Biology - Arif Sir's Handouts€¦ · Slide 43 of 50 ARIF ULLAH - ITHS - 01817721521 Acquired...

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ARIF ULLAH - ITHS - 01817721521

Biology

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40–2 The Immune System

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40-2 The Immune System

What is the function of the immunesystem?

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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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The immune system fights infection byproducing cells that inactivate foreignsubstances or cells.

This process is called immunity.

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The immune system includes two general categoriesof defense mechanisms against infection:

• nonspecific defenses

• specific defenses

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Nonspecific Defenses


Nonspecific defenses do not discriminate betweenone threat and another.

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What are the body's nonspecific defensesagainst invading pathogens?

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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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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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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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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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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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The Inflammatory Response

SkinWound

Phagocytes move intothe area and engulf thebacteria and cell debris

Capillary

Bacteriaenter thewound

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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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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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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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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


B cell

Plasmacell

Some B cells developinto plasma cells.Plasma cells produceantibodies that arereleased into thebloodstream.

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Specific Defenses


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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Biology - Arif Sir's Handouts€¦ · Slide 43 of 50 ARIF ULLAH - ITHS - 01817721521 Acquired...

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Transcript of Biology - Arif Sir's Handouts€¦ · Slide 43 of 50 ARIF ULLAH - ITHS - 01817721521 Acquired...