Chapter 47 Table of Contents

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The Body’s Defense Systems

Chapter 47

Chapter 47 Objectives

• Summarize Koch’s postulates for identifying a disease-causing agent.

• Describe how the skin and mucous membranes protect the body against pathogens.

• Describe the steps of the inflammatory response.

• Analyze the roles of white blood cells in fighting pathogens.

• Explain the functions of fever and proteins in fighting pathogens.

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Chapter 47 Identifying Pathogens

• A pathogen is any agent that causes disease and can be spread to humans through the air, food, water, or direct contact with an infected animal or person.

• A disease that is caused by a pathogenic bacteria, virus, fungi, or protist is called an infectious disease.

• Koch’s postulates are “rules” for identifying the particular pathogen that causes a specific

disease.

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Chapter 47

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Visual Concept

Pathogen

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Chapter 47 Koch’s Postulates

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Chapter 47

Visual Concept

Koch’s Postulates

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Chapter 47 First Line of Defense: Barriers

• Nonspecific defenses, such as the skin and mucous membranes, are barriers to potential pathogens.

– In addition to being a physical barrier to

pathogens, skin also produces sweat, oils, and waxes, which are toxic to many bacteria.

– A mucous membrane is a layer of epithelial

tissue that covers internal surfaces of the body and secretes mucus, a sticky fluid that traps pathogens.

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Chapter 47 Second Line of Defense: Nonspecific Immunity

• If a pathogen gets past the skin and the mucous membranes, the body triggers the second line of defense, which is nonspecific immunity.

– Nonspecific immunity works in the same way against any pathogen.

– Nonspecific immunity includes the

inflammatory response, the temperature response, and certain proteins.

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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.

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Chapter 47 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.

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Chapter 47 Second Line of Defense: Nonspecific Immunity, 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.

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Chapter 47 Second Line of Defense: Nonspecific Immunity, 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.

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Chapter 47 Inflammatory Response

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Chapter 47

Visual Concept

Inflammatory Response

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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 fevesr can be dangerous.

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Chapter 47

Visual Concept

Fever as Nonspecific Defense

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Chapter 47 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.

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Section 2 Specific Defense: The Immune System

Chapter 47 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.

• Relate vaccination to immunity.

• Distinguish between allergy, asthma, and autoimmune disease.

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Chapter 47 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.

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Chapter 47 The Immune System, continued

• Bone marrow, the thymus, lymph nodes, the spleen, adenoids, and tonsils are all part of the immune system.

• Each part of the immune system plays a special role in defending the body against pathogens.

• The specialized cells of the immune system are called lymphocytes. Lymphocytes are white

blood cells that exists in two primary forms: T and B cells.

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Chapter 47 The Immune System, continued

• 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 Recognizing Pathogens, continued

• An antigen has a complementary

three-dimensional 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.

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Chapter 47 How a Cytotoxic T Cell Recognizes an

Infected Cell

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Chapter 47

Visual Concept

Recognition of Pathogens

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47

Visual Concept

Cell-Mediated Immune Response

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 The Immune Response

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Chapter 47 The Immune Response, continued

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Chapter 47 Primary and Secondary Immune Responses

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Chapter 47

Visual Concept

Primary and Secondary Immune Response

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47

Visual Concept

Vaccine

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Section 3 HIV and AIDS

Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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.

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Chapter 47 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 creat 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.

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Chapter 47 Course of HIV Infection

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Chapter 47 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.

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Chapter 47 Known Routes of HIV Transmission

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Chapter 47

Visual Concept

Course of an HIV Infection

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Chapter 47 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.

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Chapter 47

Visual Concept