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ARIF ULLAH - ITHS - 01817721521
Biology
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ARIF ULLAH - ITHS - 01817721521
40–2 The Immune System
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40–2 The Immune System
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ARIF ULLAH - ITHS - 01817721521
40-2 The Immune System
What is the function of the immunesystem?
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40–2 The Immune System
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ARIF ULLAH - ITHS - 01817721521
40-2 The Immune System
The immune system is the body's main defenseagainst pathogens.
The immune system recognizes, attacks, destroys,and “remembers” each type of pathogen that entersthe body.
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40-2 The Immune System
The immune system fights infection byproducing cells that inactivate foreignsubstances or cells.
This process is called immunity.
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40–2 The Immune System
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40-2 The Immune System
The immune system includes two general categoriesof defense mechanisms against infection:
• nonspecific defenses
• specific defenses
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Nonspecific Defenses
Nonspecific Defenses
Nonspecific defenses do not discriminate betweenone threat and another.
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Nonspecific Defenses
What are the body's nonspecific defensesagainst invading pathogens?
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40–2 The Immune System
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Nonspecific Defenses
First Line of Defense
The first line of defense keeps pathogens outof the body.
This role is carried out by skin, mucus, sweat,and tears.
Your body's most important nonspecificdefense is the skin.
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Nonspecific Defenses
Few pathogens can penetrate the layers of dead cellsat the skin’s surface.
However, when the skin is broken, pathogens canenter the body and multiply.
As they grow, they cause the symptoms of aninfection, such as swelling, redness, and pain.
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Nonspecific Defenses
If pathogens enter the skin, mucus, saliva, and tears,contain lysozyme—an enzyme that breaks down thecell walls of many bacteria.
In addition, oil and sweat glands in the skin producean acidic environment that kills many bacteria.
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Nonspecific Defenses
Other nonspecific defenses include:
• Mucus in the nose and throat helps to trappathogens.
• Cilia in the nose and throat push pathogens awayfrom the lungs.
• Stomach acid and digestive enzymes destroypathogens.
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ARIF ULLAH - ITHS - 01817721521
Nonspecific Defenses
Second Line of Defense
If pathogens enter the body, the inflammatoryresponse is activated.
The inflammatory response is a nonspecificdefense reaction to tissue damage causedby injury or infection.
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Nonspecific Defenses
The Inflammatory Response
SkinWound
Phagocytes move intothe area and engulf thebacteria and cell debris
Capillary
Bacteriaenter thewound
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Nonspecific Defenses
When pathogens are detected, the immune systemmakes white blood cells, which fight the infection.
Blood vessels near the wound expand, and whiteblood cells move from the vessels to enter theinfected tissues.
Many are phagocytes, which engulf and destroybacteria.
The infected tissue may become swollen and painful.
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Nonspecific Defenses
The immune system releases chemicals thatincrease the core body temperature, causing a fever.
This high temperature slows or stops the growth ofpathogens. It also increases heart rate so white bloodcells get to the site of infection faster.
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Nonspecific Defenses
Interferon
Sometimes, virus-infected cells produce proteinsthat help other cells resist viral infection.
These proteins are named interferons becausethey “interfere” with the growth of the virus.
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Nonspecific Defenses
Interferons inhibit synthesis of viral proteins ininfected cells and help block viral replication.
This process slows the progress of infection andgives the specific defenses of the immune systemtime to respond.
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Specific Defenses
Specific Defenses
If a pathogen gets past the nonspecific defenses,the immune system reacts with a series of specificdefenses.
These defenses are called the immune response.
Any substance, such as a virus or bacterium, thattriggers this response is known as an antigen.
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Specific Defenses
The cells of the immune system that recognizespecific antigens are:
• B lymphocytes (B cells)
• T lymphocytes (T cells)
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Specific Defenses
B cells defend the body against antigens andpathogens in body fluids. This process is calledhumoral immunity.
T cells defend the body against abnormal cells andpathogens inside living cells. This process is calledcell-mediated immunity.
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Specific Defenses
Humoral Immunity
Humoral immunity produces antibodies.
An antibody is a protein that recognizes and bindsto an antigen.
An antibody is shaped like the letter “Y” and hastwo identical antigen-binding sites.
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Specific Defenses
Antibody Structure Antigen-bindingsites
Antigen Antibody
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Specific Defenses
Small differences in amino acids affect shapes ofbinding sites.
Different shapes allow antibodies to recognize avariety of antigens with complementary shapes.
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Specific Defenses
Plasma cells release antibodies.
Antibodies are carried in the bloodstream to attackthe pathogen.
As the antibodies overcome the infection, the plasmacells die out and stop producing antibodies.
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Specific Defenses
Once the body has been exposed to a pathogen,millions of memory B cells remain capable ofproducing antibodies specific to that pathogen.
These memory B cells greatly reduce the chance thatthe disease could develop a second time.
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Specific Defenses
If the same antigen enters the body a second time, asecondary response occurs.
The memory B cells divide rapidly, forming newplasma cells.
The plasma cells produce the specific antibodiesneeded to destroy the pathogen.
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Specific Defenses
HumoralImmunity
Memory Bcell
AntigenAntigen bindingto B cell
B cell
Plasma cell
Production of many morecells and antibodies
Second exposure to same antigen
Production ofmemory B cells
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Specific Defenses
AntigenAntigenbinding toB cell
B cell
Plasmacell
Memory Bcell
B cells grow anddivide rapidly
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Specific Defenses
AntigenAntigenbinding toB cell
B cell
Plasmacell
Some B cells developinto plasma cells.Plasma cells produceantibodies that arereleased into thebloodstream.
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Specific Defenses
AntigenAntigenbinding toB cell
B cell
Memory Bcell
Some B cellsdevelop intomemory B cells.
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Specific Defenses
Production of manymore cells and
antibodies
Second exposureto same antigen
Production ofmemory B cells
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Specific Defenses
Cell-Mediated Immunity
Cell-mediated immunity is the response againstabnormal cells and pathogens.
When viruses or other pathogens get inside livingcells, antibodies alone cannot destroy them.
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Specific Defenses
In cell-mediated immunity, T cells divide anddifferentiate into different types:
• Killer T cells destroy foreign tissue containing theantigen.
• Helper T cells produce memory T cells.
• Suppressor T cells shut down killer T cells whendone.
• Memory T cells cause secondary response.
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Specific Defenses
Cell-MediatedImmunity T cell
Macrophage
Helper T cell
Killer T cell
Infectedcell
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Specific Defenses
T cell
Macrophage
Antigens aredisplayed onthe surface ofmacrophage.
T cell binds toactivatedmacrophage.
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Specific Defenses
Helper T cell
T cell, activated bymacrophage,becomes a helperT cell.
Helper T cellactivates killerT cells and Bcells.
Killer T cell
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Specific Defenses
Infectedcell
Killer T cells bind toinfected cells, disruptingtheir cell membranes anddestroying them.
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Specific Defenses
Transplants
Killer T cells make acceptance of organ transplantsdifficult.
Cells have marker proteins on their surfaces thatallow the immune system to recognize them.
The immune system would recognize atransported organ as foreign and attack it. This isknown as rejection.
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Specific Defenses
To prevent organ rejection, doctors find a donorwhose cell markers are nearly identical to cellmarkers of the recipient.
Recipients must take drugs to suppress the cell-mediated immune response.
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Acquired Immunity
Active Immunity
Injection of a weakened or mild form of a pathogento produce immunity is known as a vaccination.
Vaccines stimulate the immune system to createmillions of plasma cells ready to produce specifictypes of antibodies.
Immunity produced by the body's reaction to avaccine is known as active immunity.
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Acquired Immunity
Active immunity may develop:
• after exposure to an antigen (fighting aninfection).
• from deliberate exposure to an antigen (vaccine).
Today, over 20 serious human diseases can beprevented by vaccination.
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Acquired Immunity
Passive Immunity
The body can also be temporarily protectedagainst disease.
If antibodies produced by other animals areinjected into the bloodstream, the antibodiesproduce a passive immunity.
Passive immunity is temporary because eventuallythe body destroys the foreign antibodies.
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Acquired Immunity
Passive immunity can develop naturally or bydeliberate exposure.
Natural immunity occurs when antibodies producedby the mother are passed to the fetus duringdevelopment or in early infancy through breast milk.
Passive immunity also occurs when antibodies areadministered to fight infection or prevent disease.
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40–2
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40–2
A fever is an example of the body's
a. nonspecific defenses.
b. specific defenses.
c. active immunity.
d. humoral immunity.
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40–2
The most important nonspecific defense yourbody has against disease is
a. inflammation.
b. cilia and mucus in the nose and throat.
c. the skin.
d. saliva.
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40–2
During pregnancy, a mother can pass antibodiesonto her developing baby, producing
a. active immunity.
b. passive immunity.
c. immunodeficiency.
d. cell-mediated immunity.
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40–2
Injection of a weakened or mild form of apathogen to produce immunity is known as a(an)
a. antibody.
b. vaccination.
c. antigen.
d. antibiotic.
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40–2
The kind of white blood cells involved in cell-mediated immunity are called
a. killer T cells.
b. B cells.
c. phagocytes.
d. platelets.
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