stuff on the immune response

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The Immune System
Primary defences
This is a physical barrier that blocks pathogens from entering the body and also acts as a
chemical barrier by producing chemicals that are antimicrobial and can lower pH which
inhibits the growth of pathogens.
Mucous Membranes
They protect body openings that are exposed to the environment e.g. mouth, some
membranes secrete mucus which is a sticky substance that traps pathogens and
contains antimicrobial enzymes.
What is a immune response
A immune response is a body's reaction to a foreign antigen.
When a pathogen invades the body, the antigens on its cell surface are identified as
foreign which activates the immune response.
There are Four Main Stages Involved in the Immune Response
The first stage is where the Phagovytes Engulf Pathogens
This is where a phagocyte e.g. a macropage meets a pathogen where phagocytosis is
carried out.
Firstly a phagocyte recognises the antigen on a pathogen.
The cytoplasm of the phagocyte moves round the pathogen engulfing it.
The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the
A lysosome (an organelle taht contains digestive enzymes) fuses with the phagocytic
vacuole. The enzymes then break down the pathogen.
The phagocyte then presents the pathogen's antigens, it then sticks the antigens on its
surface to activate other immune system cells.
The Second Stage is Where the Phagocytes Activate T Lymphocytes
Another type of white blood cell called a T Lymphocyte, their cell membrane is covered
with receptors (each T Lymphocyte has a different receptor on its surface); these
receptors bind to antigens presented by the phagocytes.
When the receptor on the surface of a T Lymphocyte meets a complementary antigen-
the antigen then binds to it so each T lymphocyte will bind to a different antigen.

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This activates the T lymphocyte causing it to divide and differentiate into different types
of T lymphocytes that carry out different functions.
Some of these activated T lymphocytes release substances to activate B lymphocytes.
Some of these activated T lymphocytes attach to antigens on a pathogen and kill the
Some become memory cells.…read more

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They also have a hinge reigion which allows flexibility when the antibody binds to the
They also have constant regions which are the same in all antibodies. There are Disulfide
bridges to hold the polypeptide chains together.
How Antibodies Help to Clear an Infection
A way they help clear infection by agglutinating pathogens as each antibody has two
binding sites, so an antibody can bind to two pathogens at the same time causing
pathogens to clump together.…read more

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The secondary response often gets rid of the pathogen before you begin to show any
Primary response Secondary response
Pathogen Enteres for the first time Enters for a second time
Speed of Slow Fast
Cells activated B and T lymphocytes Memory cells
Symptoms Yes No
.…read more


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