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Section 6.1 ­ Defence Mechanisms


A disease is an interaction between the pathogen and the body's various
defence mechanisms. Sometimes the pathogen overwhelms the defences, and
the individual dies. Sometimes, the defence mechanisms overwhelm the
pathogen and the individual makes a full recovery. The body's defences are
now better…

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Section 6.2 ­ Phagocytosis

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For a pathogen to infect the body it must at first gain entry. The body's first
line of defence is to form a physical or chemical barrier. Should this fail, bring on
the white blood cells (there are two types: phagocytes and lymphocytes).
Lymphocytes are involved in immunity, and…

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Chemical products of the pathogen act as attractants which draw the
phagocyte towards it.

Pathogens are engulfed by phagocytes in the form of vesicles which are
formed on the cell-surface membrane.

Phagocytes attach themselves to the surface of the pathogen.

They engulf the pathogen to form a vesicle known as…

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The initial response of the body to infection is non-specific. The next phase is
the specific response that confers immunity, the ability of organisms to resists
infection by protecting against disease-causing microorganisms that invade
their bodies. It involves the recognition of foreign material ­ antigens.


Any part of…

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T ­ Lymphocytes can distinguish foreign material from the body's own tissue
1) Phagocytes that have engulfed and broken down a pathogen present
some of its antigens on its own cell-surface membrane.
2) Body cells invaded by a virus also manage to present some of the viral
antigens on…

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Section 6.4 ­ B Cells and Humoral Immunity


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In section 6.3 we saw the first phase of the specific response to infection is the
cloning of the relevant T cells to build up their numbers. Some of these T cells
produce factors that stimulate B cells to divide, which are involved in the next
stage of the specific…

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3. T helper cells attach to the processed antigens and B cells thereby
activating them.

4. The B cells are now activated to divide by mitosis to give a clone of the
plasma cells.

5. The cloned plasma cells produce antibodies that exactly fit the antigens
on the pathogens surface.…

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Monoclonal antibodies

A pathogen entering the body is likely to have hundreds of different antigens
on its surface. Each antigen will induce a different B cells to divide and clone its
self. Each clone will produce a different antibody known as a polyclonal

Obviously, it is of considerable medical…


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