KEY CONCEPT 31.1Germs cause many diseases in humans.

Germ theory states that microscopic particles cause certain diseases.

– proposed by Louis Pasteur– led to rapid advances in understanding disease

• Disease-causing agents are called pathogens.

• Koch’s postulates support the theory- Pathogen must be present in every case disease is found- Pathogen must be isolated and cultured- Healthy animal must be injected- Pathogen must be collected, isolated, and identical to original

There are different types of pathogens.

1. Bacteria are single-celled organisms. – cause illness by destroying

cells – release toxic chemicals

2. Viruses are genetic material surrounded by a protein coat.– force host cells to

make more viruses – very small

3. Fungi can be multicellular or single-celled.– take nutrients from host cells– occur in warm and damp places

4. Protozoa are single-celled organisms.– use host cells to complete their life cycles– take nutrients from host cell

5. Parasites are multicellular organisms.– grow and feed on a host – possibly kill the host

• Different pathogen cause common infectious diseases.

Pathogens can enter the body in different ways.• Pathogens can be transferred by direct or indirect contact.• Indirect contact does not require touching an infected

individual. – touching an infected

surface– breathing in infected

air

• Vectors carry a pathogen and transmit it into healthy cells.

• Direct contact requires touching an infected individual. Includes: – kissing– sexual intercourse – hand shaking

tick

Summary 31.1

1. What conditions must be met before a specific pathogen is proved to cause a disease?

2. Name the five general types of pathogens. Provide an example of each.

3. Name three ways a pathogen can be spread.

4. Contrast a virus with a bacteria. How do they differ in ways that they affect cells in the body?

5. What is a vector? Provide 2 examples.

Ch 31.2 KEY CONCEPTThe immune systems consists of organs, cells, and molecules that fight infections.

Many body systems protect you from pathogens.• The immune system is the body system that fights off

infection and pathogens.• Many other tissues and systems help the immune system.

– Skin– Mucous membranes trap pathogens– The circulatory system transports immune cells.

Cells and proteins fight the body’s infections.• White blood cells attack infections inside the body.

– Phagocytes engulf and destroy pathogens. – T cells destroy infected cells.– B cells produce antibodies.

• Three types of proteins fight off invading pathogens.

– Complement proteins weaken pathogen membranes.– Antibodies make pathogens ineffective. – Interferons prevent viruses from infecting healthy cells.

antibody

pathogens

Immunity prevents a person from getting sick from a pathogen.• In all immunity, pathogens are destroyed before you get

sick.• Passive immunity occurs without

an immune response.– mother’s milk– genetics

• Active immunity occurs after aspecific immune response

• Which would vaccines be?

Summary 31.2

1. How does the immune system work with other body systems to prevent and fight disease?

2. How do phagocytes help to fight infection?3. Name the two types of immunities. Which

requires white blood cells? Explain.4. How do complement proteins differ from

antibodies?5. If a person had a disease that prevented

lymphocytes from maturing, how would the immune system’s response to infection change?

31.3 Key Concept: Many body systems work to produce nonspecific responses. • Nonspecific responses are the same for every pathogen.• In inflammation, blood vessels become leaky.

– white blood cells movetoward infection anddamaged tissue

– characterized by swelling, redness, and pain

capillary wallextracellular space

white blood cell

• In fever, body temperature increases.

– High fevers can cause seizure, brain damage, and even death.

– Low fevers stimulate white blood cells to mature.

Cells of the immune system produce specific responses.• Specific immune responses begin with the detection of

antigens.– Antigens are surface proteins on pathogens.– Each pathogen has a different antigen.

virus

antigens

pathogen

antigens

T cell

receptors activated T cells

antigens

memory T cells

• There are two specific immune responses.– Cellular immunity uses T cells to destroy infected body

cells.

• There are two specific immune responses.– Humoral immunity uses B cells to produce antibodies.

memory B cells

activated B cells

antibodies

B cell

T cell

pathogen

• Both responses produce memory cells.

– specialized T and B cells– provide acquired (active) immunity

B cellT cell

The immune system rejects foreign tissues.

• Tissue rejection occurs in organ or tissue transplants.– immune system detects protein markers on the donor

tissue– makes antibodies against the donor’s tissue

Summary 31.3 1. How does inflammation help the immune system to fight

pathogens?2. What is the main difference between cellular and

humoral immunity?3. What is tissue rejection, and why does it occur? 4. Why might it be beneficial for a person to get blood or

tissue donated from a relative instead of a non-related donor?

5. What are the differences between a specific and nonspecific immune response?

31.4 Many methods are used to control pathogens.• Antibiotics and antiseptics cause pathogens to burst.

• Antibiotics inside body• Antiseptic outside

Vaccines artificially produce acquired immunity.• Vaccines also control pathogens and disease.

– prevent illness– contain the antigen of a weakened pathogen

Vaccination provides immunity.

• stimulates a specific immune response

• causes memory cells to be produced

• allows immune system to respond quickly to infection

• has such a fast response, a person will not get sick

Antigens in a vaccinetrigger an immune response, and memory B cells are made.

1memory B cells

A memory B cell isstimulated when the real pathogen binds to it.

2

The B cell quickly activates and makes antibodies that fight the pathogens before you get sick.

3

31.5 Allergies occur when the immune system responds to harmless antigens.

• Allergies are caused by allergens.– Allergens: antigens that cause an allergic reaction.– Allergens cause inflammation responses.– Examples: foods, airborne, chemicals

• Allergens can cause anaphylaxis. – Anaphylaxis is an extreme inflammation response.– Blood vessels and airways become too porous.– Can cause death

In autoimmune diseases, white blood cells attack the body’s healthy cells.• Autoimmune diseases are failures of the immune system.

– White blood cells cannot recognize healthy cells.– Tissues fail because of attack.

Ch 31.6• Leukemia is cancer of the bone marrow.

– characterized by immature white blood cells – causes weakened immune system– Leads to opportunistic infections

HIV targets the immune system.

• The human immunodeficiency virus (HIV) is a retrovirus.– RNA– HIV causes host cell DNA to copy its RNA, then

incorporate it into the DNA of the cell– Lysogenic until triggered to lytic

• HIV infection leads to AIDS (Acquired Immune Deficiency Syndrome).– HIV reproduces in and destroys T cells.– The body cannot replace T cells fast enough.– T cells cannot help in immune responses.

HIV

T cell deadT cell

antibody

activatedB cell

Summary Review Questions1. What is the difference between specific and nonspecific

response?2. Summarize the steps the immune system takes when it your

body is vaccinated.3. Under what conditions is an antigen called an allergen?4. What is an autoimmune disease and why might it be

considered a failure of the immune system?5. How do AIDS and HIV differ?6. Which cells are affected by HIV and Leukemia? And what parts

of the immune system do the influence?