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Disease- any change, other than an injury,
that disrupts the normal functions of the
body
Pathogens- disease-causing agents
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Bacteria
Viruses
Fungi
Environmental agents
Inherited agents
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Viruses- tiny particles that invade and
replicate within living cells
◦ Take over many of the functions of the host cell
◦ Common cold, influenza, smallpox, and warts
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Bacteria- single-celled organism that lacks
a nucleus
◦ Some are harmless to humans
◦ Cause diseases by breaking down the tissues of
the infected organisms from food or by releasing
toxins that harm the body
◦ Streptococcus infections, diphtheria, botulism,
and anthrax
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Protists- eukaryote that is not a plant, animal
or fungus
◦ Malaria- caused by Plasmodium spread by
mosquitos
◦ African sleeping sickness- caused by Trypanosoma,
which lives in the bloodstreams of vertebrate
animals
◦ Amebic dysentery- caused by Entamoeba, located
in contaminated water supplies
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Worms- flatworms, roundworms, tapeworms,
and hookworms
◦ Schistosoma- a flatworm infecting people working
in rice fields
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Fungi-obtain energy from dead, organic
matter
◦ Tinea- athlete’s foot and ringworm
◦ Others can infect the mouth, throat, fingernails, and
toenails
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First line of defense
◦ Skin- most important barrier
◦ mucus- lines nose and throat and helps to trap
pathogens
◦ Oil and sweat glands- produce an acidic
environment that kills many bacteria
◦ Tears- protect eye openings
◦ Saliva- protects mouth opening
◦ Cilia- line nose and throat and help to push
pathogens away from lungs
◦ Stomach acid and digestive enzymes- destroy
many pathogens that make their way to your
stomach
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2nd line of defense
◦ Inflammatory response- a nonspecific defense
reaction to tissue damage caused by injury or
infection
 White blood cells multiply; blood vessels expand;
phagocytes (WBC) engulf and destroy bacteria
 Fever- elevated body temperature
 Important because many pathogens can survive only within a
narrow temperature range
◦ Interferon- proteins that help other cells resist
viral infections
 Function: inhibit the synthesis of viral proteins in infected
cells and help block viral replication
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Includes lumph nodes and lymph fluid.
Lymph fluid is blood plasma (liquid that
makes up the blood minus the red and white
cells). Bacteria or other pathogens that enter
the body find their way into this fluid, which
is filtered through the lymph nodes. The
lymph nodes then filter the fluid and remove
these dangerous particles. These lymph
nodes may swell when fighting an infection,
hence you can feel those bulges at your neck
when you're sick.
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The Thymus - this organ lays between your
breastbone and your heart. It is responsible for
making T-cells.
Spleen - filters blood and removes any foreign
particles and old blood cells in need of
replacement. A person missing a spleen may get
sick more often than one without a spleen
Bone Marrow - produces new blood cells, both
red and white. The bone marrow produces all
blood cells from STEM CELLS, which mature into
different types of white blood cells.
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White Blood Cells - also known as Leukocytes
◦ Neutrophil - suicide bomber cells that destroy cells
infected by a virus
◦ Macrophages - consume pathogens
◦ B Cells - mature into plasma cells when stimulated
◦ Plasma Cells - produce antibodies specific to an
invader
◦ Cytotoxic (Killer) T Cells - bump into infected cells,
poke holes in them and destroy them
◦ Helper T Cells - activate Killer T cells and B cells
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collectively called phagocytes -- converge on
the invaders and proceed to literally "eat
them up." Generally the phagocytes will build
up in one place, causing what we call puss -in order to eliminate the waste.
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Antigens are substances that trigger an
immune response. Cells infected by viruses
displace antigens on their surfaces. These
antigens are recognized by other cells.
Antibodies are the bodies best defense
against viruses. However, antibodies are
specific in their actions, that is that a
chickenpox antibody will only attack a
chickenpox virus. Thus a particular virus
stimulates the production of a particular
antibody.