The Second Line of Defence
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Transcript of The Second Line of Defence
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The Second Line of DefenceExpected Learning: to investigate the second line of defence of immunity, including phagocytes, natural killer cells, inflammation and complement proteins.
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Second Line of Defenceo As mentioned in Eden
and Theresa’s presentation, the body has a first line of defence against infection
o If this fails, a second line of defence must take place in the body
o The following are a number of way in which the body’s second line of defence takes action against disease and infection
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Phagocytes Phagocytes are white blood cells
that engulf and destroy micro-organisms and other foreign material
They are produced in the bone marrow
They include neutrophils (most common white blood cell) and monocytes (largest white blood cell)
Bacteria and other microorganisms engulfed by phagocytes are broken down by enzymes and other factors released into the vacuoles containing the foreign material, and the bacterium is killed.
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Natural killer cells
Type of white blood cell that kills virus-infected body cells
Most aggressive of all the white blood cells
Important in the fight against cancer
In the picture, the natural killer cell is the purple cell, attacking the foreign green cell
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Complement Proteins About 20 different complement
proteins circulate in the blood They work in different ways:
-Stimulating phagocytes to become more active
-Coating microorganisms so that they are more easily
identified by phagocytes-Lysing (break open)
bacterial membranes-Attracting phagocytes to
the site of infection Can help with specific immune
responses (that we will learn later on)
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InterferonoGroup of proteinso Secreted by some
cells when they are infected by virus particles
oAct on uninfected cells to make then more resistant to the virus
o If a person develops a cold or flu, interferon has failed to prevent infection
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CytokinesProtein molecules that act
as messengers between cells.
Produced by virtually all cells of the immune system
Communicate with cells in other body systems, including the nervous system
A cell can only respond to a message from a cytokine if it has an appropriate receptor.
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Inflammation Inflammation increases the blood
supply to a site of infection, thereby increasing the number of white blood cells at the site
Caused by a number of plasma enzyme systems such as serotonin
Serotonin increases dilation of arterioles and permeability of vascular tissue (allowing more blood cells to pass through)
Phagocytes are carried to the area The used up white blood cells that
have already engulfed bacteria are stored in the form of pus in the infected area
Skin eventually repairs as infection disappears, reducing inflammation over time
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Page 249 of textbook
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Past Exam Questions
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Answers
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Reflection and Homework
What have you learnt about the second line of defence against infection?
How do complement proteins assist phagocytes? What is pus?
Quick check 4 - 7 Biochallange 1