Download defense-against-infectious-diseases-6-3-2015

Defense Against Infectious Diseases
6.3
6.3
• Pathogens
– An organism or
virus that causes a
disease
– Viruses, bacteria,
fungi, protozoa,
flatworms, and
roundworms can all
be pathogens
– Examples include:
• Viruses – Rhinovirus (causes the
common cold), HIV, HCB (Hepatitis B
virus)
• Bacteria – Staphylococcus (causes
strep throat), Vibrio Cholerae (causes
cholera), Myobacterium tuberculosis
(causes TB)
• Fungi – Candida (yeast infections),
Trichophyton (fungus that causes
ringworm)
The Common Cold
– Methods of transmission
• Cuts in the skin
• Mouth, Nose, and Eyes
• Vectors (animals that transmit
disease)
• Sexual Transmission
• IV Drug Use
• Blood Transfusions
• Food and Water
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• Barriers to infections
– First line of defense: prevent pathogens from
entering the blood stream
• Skin
–The skin is a tough, impenetrable
physical barrier
–Skin has a lower pH which make it
inhospitable for many bacteria
–Sweat has lysozymes (special enzymes)
that destroy bacteria
When Skin is Broken
• When the skin is broken we lose the primary
line of defense for our body.
• Cuts in the skin are sealed by blood clotting
• Clotting factors are released from the platelets
in the blood.
• Thrombin –
Hormone that triggers
a cascade of reactions
that convert fibrogen
to fibrin.
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• Mucous membranes
–Traps pathogens because it is sticky
–Cilia in the throat sweep up bacteria and
allow them to be swallowed and then
destroyed by acid in the stomach
–Contains
phagocytes
(white blood
cells that
ingest and
destroy
pathogens)
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macrophage
Phagocyte
(large)
neutrophil
Leucocyte (white
blood cell)
T-cell
Lymphocyte
(small)
B-Cell
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• Cellular Defense
– Second line of defense is the non-specific
immune system - a host of quick, non-specific
methods of killing microbes that have entered
the body.
• Leucocytes = general category of white
blood cells
• Phagocytes: large,
irregularly-shaped
leukocyte cells that
remove bacteria,
viruses, cellular
debris and dust
particles.
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• Are constantly changing shape, and they
flow over pathogens, surrounding and
ingesting them through the process of
phagocytosis to form a phagosome
• Enzymes within the lysosome of the
phagosome break down the pathogen
• Different phagocyte cells work in different
locations:
– neutrophils circulate in the blood
– macrophages are found in lymph, tissue fluid,
lungs and other spaces, where they kill
microbes before they enter the blood
6.3
• https://www.youtube.com/watch?v=CEOVSFTlpY
Now that you have gotten infected
• Antibiotics
– Work on bacteria, not viruses
• Antibiotics block specific metabolic
pathways found in bacteria, but not in
eukaryotic cells (such as our own)
– Examples: RNA replication, transcription, translation, 70S
ribosome function and cell wall formation
• Since viruses do not metabolize on
their own (they use our cell’s
metabolic machinery) they are not
effected by the antibiotics
• Antibiotics: Types
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– _____-static: (bacteriostatic, fungistatic) stop
further growth but don’t kill existing microbes.
• Buys time for immune system to catch up and target
microbes.
– _____-cidal: (bacteriocidal, fungicidal) kills
microbes
– Antibiotic resistance
• Some bacteria develop a gene mutation that
makes them naturally resistant to antibiotics
• Resistance can be transferred from strain to
strain and sometimes from species to
species
• Bacteria that have a resistance mutation
survive when antibiotics are used and other
bacterium die
• Resistant bacteria pass on their genes for
resistance to offspring
• Proportion of resistant bacteria increases in
each generation
• This is an excellent example of natural
selection and evolution
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• Antigen and Antibodies
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• Antigen and Antibodies
– Antigens
• Large molecules on the outer surface of cells
• All living cells as well as viruses have antigens
• All cells in one organism will have the same type of
antigen (which is genetically controlled)
• Therefore, the antigen acts as identification marker
for cells
• If a pathogen enters the body the immune system
will detect the foreign antigen and begin to attack
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– Antibodies (also called immunoglobulin)
• Proteins that bind to the specific antigen on a
pathogen to help to destroy it
• Each has a variable region that is antigen specific
(similar to enzyme specificity)
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Youtube.com
Specific Immunity: Antibodies
https://www.youtube.com/watch?v=Ys_V6FcYD5
I
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– Antibody production
• Many types of b-cells exist
• Each type recognizes one specific antigen
and responds by dividing to form a clone
• This clone then secretes numerous copies of
a specific antibody against the antigen
• Cloning and antibody production is always
initiated by the binding of a t-cell (another
type of white blood cell) to the b-cell
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6.3
• HIV and Aids
– HIV, or Human
Immunodeficiency Virus,
was first noticed by the
CDC (center for disease
control) in 1981
– The U.S. origin of the
disease was traced back
to “patient zero”, a french
flight attendant who slept
with hundreds of men
throughout the country
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• HIV and AIDS
– HIV can remain hidden in the body for years
– It survives by invading and killing T-Cells
– When enough T-cells have been destroyed, the
immune system begins to fail and AIDS, or Acquired
Immune Deficiency Syndrome, has begun
– Aids patients do not die from the virus itself, but rather
from the diseases that take hold of the body in the
absence of a proper immune system
– Many anti-viral drugs are now available for AIDS
patients
Effect of HIV on Immune System
• The HIV virus limits the number of active
lymphocytes in an organism
– This makes it much harder for the organism to
fight off possible infectious pathogens
• Lose the ability to produce antibodies
– Leads to the development of AIDS
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• The drugs usually do not work alone, however,
and must be administered in combinations
called “cocktails”
• The drugs do not destroy the virus completely,
but rather slow down the rate of replication
• After a few years, the drugs tend to lose their
affect and the patient must begin a new drug
regime
• Sides effects of the drugs can be horrible and
include hallucinations, insomnia, and severe
depression
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– HIV is transmitted through vaginal fluid,
semen, blood, and sometimes breast milk
– Sexual contact and IV drug use (sharing of dirty
needles) are the most common ways that
these bodily fluids are passed from person to
person
– The social implications of AIDS are numerous
and devastating, especially in southern Africa
where the number of cases is disproportionate
to other areas of the world
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• As a result of the large numbers of people with
the disease and no health care in these nations
there are many orphaned children
• Having AIDS or having family members with the
disease also provides a social stigma that may
make it hard to get a job
• Having AIDS may also make it hard to obtain
health insurance