
Means of Defense (3 categories)
B. Nonspecific Internal Defenses
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1. Phagocytic cells like neutrophils and monocytes attack
microorganisms that get through the skin barriers. They engulf
them and consume bacteria, viruses and cell debris in the
interstitial fluid.
Neutrophils make up 60-70% of WBC’s. Short lived.
Monocytes become macrophages which live a long time.
Many wander but some are permanent residents in organs like
the lung or brain
Can engulf 100+ bacteria
2. Natural Killer Cells
Destroy the body’s own infected cells-especially those with
viruses in them
Destroys cells which may be changing and could form tumors
Not phagocytic but lytic-breaks cell membranes.
Means of Defense (3 categories)
3. The Inflammatory Response
Triggered by damage to tissues by injury or microorganisms
Injured cells give off a substance that aids the inflammatory
response
release histamine-which causes dilation of neighboring blood
vessels and makes the capillaries more leaky (histamine is
contained in WBC’s called basophils and in mast cells (in
connective tissue)
Small blood vessels dilate and this increased blood flow causes
the redness, heat and swelling associated with infection. Blood
vessels also become leakier causing swelling due to increased
fluid.
The increased blood flow enhances migration of phagocytic
WBC’s from the blood to the interstitial fluid
neutrophils first
followed by monocytes that develop into macrophages
More Inflammatory Response
Pus- is mostly dead cells and accumulated fluid
(will be absorbed)
Clotting proteins in plasma seal the area off and
prevent the spread of infection.
Systemic Reactions
– the number of WBC’s circulating is increased ( may
be dramatic and within hours)
fever
toxins from the pathogens may trigger fever.
Some WBC’s release pyrogens which set the body
thermostat higher
The higher temperature stimulates phagocytosis and inhibits
the growth of microorganisms and may speed up repair.
Still More Non-specific Response
4. Antimicrobial Proteins- Some proteins attack
microorganisms or negatively affect their reproduction.
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A. Interferon- a substance produced by a virus infected cell
that helps other cells resist the virus
-The virus turns on the interferon gene- can save the infected
cell but diffuses to nearby cells and inhibits viral reproduction
there
-Host specific-not virus specific
-Inteferon may act against cancer since some may be induced
by viruses
one kind mobilizes natural killer cells-destroys tumor cells
may change malignant cell membranes- make them less likely
to metastasize
activates macrophages
Another Antimicrobial Protein
B. Complement
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many (at least 20) proteins that work with other
defense mechanisms
They circulate in the blood in an inactive form
They are activated by the immune response or
markers on microorganisms
They increase the inflammatory responsehistamine release and attraction of phagocytes.
They coat microbes- this increases the rate of
phagocytosis by opsonization (“making tasty”)
They team up to cause lysis of the microbial
membrane
The Third Line of Defense
C. Specific Immune Response
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The immune system learns to distinguish “self” from “non-self”
Detects “antigens”- foreign substances . These cause an increase in
the cells that attack or produce antibodies. They may be things like
molecules on surfaces of viruses and bacteria or marker molecules
on transplanted organs.
The immune response must be activated by the presence of an
antigen
The response is specific for a particular foreign substance or invader
The system remembers the antigens after the initial contact. There is
a quick response the second time. This is memory.
Vaccination- immune response is prevented with a nonvirulent or
weakened form of a pathogen-initiates long term capability to respond
quickly to real infective agent.
-Active immunity- body produces antibodies
-Passive immunity- body acquires antibodies from other sources such
as placenta, injection, immunity is temporary