Chapter 40-2

Immune System

Immune SystemA series of defenses that guard your body against

diseaseFunction: to fight infection by producing cells that

inactivate foreign substances or cellsThis is called IMMUNITY

Pathogen: disease causing agents such as bacteria, virus, and fungi

Recognizes, attacks, destroys, & “remembers” each type of pathogen that enters the body

Produces specialized cells that inactivate the pathogen

Organs of theImmune System

Nonspecific DefensesDo not discriminate between 1 threat and

another (reacts the same no matter what)Include physical & chemical barriers1st Line of Defense:

1. Most important – SKIN2. mucus, saliva, tears, oil & sweat

glands2nd Line of Defense: inflammatory

response

SkinVery few pathogens can get across the layers

of dead cells on the surfaceWhen broken (cuts or wounds), pathogens

enter very easily & multiplyCauses symptoms of INFECTION:

1. swelling2. redness3. pain4. heat

Secretions of the BodyMucus, saliva and tears - all contain

LYSOZYME – enzymes that breaks down the cell walls of bacteria

Oil & sweat glands produce an acidic environment on the skin that kills many bacteria

Mucus in mouth & nose help trap pathogensStomach acids & digestive enzymes destroy

many pathogens that get in your stomach

Inflammatory Response A nonspecific defense reaction to tissue

damage caused by injury or infection1. Millions of white blood cells are produced

– which fight the infection2. Blood vessels near the wound expand,

allowing the WBCs to travel faster to infected tissue

3. WBCs engulf & destroy bacteria4. Area becomes swollen & painful5. Body release chemicals to increase body

temp. – fever – slows or stops the growth of the pathogen

6. Fever also causes heart rate to increase which pushes WBCs to infected tissue faster

White blood cell vs. Red blood cell

InterferonsProteins that help other cells resist viral

infectionsInterfere with the growth of the virusSlows down the progress of the infection &

gives the immune system time to respond

Specific DefensesIf a pathogen gets through the nonspecific

defenses, the body STARTS the IMMUNE RESPONSE

ANTIGENS: substances that trigger this response – viruses, bacteria

Cells in the immune system can recognize these antigens are called - lymphocytes

Lymphoctyes B Cells – provide immunity against antigens &

pathogens in body fluids - this is called HUMORAL IMMUNITYT-cells – provide defense against abnormal cells

& pathogens inside living cells. - this is called CELL-MEDIATED IMMUNITY

Humoral ImmunityWhen a pathogen enters the body, it is

recognized by a small amount of B cellsThese B cells grow & divide rapidly –

producing many memory B cells & Plasma cells

Plasma cellsPlasma cells release ANTIBODIES –

recognize & bind to antigens

Antibodies attack the pathogen until it has taken it over

Once infection is gone, the plasma cells die & stop producing antibodies

Memory B CellsRemember every pathogen that enters the

bodyAble to produce antibodies if exposed againGreatly reduces the chance of being

infected again

Antibody StructureShaped like a Y and has 2 binding sites to

connect with antigensThe different shapes give antibodies the

ability to recognize a large variety of antigens

Its estimated that a healthy adult can produce about 100 million different types of antibodies

Antigen-binding sites

Antigen Antibody

Cell-Mediated ImmunityThe body’s primary defense against its own

cells when they have become cancerous or infected by viruses

Also important in fighting infection by fungi & protists

Viruses & other pathogens can not be destroyed by antibodies alone

Process of cell mediated immunity1. T cells divide & change into Killer T cells,

Helper T cells, & Memory T cells2. Killer T cells find & destroy the pathogen

or foreign tissue that contains the antigen

3. Helper T cells produce Memory T cells4. Memory T cells remember the antigen in

case of future invasion5. Once pathogen is taken over, Suppressor

T cells shut down Killer T cells

HIV – Human Immunodeficiency Virus

Acquired Immunitywhen immunity is taken from outside the

body – not naturally madeTwo typesActive ImmunityPassive Immunity

Active ImmunityVaccination – injection of a weakened

form of a pathogen to produce immunityMore than 20 serious human diseases

can be prevented by vaccinationsModern vaccines stimulate the immune

system to create millions of plasma cells ready to produce specific types of antibodies

When the body reacts to the vaccines it is known as Active Immunity

Passive ImmunityWhen antibodies produced by other animals

against a pathogen are injected into the bloodstream

Last only a short timeCan develop naturally - passing from mother

to child through placenta or breast feeing or by deliberate exposure - vaccines for

malaria or when someone is bitten from snake or rodent