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Chapter 47
The Body’s Defense Systems
Table of Contents
Section 1 Nonspecific Defenses
Section 2 Specific Defenses: The Immune System
Section 3 HIV and AIDS
Chapter 47
Section 1 Nonspecific Defenses
Objectives
• Identify a disease-causing agent.
• Describe bodies defenses against pathogens.
• Describe the inflammatory response.
White blood cells
(shown here in
gold) are the
defensive cells in
the body. White
blood cells locate
and destroy
pathogens, such
as the bacteria
shown.
What will
happen to the
bacteria after they
are surrounded?
The bacteria will
be engulfed in a
vacuole and
digested
by lysosomes.
Review
Cell Structure and Function (Ch. 4):
Describe the differences between eukaryotic cells and
prokaryotic cells.
• Eukaryotic cells have nuclei, membranebound organelles, and
divide through meiosis or mitosis.
• Prokaryotic cells do not have a nucleus or membrane-bound
organelles, and divide by binary fission.
Name some of the functions performed by cells.
• Reproduction
• Growth
• Metabolism
Review
Pathogens (Ch. 23 and Ch. 24):
List several differences between viruses and bacteria.
• Bacteria are alive, reproduce through binary fission, do
not require a host for reproduction, and require
nutrients.
• Viruses are not alive and require a host for
reproduction.
Explain how viruses replicate.
• Viruses insert their genetic material into a host cell,
which replicates the virus.
Chapter 47
Section 1 Nonspecific Defenses
Identifying Pathogens
• A pathogen is any agent that causes disease and
can be spread to humans
– What are common vectors of disease?
• air, food, water, or direct contact with an infected animal
or person.
• A disease that is caused by a pathogen is called
an infectious disease.
– What are examples of pathogens?
• bacteria, virus, fungi, or protist
Pathogens
Chapter 47
Section 1 Nonspecific Defenses
Koch’s Postulates
“Rules” for identifying a pathogen that causes a specific disease.
Koch's Postulates
Chapter 47
Section 1 Nonspecific Defenses
First Line of Defense: Barriers
• Nonspecific defenses
– What types of physical barriers do we have that
protect us from pathogens?
• the skin and mucous membranes
– skin also produces sweat, oils, and waxes, which
are toxic to many bacteria.
– mucous membrane is a layer of epithelial tissue
that covers internal surfaces of the body and
secretes mucus, a sticky fluid that traps
pathogens.
Chapter 47
Section 1 Nonspecific Defenses
Mucous Membranes
Chapter 47
Section 1 Nonspecific Defenses
Second Line of Defense: Nonspecific Immunity
– Nonspecific immunity works in the same way
against any pathogen.
– Nonspecific immunity includes
• the inflammatory response
• the temperature response
• certain proteins.
Section 1 Nonspecific Defenses
Chapter 47
Second Line of Defense: Nonspecific Immunity,
continued
• Inflammatory Response
– An inflammatory response is a series of events that suppress
infection and speed recovery.
– When cells are damaged they release chemical messengers,
such as histamine.
• Histamine is a substance that increases blood flow to the
injured area and increases the permeability of surrounding
capillaries.
Chapter 47
Section 1 Nonspecific Defenses
Second Line of Defense: Nonspecific Immunity,
continued
• Inflammatory Response, continued
– Fluids and white blood cells called phagocytes leak
through capillary walls to fight any pathogens that may
have entered the body.
• Phagocytes are cells that ingest and destroy foreign
matter, such as microorganisms.
Chapter 47
Section 1 Nonspecific Defenses
Second Line of Defense: Nonspecific Immunity,
continued
• Inflammatory Response, continued
– The most common phagocyte in the body is called a
neutrophil.
• A neutrophil is a large leukocyte that contains a
lobed nucleus and many cytoplasmic granules.
Chapter 47
Section 1 Nonspecific Defenses
Second Line of Defense: Nonspecific Immunity,
continued
• Inflammatory Response, continued
– A macrophage is a white blood cell that engulfs pathogens and
other materials.
– Another type of white blood cell that attacks pathogen-infected
cells is called a natural killer cell.
Chapter 47
Section 1 Nonspecific Defenses
Inflammatory Response
Inflammatory Response
Section 1 Nonspecific Defenses
Chapter 47
Second Line of Defense: Nonspecific Immunity,
continued
• Temperature Response
– When the body begins to fight pathogens, body
temperature may increase. This rise in temperature is
called a fever.
– The body triggers a fever in order to slow bacterial
growth or to promote white blood cell activity.
– Though a moderate fever can be helpful, high fever can
be dangerous.
Fever as Nonspecific Response
Chapter 47
Section 1 Nonspecific Defenses
Second Line of Defense: Nonspecific Immunity,
continued
• Proteins
– Proteins also provide nonspecific defenses.
• The complement system is a system of proteins that circulate
in the bloodstream and become active when they encounter
certain pathogens.
• Interferon is a protein released by cells infected with viruses
that enables nearby cells to resist viral infection.
Chapter 47
Section 2 Specific Defense: The Immune
System
Objectives
• Identify and describe the parts of the
immune system.
• Explain how the immune system recognizes
pathogens.
• Compare the actions of T cells and B cells in
the immune response.
Chapter 47
Section 2 Specific Defense: The
Immune System
The Immune System
• The immune system
includes the cells and
tissues that recognize
and attack foreign
substances in the
body.
• The components of
the immune system
are found throughout
the body.
Chapter 47
Section 2 Specific Defense: The
Immune System
The Immune System, continued
• What are the parts of the immune system?
– Bone marrow, the thymus, lymph nodes, the
spleen, adenoids, and tonsils.
Chapter 47
Section 2 Specific Defense: The
Immune System
The Immune System, continued
• The specialized cells of the immune system are
called lymphocytes.
– B cells are white blood cells that are made in the
bone marrow and complete their development
there or in the spleen. B cells make antibodies.
– T cells are cells that are made in the bone marrow
but complete their development only after
traveling to the thymus. T cells also participate in
many immune reactions.
Chapter 47
Section 2 Specific Defense: The
Immune System
Recognizing Pathogens
• Lymphocytes can
provide specific
defenses because they
recognize pathogens
by the antigens on
their surface.
• An antigen is any
substance that the
immune system does
not recognize as part
of the body.
Chapter 47
Section 2 Specific Defense: The
Immune System
Recognizing Pathogens, continued
• Because the lymphocytes
do not recognize the
antigen, they start a
specific attack known as
an immune response.
• Lymphocytes recognize a
pathogen with molecules
on their surface called
receptor proteins.
Chapter 47
Section 2 Specific Defense: The Immune
System
Recognizing Pathogens, continued
• An antigen has a
complementary threedimensional shape that
allows the receptor
protein to bind to it.
This is how the
lymphocyte recognizes
the antigen.
• Only the specific
receptor protein that is
complementary to the
antigen will be able to
bind there.
Section 2 Specific Defense: The Immune
System
Chapter 47
How a Cytotoxic T Cell
Recognizes an Infected Cell
Recognition of Pathogens
Immune Response
• An immune response is a two-part assault on a
pathogen. Both parts occur at the same time
and require a specialized lymphocyte called a
helper T cell.
• The two parts of the immune response are the
cell-mediated immune response and the
humoral immune response.
• T cells activate certain proteins that affect the
behavior of other immune cells. These proteins
are called cytokines.
Immune Response, continued
• Cell-Mediated Immune Response
– In the cell-mediated immune response,
cytokines activate more helper T cells and
another type of T cell called a cytotoxic T cell.
• Cytotoxic T cells recognize and destroy cells that have
been infected by a pathogen.
Chapter 47
Section 2 Specific Defense: The
Immune System
Immune Response, continued
• Cell-Mediated Immune Response, continued
– Also produced during the cell-mediated immune
response is a type of T cell called the suppressor T
cell.
– Suppressor T cells are thought to shut down the
immune response after the pathogen has been
cleared from the body.
Cell Mediated Immune Response
Immune Response, continued
• Humoral Immune Response
– The humoral immune response involves the action of B
cells and occurs when antibodies are activated within body
fluids.
– The humoral immune response occurs at the same time as
the cell-mediated immune response.
– During the humoral response, cytokines stimulate B cells
that have receptors that are complementary to the antigen
to divide and change.
Immune Response, continued
• Humoral Immune Response, continued
– Most B cells form plasma cells. A plasma cell is a
white blood cell that produces antibodies.
– Antibodies are defensive proteins that react to a
specific antigen or inactivate or indirectly
destroy toxins.
– Antibodies use various methods to disable a
pathogen or cause its destruction by nonspecific
responses.
Immune Response, continued
• Primary and Secondary Immune Responses
– The first time the body encounters an antigen, the
immune response is called a primary immune response.
– During this first encounter, the immune system fights
off the disease. After the disease is overcome, the
immune system creates memory cells.
• Memory cells are a B cell or T cell that will
recognize and attack the antigen or invading cell
during subsequent infections.
Immune Response, continued
• Primary and Secondary Immune Responses,
continued
– The second time the body encounters an
antigen, a secondary immune response occurs.
– During a secondary immune response, the
immune response is faster and more powerful.
– Most of the time, the secondary immune
response protects the body from reinfection
by a pathogen.
Chapter 47
Section 2 Specific Defense: The Immune
System
The Immune Response
Chapter 47
Section 2 Specific Defense: The Immune
System
The Immune Response, continued
Graphic Organizer
Chapter 47
Section 2 Specific Defense: The Immune
System
Primary and Secondary Immune
Responses
Primary Secondary Immune Response
Chapter 47
Section 2 Specific Defense: The
Immune System
Immunity and Vaccination
• Immunity is the ability to resist an
infectious disease.
• Immunity can come about in two ways:
surviving an initial infection or through
vaccination.
– Vaccination is the introduction of antigens into
the body to cause immunity.
Immunity and Vaccination,
continued
• Vaccines
– Vaccination usually involves an injection of a vaccine.
– A vaccine is a solution that contains a dead or weakened
pathogen or material from a pathogen that still contains
antigens.
– The immune system will produce a primary immune
response to the antigens. Memory cells can then provide a
quick secondary immune response if the antigen ever
enters the body again.
Vaccines
Problems of the Immune System
• Sometimes the immune system can react
to harmless antigens. Three examples of
this are allergies, asthma, and autoimmune
diseases.
• Allergies
– An allergy is a physical response to an antigen,
which can be a common substance that
produces little or no response in the general
population.
Chapter 47
Section 2 Specific Defense: The
Immune System
Allergy
Problems of the Immune System
• Asthma
– Allergies can trigger asthma. Asthma is a
respiratory disorder that causes the
bronchioles to narrow due to an overreaction
to substances in the air.
– During an asthma attack, the lining of the
bronchioles and other respiratory tissues may
also swell and become inflamed.
Problems of the Immune System
• AIDS (acquired immunodeficiency
syndrome) is a disease caused by HIV
(human immunodeficiency virus).
– Infection by HIV causes the immune system to
lose its ability to fight off pathogens and
cancers.
– HIV infection usually progresses to AIDS in
three phases.
Objectives
• Describe the relationship between HIV and AIDS.
• Distinguish between the three phases of HIV
infection.
• Identify the two main ways that HIV is
transmitted.
• Determine how the evolution of HIV affects the
development of vaccines and treatment.
The Course of HIV Infection
• AIDS (acquired immunodeficiency syndrome)
is a disease caused by HIV (human
immunodeficiency virus).
– Infection by HIV causes the immune system to
lose its ability to fight off pathogens and cancers.
– HIV infection usually progresses to AIDS in three
phases.
Chapter 47
Section 3 HIV and AIDS
AIDS
(Acquired Immunodeficiency Syndrome)
The Course of HIV Infection,
continued
• Phase I
– Phase I of HIV infection is called the asymptomatic
stage, because there are few or no symptoms of
the disease.
– During this period of the disease the viruses
increase rapidly due to replication.
– Phase I can last up to 10 years or more.
The Course of HIV Infection,
continued
• Phase II
– The beginning or worsening of symptoms
marks the start of the second phase of HIV
infection.
– B cells continue making antibodies, but T cells
begin to decline steadily as the virus continues
to replicate.
The Course of HIV Infection,
continued
• Phase III
– Phase III of HIV infection is the point where the
number of helper T cells drops so low that they
can no longer stimulate B cells and cytotoxic T
cells to fight invaders.
– AIDS is diagnosed when the helper T-cell count
drops below a certain level.
The Course of HIV Infection,
continued
• Phase III, continued
– AIDS is also diagnosed if an opportunistic infection has developed.
• Opportunistic infections are illnesses caused by pathogens
that produce disease in people with weakened immune
systems. These organisms usually do not create problems in
people with a healthy immune system.
– Drug therapy can slow the progress of HIV infection to AIDS, but
there is no cure for AIDS.
Chapter 47
Section 3 HIV and AIDS
Course of HIV Infection
Course of HIV
Transmission of HIV
• HIV is transmitted by the transfer of body
fluids containing HIV or HIV-infected cells.
• This most commonly occurs by sexual contact
with an infected person or by use of syringes
and hypodermic needles that have been
contaminated with blood containing HIV.
• HIV cannot be transmitted through casual
contact.
Chapter 47
Section 3 HIV and AIDS
Known Routes of HIV Transmission
Spread of AIDS
Vaccines and Treatments
• Effective treatments and vaccines for HIV are
difficult to create, because HIV has a rapid
evolution rate.
• Treatment is also difficult because HIV quickly
becomes resistant to antiviral drugs.
• Most HIV treatments are expensive and
require a complicated multidrug therapy.