These parts of the human body have non-specific defence systems against pathogens: skin, ____, trachea and bronchi and the stomach. Parts of the body that do not have skin have developed other ways to prevent ____. For example, the ____ produce tears, which contain ____. These destroy pathogens and are ____ barriers. Skin The skin covers almost all parts of the body to prevent infection from ____. If it is cut or grazed it immediately begins to heal itself, often by forming a ____, which prevents ____ as the skin acts as a ____ barrier preventing the entry of invading microorganisms. Scabs are formed when ____ in the blood release chemicals that cause soluble proteins to form a mesh of insoluble fibres across the wound stick together to form ____ that get stuck in the mesh. ____ also get stuck in the mesh, forming a clot. Nose The nose has internal ____ which act as a ____ barrier to infection. Cells in the nose produce ____. This traps pathogens before they can enter the lungs. When the nose is blown mucus is removed with any pathogens trapped within it. * * * Trachea and bronchi The trachea runs from the nose towards the ____. The ____ that line the trachea also have hairs called ____ (much smaller than those in the nose). They waft their hairs and move mucus and pathogens upwards towards the throat where it is swallowed into your ____. Other cells called goblet cells create the mucus to trap pathogens. The production of mucus in your airways is a physical barrier. Stomach Stomach ____ does not break down food. It is part of the body's ____ first line of defence. It is ____ and while it does us no harm, it is strong enough to kill any pathogens that have been caught in ____ in the airways or consumed in food or water. Stomach acid is a ____ barrier against infection. If a pathogen enters the body the immune system tries to destroy the pathogen. White blood cells help to defend against pathogens. * * * PHAGOCYTOSIS: Phagocytes surround any pathogens in the blood and ____ them. They are attracted to pathogens and bind to them. The phagocyte's membrane surrounds the pathogen and ____ found inside the cell break down the pathogen, in order to destroy it. As phagocytes do this to all pathogens that they encounter, we call them ____. ANTIBODY PRODUCTION: White blood cells called lymphocytes recognise proteins on the surface of pathogens called ____. If they detect foreign antigens on a cell they produce ____. This can take a few days, during which time you may feel ill. The antibodies cause pathogens to ____ and make it easier for ____ to engulf them. ANTITOXIN PRODUCTION: Some pathogens produce ____ which make a person feel ill. Lymphocytes can also produce ____ to neutralise these toxins. Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, thus the lymphocytes that produce them are called ____. PHAGOCYTOSIS: Phagocytes surround any pathogens in the blood and ____ them. They are attracted to pathogens and bind to them. The phagocyte's membrane surrounds the pathogen and ____ found inside the cell break down the pathogen, in order to destroy it. As phagocytes do this to all pathogens that they encounter, we call them ____. * * * ANTIBODY PRODUCTION: White blood cells called lymphocytes recognise proteins on the surface of pathogens called ____. If they detect foreign antigens on a cell they produce ____. This can take a few days, during which time you may feel ill. The antibodies cause pathogens to ____ and make it easier for ____ to engulf them. * * * ANTITOXIN PRODUCTION: Some pathogens produce ____ which make a person feel ill. Lymphocytes can also produce ____ to neutralise these toxins. Both the antibodies and antitoxins are highly specific to the antigen on the pathogen, thus the lymphocytes that produce them are called ____. If an individual encounters a particular antigen, ____ recognise the antigen, and clone themselves to make enough ____ to destroy the invading organism. Memory cells are also made, which remain in the ____ and produce a ____ response if the antigen is encountered again. In this situation, a person is said to be ____.

4.3.1.6 Human defence systems

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