Transcript Topic 6.3 Defensex

Defense Against
Infectious Disease
Topic 6.3
Types of Pathogens
Cause
Disease
Virus
influenza, polio, mumps, measles
Bacteria
pneumonia, strept throat, syphilis,
cholera, whooping cough
Fungi
athlete's foot, ringworm
yeast infection
Protozoan
amoebic dysentery,
sleeping sickness, malaria
Pathogens
Barriers to Infection
• Pathogens are organisms or viruses that cause
a disease.
• The skin and mucous membranes form a
barrier that prevent most pathogens from
ever entering the body. (primary response)
The Skin
• Outer layer of skin is tough and forms the first layer of
defense (primary response). Dry skin also inhibits bacterial
growths.
• Sebaceous glands in the skin secrete lactic acid and fatty acids
which make the surface of the skin acidic preventing bacteria
growth.
• Fatty acids and waxes have antimicrobial properties
• Bacteria on the skin as well as in the mucous membranes
prevent other bacteria from growing
• lysozymes in sweat and saliva (mucous membranes) keep
bacterial growth in check
Mucous Membranes
• Mucous membranes are soft areas of the skin
that are kept moist with mucus.
• Mucous traps bacteria in sticky mucus that is
slightly acidic. (vagina, nasal passages,
trachea, urethra)
• Cilia sweeps mucous up to be swallowed to kill
bacteria.
• Contain macrophages and phagocytes that
destroy pathogens. (primary response)
Blood Clotting
• A blood clot is the response of the body to seal up
wounds to prevent passage of pathogens.
• Platelets that are responsible for blood clotting are
constantly circulating within the blood among
erythrocytes and leukocytes.
• Clotting process begins with the release of clotting
factor from either damaged tissue or platelets.
Blood Clotting
• Clotting factors form a
series of reactions where
the product of one step is
the substrate of the next.
• This prevents clotting
from happening
spontaneously.
• Enzyme thrombin
converts soluble
fibrinogen to insoluble
fibrin
Macrophages (phagocytes)
• Macrophages make up some of the leukocytes within
the blood.
• Macrophages engulf pathogens and ingest them by
phagocytosis (endocytosis).
• Macrophages are able to move from blood capillaries
towards certain tissues to sites of infection.
• Large numbers of Macrophages at a site of infection
forms pus.
• This type of response is referred to as non-specific/first
line of defense response.
• The macrophage only identifies the pathogen as “notself” and eliminates it.
Antibodies and Antigens
• Foreign antigens are proteins found on cell walls of
pathogenic bacteria or fungi and protein coats of
viruses (most organisms have antigens)
• Different pathogens may have several different types
of antigens on the surface of their cell membrane
• Antibodies are proteins made by the immune system
that recognize and bind to foreign antigens on
pathogens
• Each antibody only binds to one type of antigen.
Antigen-Antibody
Antigen-Antibody
Developing Natural (True) Immunity
• Antibodies are made by lymphocytes called Bcells.
• There are over 1015 types of antibodies.
• Few B-cells exist at one time.
• B-cells will produce antibodies if they encounter
an antigen that their antibody binds to.
• If an antigen is found they then multiply and
produce many clone cells.
• Antibody production by B-cells usually depends
on the help of other types of lymphocytes
including macrophages and helper T-cells.
Types of Immunity
• Passive: acquiring antibodies that were produced in
another organism.
– Example: breast milk, placenta-fetus, antibiotics.
• Active:
– Leads to the production of memory cells. Antibodies are
produced by the infected organism.
– Example: vaccines, overcoming a sickness
• Natural
– Acquiring immunity through contraction of a disease or illness
• Artificial:
– Acquiring immunity through methods other than your own
immune system.
Antibiotic use
• Antibiotics work on prokaryotes (bacteria)
only. Inhibits DNA replication, cell wall
formation, protein synthesis
• Humans are eukaryotic so our cells are not
affected
• Viruses “hide” inside our eukaryotic cells so
antibiotics are ineffective on them as well.
Development of Penicillin
• Penicillin is produced by fungi.
• Fungi compete with bacteria for food
• Penicillin is made in fungi when food is scare
and competition is increased
• Discovered by Alexander Fleming in 1928
• Florey and Chain figured out how to get fungi
to continuously produce penicillin and then
tested it on mice…and then humans
Development of Penicillin
Antibiotic resistance
• Some strains of bacteria have developed a
resistance to antibiotics.
• Already had a gene that promoted resistance
• Kills off all non-resistant bacteria which means
less competition for them!
• Must only take antibiotics when needed and
complete the entire course of antibiotics
• Farmers should reduce the use of antibiotics
in farming
AIDS
(Acquired Immunodeficiency Syndrome)
• AIDS is an example of a syndrome (a group of
symptoms that are found together).
• Individuals with AIDS have low numbers of
lymphocytes as well as weight loss and usually
a variety of other diseases caused by viruses,
bacteria, fungi, and protozoa which eventually
lead to death.
Cause of AIDS
• HIV (human immunodeficiency virus) causes AIDS.
• The virus infects a type of lymphocyte (t-cells) that
plays a vital role in antibody production.
• Over a period of years these lymphocytes are
destroyed and antibodies can no longer be produced.
• Without the production of antibodies the body is
susceptible to pathogens that normally wouldn’t
harm you.
Transmission of AIDS
• Blood Transfusions
• Mother to child :
– Across the placenta from a mother to a baby
– Through cuts from child birth
– In milk during breast feeding
• Blood on hypodermic needles that is shared
by intravenous drug users
• Through small cuts or tears from vaginal, anal
or oral sex.