Download THE IMMUNE STYSTEM

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THE IMMUNE STYSTEM
The Immune System
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The body must defend itself against potentially
dangerous viruses, bacteria and other pathogens. It
must also contend with abnormal cells and cell that
may develop into cancer.
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HIV
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Cancer cells in
bone marrow
The Immune System
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There are two types of defense that the body has
to fight these threats.
 Innate
Immunity – a defense that is present from birth.
Usually nonspecific responding to a broad range of
microbes. Consists of external and internal barriers,
phagocytic white blood cells called macrophages.
 Acquired Immunity – also called adaptive immunity.
Developes only after exposure to microbes, abnormal
body cells, and toxins. Highly specific. White blood
cells called lymphocytes are involved as well as
proteins called antibodies.
Overview of defenses against bacteria viruses
and other pathogens
INNATE IMMUNITY
Rapid Responses to a
broad range of microbes
External defenses
Internal defenses
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Skin
Mucous membranes
Secretions
1st line of defense
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Flu Virus
Phagocytic Cells
Antimicrobial proteins
Inflammatory Response
Natural Killer Cells
2nd line of defense
ACQUIRED IMMUNITY
Slower responses to
specific microbes
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Humoral Response
(antibodies)
Cell Mediated response
(Cytotoxic lymphocytes)
3rd line of defense
External Defenses:
These are the first line of defense from diseases
Skin
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is impenetrable to viruses
or bacteria.
Tiny cuts may allow
penetration of pathogens.
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Mucous membranes
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line the respiratory, digestive and genitouterary
tracts block entry of pathogens. Cells of these
membranes produce mucus which traps microbes.
Ex: The trachea has ciliated
epithelial cells that
sweep mucus and any trapped
debris upward away from the
lungs.
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Secretions
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Saliva, tears - wash away surfaces of epithelial cells.
Sebaceous (Oil) glands and sweat glands - give the skin
a pH ranging from 3 -5 which is acidic enough to
prevent the colonization of some microbes
Lysozyme – an enzyme contained in secretions from the
skin that digests the cell walls of many bacteria
(peptidoglycan)
Gastric Juices – acidic pH kills pathogens before they
reach the intestines.
Exception: Hepatitis A virus can survive gastric acidity
Internal Defenses –
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nd
2
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microbes that get past the external defenses must
then contend with the internal mechanisms of innate
defense.
Phagocytic Cells
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phagocytosis is the ingestion of invading
microorganisms by a certain type of wbc called
phagocytes.
Phagocyte and
gonococci
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Attach to their prey by way of surface receptors
that bind to structures found on many microbes but
not on regular body cells. An example of this
structure is polysaccharides found on the surface of
bacteria.
Engulfs the microbe(s) then forms a vacuole.
Vacuole fuses with a lysosome
Nitric oxide and other toxins poison the microbes
Enzymes breakdown the molecules that make up the
microbe
4 Types of White Blood Cells (leukocytes) that
are phagocytic:
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Neutrophils
 Enter
infected tissue and engulf microbes about 70%
of wbc’s. Self destruct in a few days
Macrophages
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“the
big eater” large
phagocytes that
engulf microbes and
dead tissue cells. Live
longer than neutrophils
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Eosinophils
 Attack
large parasites
with enzymes (blood fluke)
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Dendritic Cells
 Ingest
microbes like macrophages and stimulates
acquired immunity
Antimicrobial proteins – proteins that become
activated and secreted when there is an infection.
 Examples include lactoferrin binds iron which is
necessary for bacteria to grow and defensins
which kill fungi
bacteria and viruses
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Complement System - a group of proteins that lead
to the lyses (bursting) of invading microbes.
 Substances
on the surface of microbes activate the
complement system.
Interferons
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Limit the spread of viruses by keeping them from
replicating.
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Inflammatory Response
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Damage to tissue by physical injury or entry of
pthogens leads to the release of chemical signals
that trigger a response.
Histamine - a chemical stored in mast cells found in
connective tissues. Histamine dilates capillaries and
increases their permeability
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Chemokines are small proteins that guide
phagocytes to the site of injury
Macrophages release chemicals like prostoglandins
that promote blood flow to the site of injury
Result is inflammation, redness, swelling.
Natural Killer Cells
NK cells patrol the body and attack viral infected
cells and cancer cells
 Once attached to an infected cell, it releases
chemicals that cause the cell to undergo apoptosis
(programmed cell death)
 NK cells are not 100%
effective.
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