Germ Theory Germ theory proposes that microorganisms cause diseases (not spirits, as once believed). – Proposed by Louis Pasteur – Led to rapid advances.

The Immune System

Germ Theory• Germ theory proposes that microorganisms cause diseases (not spirits, as

once believed).– Proposed by Louis Pasteur

– Led to rapid advances in understanding disease• Supported by Koch’s postulates.– Disease-causing agents, or particles, are called pathogens.

There are different types of pathogens • Bacteria are single-celled organisms:

– Cause illness by destroying cells, release toxic chemicals

– Ex: Food poisoning, MRSA

• Viruses are genetic material surrounded by a protein coat:

– Force host cells to make more viruses, small– Ex: Flu, Cold, HIV

• Fungi can be multicellular or single-celled:– Take nutrients from host cells by piercing healthy cells– Occur in warm and damp places – Ex: Athlete’s foot

• Protozoa are single-celled organisms.– Use host cells to complete their life cycles– Take nutrients from host cell– Ex: Malaria

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Different pathogens cause common infectious diseases

Pathogens can enter the body in different ways

• Pathogens can be transferred by indirect or direct contact.• Indirect contact does not require touching an infected

individual. – Touching an infected

surface– Breathing in infected

air

• Vectors :Carry a pathogen and transmit into healthy cells– Ex: Insects (ticks, mosquitoes, fleas), food

• Direct contact requires touching an infected individual. – Includes:

• Kissing• Sexual intercourse • Hand shaking

tick

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 is the (first) physical barrier to infection.– Mucous membranes trap pathogens entering the body.– 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, which

deactivate the pathogen.

antibody

pathogens

3 types of proteins fight off invading pathogens

– Complement proteins weaken pathogen membranes.

– Antibodies make pathogens ineffective. – Interferons prevent viruses from infecting

healthy cells.

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Immunity prevents a person from getting sick from a pathogen

• In all types of 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.• Having chicken pox

– Acquired Immunity occurs after given a vaccine.• Flu shot

Artificial methods are used to control pathogens

Antibiotics and antiseptics cause pathogens to burst

• Antiseptics kill pathogens outside of the body– Do not target specific

pathogens– Ex: Vinegar, Soap, Rubbing

Alcohol, Purel

• Antibiotics kill pathogens inside the body.– Target one specific bacterium

or fungus– NOT effective against viruses

Antibiotic Resistance• Overuse and misuse of antibiotics can cause medicines to

become ineffective.– Some bacteria in a population have genes that make them

immune to antibiotics.– These bacteria spread the gene, making the antibiotics

useless.A bacterium carriesgenes for antibioticresistance on a plasmid.

A copy of the plasmid is transferredthrough conjugation.

Resistance is quicklyspread throughmany bacteria.

• Vaccines control pathogens and disease– Injected with antibodies that have been exposed to the

pathogen. • Gives instant but short- term protection.

– Given mild or dead version of the pathogen. • Your body makes the antigens itself for long-term protection.• Memory B cells stay for a long time, ready for another attack from the

same organism.

Vaccines artificially produce acquired immunity

– Stimulates a specific immune response

– Allows immune system to respond quickly to infection

– Causes memory cells to be produced

– Has a fast response, a person will not get sick

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

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

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

1memory B cells

How a vaccination provides immunity