Germ Theory
• Microogranisms (microscopic particles) cause certain diseases – proposed by Louis
Pasteur – led to rapid
advances in understanding disease
Pathogens
• Many different types
• Bacteria are single-celled organisms. – cause illness by
destroying cells
– release toxic chemicals
Pathogens
• Viruses: – genetic material
surrounded by a protein coat
– force host cells to make more viruses
– very small
Fungi
• Can be multicellular or single-celled – take nutrients
from host cells
– occur in warm and damp places
Protozoa
• Single-celled organisms – use host cells to complete their life cycles
– take nutrients from host cell
How Pathogens Enter the Body
• Can be transferred by direct or indirect contact
• Indirect: – does not require
touching an infected individual
– touching an infected surface
– breathing in infected air
How Pathogens Enter the Body
• Vectors: – carry a pathogen
and transmit it into healthy cells
• Direct: – requires touching an
infected individual: • kissing
• sexual intercourse
• hand shaking
tick
The Immune System
• The body system that fights off infection and pathogens
• Many other tissues and systems help the immune system – Skin: a physical barrier to
infection. – Mucous membranes: trap
pathogens entering the body – Circulatory system:
transports immune cells
Immune Cells
• White blood cells (WBC’s) – attack infections inside the body
– phagocytes engulf and destroy pathogens
– T cells destroy infected cells
– B cells produce antibodies
Immune Proteins
• Fight off invading pathogens – Complement proteins weaken pathogen
membranes
– Antibodies make pathogens ineffective
– Interferons prevent viruses from infecting healthy cells
Immunity
• Prevents a person from getting sick – pathogens are destroyed
before sickness
• Passive immunity (occurs without an immune response):
– mother’s milk
– genetics
• Active immunity (occurs with an immune response)
Nonspecific Responses
• Are the same for every pathogen
• Ex: inflammation – blood vessels become leaky
– white blood cells move toward infection and damaged tissue
– characterized by swelling, redness, and pain
Nonspecific Responses
• Fever – blood temperature
increases
– low fevers stimulate white blood cells to mature
– high fevers can cause seizure, brain damage, and even death
Specific Responses
• Caused by immune cells
• Begin with antigen detection – antigens are surface
proteins on pathogens
– each pathogen has a different antigen
Memory Cells
• Produced by both Cellular and Humoral Immunity – specialized T and B cells
– provide acquired (active) immunity
Foreign Tissues
• Tissue rejection occurs in organ or tissue transplants
• Tissue rejection is the result of an immune respons – immune system detects protein markers on
the donor tissue
– makes antibodies against the donor’s tissue
Technology
• Many methods to control pathogens
• Antibiotics and antiseptics cause pathogens to burst
Technology
• Antiseptics: – kill pathogens outside the
body – do not target specific
pathogens • ex: vinegar, soap
• Antibiotics: • kill pathogens inside the body – target one specific bacterium
or fungus – not effective against viruses
Antibiotic Resistance
• 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
Vaccines
• Artificially produce acquired immunity
• Control pathogens and disease – given to 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
Leukemia
• Cancer of the bone marrow – characterized by immature white blood
cells
– causes weakened immune system
Leukemia
• Leads to opportunistic infections – occurs because
white blood cells cannot fight infections
– if immune system were healthy, would fight these infections
HIV
• Human immunodeficiency virus (HIV) is a retrovirus – targets the immune
system – attacks and weakens
the immune system – is transmitted by
mixing infected blood with a bodily fluid
HIV
• Leads to AIDS – HIV reproduces in
and destroys T cells
– the body cannot replace T cells fast enough
– T cells cannot help in immune responses