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
Pathogens: – disease producing agents that are foreign to
the host
– Ex: Bacteria, protozoa, fungi, viruses, microbes
What Causes Infectious Disease?
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=Rpj0emEGShQ&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 “non-self” 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
• 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=PL2165FA6A0E3DDF85&safe=active
Immune Response (Read Only)
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=qdrpujSHfsU&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=A9HUN5kKK4A&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=k3CWxekGt7Y&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 immuno-suppresent 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=9fxm85Fy4sQ&safe=active
• Bill Nye: Blood and Circulation Review:
• http://www.youtube.com/watch?v=WqiPBgVbFDU&safe=active