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Immune sys - Coggle Diagram
Immune sys
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The body is constantly defending against attacks from pathogens. The first lines of defence against infection stop the pathogens from entering your body. These first lines are general defences, and are not specific to fight against certain types of pathogen. We call these non-specific barriers, and they can be either physical or chemical.
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The skin covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab. This prevents infection as the skin acts as a physical barrier. Parts of the body that do not have skin have developed other ways to prevent infection. For example, the eyes produce tears which contain enzymes, and these are known as chemical barriers.
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The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce mucus which traps pathogens before they can enter the lungs. When the nose is blown, the mucus, and any pathogens that are trapped within it, is removed.
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The trachea runs from the larynx (voice box) to the bronchi. The cells that line the trachea have hairs called cilia, which are much smaller than those in the nose. These are called ciliated cells. The ciliated cells waft their hairs and move mucus and pathogens upwards towards the throat where they are swallowed into your stomach.
Other cells called goblet cells create the mucus in order to trap pathogens. The production of mucus in your airways is a physical barrier.
The tracheal lining contains mucus-secreting goblet cells and epithelial cells bearing hair-like cilia.
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Stomach acid does not break down food in the same way as enzymes. It is part of the body’s non-specific first line of defence. It contains hydrochloric acid, and while it does us no harm, it is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water. Stomach acid is a chemical barrier against infection.
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Osmosis is when water moves from a less concentrated solution to a more concentrated solution through a partially permable membrane. A partially permable membrane only lets certain substance throught but not others.
As water moves into the more concentrated solution it weakens and the other solution (where the water came from) becomes more concentrated. When both sides are equally concentrated, the movement of water molecules is the same in both directions and level of water neither rises or falls. An example of osmosis is:
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cell more turgid and stiff, more able to stand up right.
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Diffusion is when particles spread from a high concentration to a low concentration. This is true for gases and particles dissolved in solution. The particles continue to move whilct there is a concentration gradient.A simple example of diffusion is when a person srays perfume, the particles in the perfume are at a high concentration when squirted but spread out and diffuse in a room. Two more exaples of diffusion within the body are:
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If pathogens pass the non-specific first line of defence, they will cause an infection. However, the body has a second line of defence to stop or minimise this infection. This is called the immune system, and mainly consists of two types of white blood cell called phagocytes and lymphocytes.
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Coloured scanning electron micrograph (SEM) of a macrophage white blood cell engulfing a tuberculosis (Mycobacterium tuberculosis) bacterium (orange).
Phagocytes are attracted to pathogens in the blood and bind to them. The phagocyte’s membrane surrounds the pathogen and engulfs it. Enzymes found inside the cell then break down the pathogen in order to destroy it. As phagocytes do this to all pathogens that they encounter, they are called non-specific.
Lymphocytes are another type of white blood cell. They recognise proteins on the surface of pathogens called antigens. Lymphocytes detect that these are foreign, ie not naturally occurring within the body, and produce antibodies. This can take a few days, during which time you may feel ill. The antibodies cause pathogens to stick together and make it easier for phagocytes to engulf them.
Some pathogens produce toxins which make you feel ill. Lymphocytes can also produce antitoxins to neutralise these toxins. Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, therefore the lymphocytes that produce them are called specific.
If your body encounters a particular antigen, your lymphocytes might recognise it. If they do, they clone themselves in order to make enough antibodies to destroy the pathogen. Memory cells are also created which remain in your bloodstream and produce a quick response if the antigen is encountered again. You are then said to be immune.
The best immunity comes from having fought off a disease. However, in some cases such as a serious disease that could prove fatal on first infection, this is not an option. Instead vaccination is used.