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Protection Against Disease
The Immune System
Learning Objectives
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Explain how neutrophils and
macrophages prevent the spread of
pathogens
Phagocytes
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WBC work in
different ways and
there are 2 types of
phagocytic WBC
Neutrophils
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Multi lobed nucleus
Short lived (die after
phagocytosis)
Produced at rate of
80 million/minute
Starter
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codeword
The Immune System
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Is not a series of closely connected organs
It is made up of a series of unconnected sections including WBC
found in blood and lymph vessels and in tissue fluid
The main organs are the thymus, spleen and lymph nodes
LYMPH is formed when excess fluid drains from the tissues into
tubes called lymphatic vessels
Eventually this fluid is returned to the bloodstream but along
the way it passes though lymph nodes (small swellings along
lymph vessels)
Lymph nodes act as filters and are filled with lymphocytes that
collect and destroy bacteria and viruses. When the body is
fighting an infection, lymphocytes multiply rapidly and produce
a characteristic swelling of the lymph nodes.
White blood cells
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Immunity is the bodies ability to identify and
react to foreign materials
The bodies immune system is based on the
activity of various types of WBC (leucocytes)
The main types are
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Macrophages
Neutrophils
Lymphocytes
Macrophages
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Are phagocytic (encircle and engulf bacteria and
other particles) and involved in the immune response
Found mainly in connective tissue, basement
membranes of blood vessels and patrolling alveoli
Large numbers (patches of fixes phagocytes) line
passages in LYMPH NODES and in the spleen- here
they can destroy bacteria in the lymph as it flows
through to prevent infection from reaching the
general circulation
They recognise and ingest foreign cells and viruses
Phagocytosis
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What happens is the bacteria are engulfed forming a
PHAGOSOME. Small lysosomes fuse with the
phagocyte forming a phagolysosome, Lysozyme and
other hydrolytic enzymes and acid are poured in from
lysozome and the bacteria are digested. The soluble
products of digestion are absorbed into the
surrounding cytoplasm
This also results in some of the antigen molecules
becoming embedded in the macrophage cell
membrane
This alerts T and B lymphocytes to the infection
They are made in the bone marrow and are larger
that neutrophils
Stimulus for movement is thought to be some of the
chemicals liberated by ruptured blood cells, tissues
and bacteria - CHEMOTAXIS
Phagocytosis
Cytokines and Complement
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For phagocytosis to occur the
microorganisms must adhere to the csm
of the WBC. This is helped by
COMPLEMENT which are found in the
blood plasma and CYTOKINES which
are made by other WBC in response to
antigen. They also make phagocytes
more efficient at killing microorganisms
in the cell
Tasks
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Draw up a table of similarities and
differences between the neutrophil and
macrophage
Create a flow chart to describe the
stages of phagocytosis
Plenary
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Think of 2 questions to ask the others
about phagocytosis and prevention of
disease