The Immune Response (2.2.2)

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What is the immune response?
The ways in which certain cells respond when pathogens enter the body.
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What is a non-specific response?
These responses always work in the same way regardless of what the pathogen is.
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What are our primary defence mechanisms?
Skin, mucus membranes, stomach acid, tear ducts.
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How does the skin defend?
Epidermis is made from cells called teratinocytes. These are dead when they read the surface and contain keratin which is a barrier for pathogens.
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How do the mucus membranes defend?
Ciliated epithelium and goblet cells trap and waft mucus containing pathogens to the back of the throat to be swallowed.
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How does stomach acid defend?
Hydrochloric acid destroys most pathogens- their enzymes and proteins would be denatured by the lower pH.
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How do tear ducts defend?
Secrete substances over the front of the eye, containing enzymes to break down bacteria.
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What is the second line of defence?
Further non-specific responses of phagocytosis and the inflammatory response.
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What is phagocytosis?
A process carried out by neutrophils and monocytes which are WBCs. They engulf and digest non-self particles in the blood stream or tissues.
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Where are the neutrophils and monocytes made?
In the bone marrow by differentiation of stem cells.
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What do the monocytes do?
Move into tissues where they become known as macrophages. They are long living and will survive even after they've taken in and destroyed pathogens.
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What do the neutrophils do?
They are short lived and often die after taking in and destroying pathogens. New ones are constantly being made.
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What are the 3 ways phagocytes identify bacteria in the body?
Cells damaged by bacteria release cytokines- attract phagocytes to area. Bacteria have different antigens to our cells so are recognised as non-self. Molecules from our own plasma attach to bacteria so phagocytes can recognise them.
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Describe the process of inflammation?
Damaged tissues release histamine- vasodilation of arterioles in damaged area. Promotes chemical reactions- blood clotting & healing. Capillaries in area more permeable, more tissue fluid forms-swelling. More phagocytes to area, destroy bacteria.
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When does the inflammation process stop?
Once any bacteria is destroyed and tissue is repaired.
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What is the third like of defence?
The specific immune response. The cells involved can attack pathogens without causing harm to any other cells in the body. They can distinguish between self and non-self.
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What is an antigen?
A macromolecule usually made from glycoprotein found on the surface of the cells.
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What is an antibody?
Glycoprotein made in response to non-self antigen. Made from 4 polypeptide chains held by disulphide bonds- 2 heavy and 2 light. Flexible hinge region allows to change shape when attaching to pathogen. Variable region is different shape for each type
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What are the two types of lymphocyte?
B-lymphocytes- produced and develop in bone marrow. T-lymphocytes- produced in bone marrow, develop in thymus gland in neck.
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What do the lymphocytes look like?
Both are small WBCs, that look identical to each other.
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How many types of B-lymphocyte are there?
Approximately 10 million different types. Each has a different shaped protein receptor on its plasma membrane.
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What does the B-lymphocyte produce?
An antibody corresponding to the shape of its surface receptor.
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What does a B-lymphocyte do?
Pathogen enters body, one kind of B-lymphocyte will have receptors which fit the antigens on pathogen. Correct B-lymphocyte will have to be found.This takes time, the person may develop symptoms of infection. When it's found it will divide.
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What is clonal expansion?
B-lymphocyte divides by mitosis to produce clones. Some become plasma cells- make antibodies to deal with pathogen, short lived. Some become memory cells- remain in body for long time, pathogen enters they recognise it & divide to give plasma cells.
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What are the 5 different ways that antibodies can destroy bacteria?
Agglutination. Precipitation. Neutralisation. Lysis. Opsonins.
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What is agglutination?
The antibodies hold bacteria close to each other so they clump together. This makes it easier for phagocytes to engulf them.
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What is precipitation?
Antibodies can cause soluble antigens on pathogens to precipitate, making them easier to be engulfed by phagocytes.
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What is neutralisation?
If pathogens produce toxins in our bodies, antibodies can bind to these, neutralising them so they can't harm the body.
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What is lysis?
Antibodies can attract enzymes to attach to pathogens. The enzymes then break the pathogen down.
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What are opsonins?
Antibodies can act as opsinins, which means they can attach to a pathogen using their specific binding site and attaching to a phagocytic WBC at the other end. This holds the phagocyte close to the bacterium making it easier to engulf it.
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Where do antibodies deal with pathogens?
In the bloodstream. Once pathogens are inside body cells, T-lymphocytes are needed to deal with them.
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What is antigen presentation?
Phagocyte engulfs virus, then presents the viral non-self antigens on the surface of its cell.
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What is clonal selection?
The correct T-lymphocyte is selected from millions in the body- it has surface receptors complementary to presented antigens.
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What happens to the selected T-lymphocyte?
It undergoes clonal expansion to deal with the particular infection.
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What happens to the cloned T-lymphocytes?
They differentiate into 3 different types. T-killer lymphocytes, T-helper lymphocytes and T-suppressor lymphocytes.
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What do T-killer lymphocytes do?
Kill any body cells infected with the virus. They release chemicals called interferons to show they are damaged.
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What do T-helper lymphocytes do?
Secrete chemicals called cytokines which carry out cell signalling. This stimulates further phagocytosis. It also stimulates B-cells to produce more antibodies. And it stimulates the continued division of T-killer cells.
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What do T-suppressor lymphocytes do?
These inhibit the immune response once the pathogen has been dealt with.
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What do T-killer and T-helper lymphocytes produce?
T-memory cells to respond quickly if the same pathogen enters the body again.
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Why does the immune system show good examples of cell differentiation?
B-lymphocytes differentiate into plasma cells and memory cells. T-lymphocytes differentiate into helper, killer, suppressor and memory cells.
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Why would a B-lymphocyte have lots of RER, golgi and mitochondria?
The antibodies are made from protein on the ribosomes at the RER. They are modified by the golgi into glycoproteins. All of this requires energy from cell respiration in the mitochondria
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Describe what happens when you first get an infection.
Pathogen 1st enters body. Few lymphocytes with receptors to fit antigens. Takes time for lymphocytes to find & bind to pathogen. Takes time to clone. In delay, pathogen divides in tissues. Harm caused makes person feel ill.
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Describe how immunity develops.
Body survives 1st attack by pathogen, memory cells stay in blood. Same pathogen enters again, memory cells trigger faster antibody production. This is secondary response. It happens more quickly so we become immune to a disease when we've had it once
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What information is communicated in cell signalling?
Identification. Distress signals. Antigen presentation. Instructions.
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What is identificaton?
The pathogen carries antigens on its cell surface which are non-self and detected by body cells.
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How are distress signals shown?
Parts of the pathogen end up attached to the body cell membrane. This acts as a distress signal to trigger other cells from the immune system and act as markers for T-killer cells which recognise the infected cell and destroy it.
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What is antigen presentation?
Macrophages engulf pathogens, then display the pathogen's antigens on its own cell surface. This antigen presentation will then select appropriate lymphocytes to deal with the pathogen.
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What instructions are communicated?
Cytokines are released by cells of the immune system. These act as instructions for their target cells. They act over short distances at low concentrations. For example, chemicals are released by macrophages to attract neutrophils to the pathogens.
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Card 2

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What is a non-specific response?

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These responses always work in the same way regardless of what the pathogen is.

Card 3

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What are our primary defence mechanisms?

Back

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Card 4

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How does the skin defend?

Back

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Card 5

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How do the mucus membranes defend?

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