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