Transcript The Immune System

The Immune System
Chapter 37
Infectious Diseases
Section 1
Pathogens Cause Infectious Disease
• An infectious disease is caused when a
pathogen is passed from one organism to
another, disrupting homeostasis in the
organism’s body.
– Agents called pathogens are the cause of infections.
Some but not all types are bacteria, viruses,
protozoans, fungi and parasites.
Spread of Disease
• For a pathogen to spread, it must have both a
reservoir and a way to spread.
• A disease reservoir is a source of the pathogen
in the environment.
• Reservoirs might be animals, people or
inanimate objects such as soil.
Human Reservoirs
• Humans are the main reservoir for pathogens
that affect humans.
• They might pass indirectly or directly from other
humans.
• Pathogens that cause colds, influenza and
sexually transmitted diseases, such as HIV can
be passed without a person knowing he or she is
infected.
Animal Reservoirs
• Influenza and rabies are examples of human
disease that are caused by pathogens passed to
humans from other animals.
– Influenza can affect pigs and various types of birds.
– Rabies can infect domestic dogs and many wild
animals such as bats, foxes, skunks and raccoons.
Other Reservoirs
• Some bacteria found only in soil contains
tetanus bacteria.
– This can be found in deep wounds.
• Contaminated water or food is another reservoir
for pathogens.
– Sewage problems
– Food left out on the counter in contact with flies.
Transmission of Pathogens
• Direct Contact:
– Major transmission of pathogens. Diseases such as colds, infectious
mononucleosis, herpes and sexually transmitted diseases (STDs)
are caused by direct contact.
• Indirect Contact
– Some pathogens can be passed indirectly through air. When a
person coughs or sneezes they may pass along tiny mucous
droplets. By cleaning dishes, utensils and countertops with
detergent as well as washing hands can severely limit the exposure
to pathogens.
• Vectors
– Most common vectors are arthropods, which include biting insects
such as mosquitoes and ticks. Diseases like Lyme disease, malaria
and West Nile are spread by mosquitoes.
Symptoms of Disease
• After replication of the infected disease it can kill
living cells and release harmful toxin chemicals
into the bloodstream.
• Outward symptoms may include fever, chills,
shortness of breath, rash, sneezing and
coughing to name a few.
Treating & Fighting Diseases
• A medical professional may prescribe a drug to
help the body fight a disease.
• One type of prescription drug is an antibiotic.
– It is a substance that can kill or inhibit the growth of
other microorganisms.
– However in the last 60 years bacteria have become
resistant to antibiotics.
The Immune System
Section 2
Nonspecific Immunity
• At the time of birth the body has a number of
defenses in the immune system that fight off
pathogens.
• These defenses are nonspecific because they
are not aimed at a specific pathogen.
• Nonspecific immunity helps slow the progression
of the disease, it is the first line of defense.
(Examples of Non-Specific) Barriers
• Skin:
– The simplest way of preventing foreign organisms from entering the
body.
– This major line of defense is the unbroken skin and its secretions.
– By forming a barrier, the layers of dead skin cells help protect against
invasion by microorganisms.
• Chemical:
– Saliva, tears, and nasal secretions contain the enzyme lysozyme,
which breaks down bacterial cell walls which kills pathogens.
– Mucus blocks airways within the body which stimulates coughing and
sneezing. Eventually it is eliminated from the body.
– Hydrocholric acid from the stomach aids in digestion, but also kills
many microorganisms found in food that could cause disease.
Nonspecific responses to invasion
• Cellular defense:
– One cellular defense is phagocytosis.
• White blood cells, especially neutrophils and macrophages, surround and internalize
foreign microorganisms. The phagocytes release digestive enzymes and other
harmful chemicals which destroy the pathogen.
– Complement proteins also aid in the process.
• Interferon:
– Virus infected cells secrete a protein called interferon, which binds to
neighboring cells and stimulates these cells to produce antiviral proteins
which can prevent viral replication.
• Inflammatory response:
– When pathogens damage tissue, chemicals are released by both the
invader and the cells of the body.
– These chemicals attract phagocytes to the area, increase blood flow and
make blood vessels more permeable to allow WBC’s to escape to the
infected area. In this area there might be pain, heat and redness.
• Lymphatic system:
Specific Immunity
– It includes organs and cells that filter lymph and blood and destroy foreign
microorganisms.
– It also absorbs fat.
– Lymph is the fluid that leaks out of capillaries to bathe body cells.
• Lymphatic organs:
– Lymphocytes are a type of WBC that is produced in red bone marrow.
– Lymphatic organs include: lymph nodes, tonsils, spleen, thymus and
diffused lymphatic tissues found in mucous membranes in the intestine,
respiratory, urinary and genital tracts.
– The lymph nodes filter the lymph and remove foreign materials from
lymph.
– The spleen stores blood and destroys damaged RBC’s.
– The thymus gland produces T-cells.
B Cell Response
• Antibodies are proteins produced by B lymphocytes that
specifically react with a foreign antigen.
– An antigen is a substance foreign to the body that causes an
immune response; it can bind to an antibody or a T-cell.
• In the lymph nodes, the macrophage, with the
processed antigen on its surface, binds to a type of
lymphocyte called a helper T cell.
– The helper T cell activates antibody secretion in B cells and
another type of T cell.
What the helper T-cell does…
• The activated helper T cell reproduces, binds processed
antigens, and attaches to a B cell.
• The new helper T cell continues the process of binding
antigens, attaching to B cells, and reproducing.
• Once an activated helper T cell binds to a B cell holding
an antigen, the B cell begins to manufacture antibodies
that specifically bind to the antigen.
• The antibodies can enhance the immune response by
binding to microorganisms, making them more
susceptible to phagocytosis and by initiating the
inflammatory response.
T Cell Response
• Once helper T cells are activated by an antigen,
helper T cells can also bind to and activate a
group of lymphocytes called cytotoxic T cells.
• Cytotoxic T cells destroy pathogens and release
chemicals called cytokines.
– This chemical stimulates the cells of the immune
system to divide and recruit immune cells to an area
of infection.
Passive Immunity
• Temporary protection occurs when antibodies
are made by other people or animals and are
transferred or injected into the body.
• Passive immune therapy is available for people
who have been exposed to hepatitis A and B,
tetanus, and rabies.
Active Immunity
• Active immunity occurs after the immune system is
exposed to disease antigens and memory cells are
produced.
– Memory cells are long-living cells that are exposed to the
antigen during the primary immune response. These cells
help protect the body by reducing the likelihood of developing
the disease if exposed again to the same pathogen.
• Immunization (vaccination) is the deliberate exposure of
the body to an antigen so that a primary response and
immune memory cells will develop.
Immune System
• The immune system and the circulatory
system work together to defend the
body against antigens.
Properties of Viruses
･no membranes, cytoplasm, ribosomes, or
other cellular components
･they cannot move or grow
･they can only reproduce inside a host cell
(therefore not considered “living”)
･they consist of 2 major parts - a protein
coat(capsid), and hereditary material (DNA or
RNA)
･they are extremely tiny, much smaller than a
cell and only visible with advanced electron
microscopes
Parasytic Nature
･Obligate intracellular parasites
･Specific to their hosts (human, dog, some can
cross species)
･They can only attack specific cells.
-The common cold is a virus that specifically
attacks cells of the respiratory track (hence
the coughing and sneezing and sniffling). HIV
virus specifically attacks white blood cells
Active Immunity: Vaccines
• Artificially acquired active immunity
• Consists of: dead or weakened bacteria
or viruses, OR a toxoid (a toxin from an
infectious organism that is chemically
altered to avoid toxic effects)
• Vaccines are typically injected or
inhaled
Vaccines
• Include antigens that stimulate an immune
response without producing severe
symptoms of the disease
• Vaccines work by stimulating antibody
production without causing disease
• Common Vaccinations: typhoid fever,
cholera, whooping cough, tetanus, polio,
chickenpox, measles, mumps, rubella,
influenza, hepatitis (A & B), bacterial
pneumonia
Immune System Failure
• The two most likely diseases to decrease the
effectiveness of the immune system are HIV and
AIDS.
–
HIV- Human immunodeficiency virus
–
AIDS- Acquired immunodeficiency syndrome
• When infected with HIV the CD4+ cells (like helper T
cells) become HIV factories.
• Over time, the number of helper T cells in an infected
person decreases, making a person less able to fight
disease.