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