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Human defence systems and treatments GapFill
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Humans have many defences against pathogens, either to prevent their entry into the body or to destroy or inactivate them once they have gained entry. The role of defence systems is to prevent entry of any pathogen into the body. For example, the skin does this by acting as . The contains hairs that reduce a pathogen's entry way into the body and is lined with , which traps pathogens and allows them to be swallowed down to the stomach. Additionally, tears and saliva contain antibacterial enzymes called which act as a chemical defence.
The immune system produces a whole array of structures to defend against pathogens, including , which are produced by lymphocytes and act to clump pathogens together so they can then be engulfed by white blood cells. If the body has already encountered an antigen before, it will trigger the production of lymphocytes as part of the response to an antigen, and this will be much than the original response to the antigen.
As well as the body's natural defences, immunisation can also be used as a protective device, whereby containing a dead or an inactive form of a pathogen can be administered before infection to provoke a low-level immune response. There is also a range of , such as penicillin, which can be given to treat diseases caused by bacteria. Unfortunately these will not work on , which live inside cells, as treatments are needed which will harm the pathogen but not the host cells.
Drug trials can be long and expensive, and involve both preclinical trials on and clinical trials on humans. Medicine, and biological research in general, requires the growth of microorganisms, more properly called microorganisms.