What Causes Disease?
• Germ Theory of Disease:
– Developed by Louis Pasteur and Robert Koch
• Infectious diseases occur when
microorganisms cause changes that
disrupt normal body functions
What Causes Infectious Disease?
Pathogens:
– disease producing agents that are foreign to
the host
– Ex: Bacteria, protozoa, fungi, viruses,
microbes
How are Diseases Transmitted?
• Direct contact/exchange of bodily fluids:
– kissing, sexual intercourse
• Contact with Object:
– contaminated surfaces, needles
• Air-bourne:
– sneezing, coughing
• Contaminated Water or Food
• Animal Vector: (carries disease but is not sick)
– Ex: mosquitos (malaria) fleas (plague), ticks (lyme disease)
• Flu Attack: How a virus invades your body
• http://www.youtube.com/watch?v=Rpj0em
EGShQ&safe=active
Defense Against Infection
• Physical and Chemical Barriers:
– Skin
– Saliva, mucous and tears
• all contain lysosome, an enzyme that breaks down
bacterial walls
– Stomach acids
– Cilia
Defense Against Infection
• Inflammatory response
– Antigens trigger release of histamines from certain cells
– Histamines increase blood flow to the infected area
bringing more WBCs
– Area gets hot, red and painful
• Fever:
– chemicals are released that increase body temp which
can stop or slow growth of some pathogens and can
speed up immune response
The Immune Response
• Function of the transport system
• Reaction of body to foreign organism or
substances not normally present in the
body (antigens)
Specific Defenses
• Body must distinguish between “self” and “nonself” and inactivate or kill any foreign substance
or cell that enters the body
• Immune defenses are triggered by antigens
typically located on the outer surface of bacteria,
viruses or parasites
• Responds by increasing the number of cells that
attack invaders or produce antibodies.
• Antibodies
– “tag” antigens for destruction by immune cells
• May be attached to certain WBC
• May be free floating in blood plasma
– The shape of each type of antibody allows it
to bind to one specific antigen
The Role of WBCs
• Phagocytic WBC: ingest and destroy
pathogens
– Called macrophages, they engulf and destroy
cells and bacteria
• Lymphocytes:
– WBCs that produce specific antibodies that
neutralize antigens
•
http://www.youtube.com/watch?v=lrYlZJiuf18&list=PL2165FA6A0E3DDF85&safe=active
Immune Response (Read Only)
• Bacteria invade and are engulfed by macrophages
• Macrophage takes portion of bacteria and positions it in its cell
membrane as antigens
• Special WBC called helper T-cells bind to these antigens and become
‘activated”
• The T-cells then bind to B-cells causing them to divide and produce
plasma cells and memory B cells
• Plasma cells secrete antibodies
• Memory B cells and antibodies stay in the bloodstream and attack
and mark the antigens quickly for destruction by macrophages the
next time they enter the body
• Antibodies recognize the antigens to which it should bind
• Form an antibody-antigen complex
• http://www.youtube.com/watch?v=Ys_V6FcYD5I&list=PL2165FA6A0
E3DDF85&safe=active
Fighting Infectious Disease
Active Immunity
– From natural exposure to antigen
• fighting an infection
– From deliberate exposure to antigen
• vaccination
• How does Active Immunity Work?
– You are exposed to an antigen
– Body actively creates antibodies to fight it
– WBCs recognize foreign substance (antigen)
and develop specific antibodies to it
– Immunity lasts a long time
Why Don’t I Get Chicken Pox Twice?
– Once you fight off an infection, your body produces
“memory cells”
– These cells stick around in blood and react quickly if
exposure to that particular antigen happens again
– Person won’t develop the full blown disease again
• What happens when you get Vaccinated?
Smallpox and Vaccine
Development
Jenner, Smallpox and the Development of
the First Vaccine:
http://www.youtube.com/watch?v=qdrpujS
HfsU&safe=active
What is in a vaccine?
• Dead or weakened
version of the pathogen.
– Not enough to cause a full
blown disease
• Stimulates lymphocytes
to develops antibodies
specific to that antigen
• Vaccines:
http://www.youtube.com/watch?v=A
9HUN5kKK4A&safe=active
• “Memory” cells
remember this antigen
so antibodies can be
produced quickly next
time you are infected
• If ever exposed to
antigen in the future
your body will be able
to fight it off quickly
• Helps develop “active”
immunity
• How Vaccines Work
• http://www.youtube.com/watch?v=k3CWx
ekGt7Y&safe=active
• Why do I have to get a Flu Shot every year?
– There are many variants of the virus that causes Flu
• Antibodies are specific to only one antigen
– Virus can undergo mutations that make it resistant to
certain antibodies that might have been effective in
the past
•
•
The Flu Shot:
http://www.youtube.com/watch?v=5q8RNbeJTmI&safe=active
Passive Immunity
– Person given antibodies
they don’t make
themselves
– They are not exposed directly
to the antigen
– Immunity lasts only a short
time
– Ex:
• Passed from pregnant woman
to fetus (across placenta) or to
baby through breast milk
• Injected directly (ex: antibodies
for rabies)
Immune System Disorders
• Allergies
– Body responds to a harmless antigen (like pollen,
peanuts)
– Often produces an elevated inflammatory response.
– Not everyone has the same sensitivity to the antigen
• Autoimmune Diseases
– Bodies immune system attacks your own cells
AIDS
– AIDS is caused by the human immunodeficiency virus
(HIV).
– This virus weakens the immune system and the
person is unable to fight off infections
T cells involved in immune
response get killed.
– Victim vulnerable to many serious diseases,
such as tuberculosis, pneumonia, fungal
infections, and cancer.
– Death usually occurs as a result of one of these
diseases.
• AIDS—Modes of
Infection (read only)
– having unprotected sex
with a person who is
infected
– sharing a needle
(shooting drugs) with a
person who is infected
– being born from or
drinking the breast milk of
a woman who is infected.
Some people were infected
with HIV from getting a blood
transfusion from an infected
person.
Today, the blood supply is
carefully tested, and risk of
infection from a blood
transfusion is very low.
Organ Transplants
• If a person wanted to get an organ
transplant from another person why might
this be a problem?
• Why might they need to take immunosuppresent drugs?
• Why might these drugs be dangerous to
take?
Some Extra Online Videos for
Review
• Crash Course: Circulatory Overview
• http://www.youtube.com/watch?v=9fxm85
Fy4sQ&safe=active
• Bill Nye: Blood and Circulation Review:
• http://www.youtube.com/watch?v=WqiPBg
VbFDU&safe=active