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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
Review: Parasite
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.
2
The B cell quickly activates and makes antibodies that fight the pathogens before you get sick.
3
Antigens in a vaccinetrigger an immune response, and memory B cells are made.
1memory B cells
How a vaccination provides immunity