Human defence systems and treatments GapFill

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  pathogenicnon-specificantimicrobialspecificphysicalimmune defence systems, such as the skin, is to prevent entry of any pathogen into the body. The skin does this by acting as a physical barrier and also by secreting  phagocytesantitoxinsantigensvaccinesantimicrobial compoundsantibiotics. The  mouthnosevaginaearlungeye contains hairs that act as a physical barrier and is lined with  watersalivabilelysozymesmucuscilia, which traps pathogens and allows them to be swallowed down to the stomach. Additionally, tears and saliva contain antibacterial enzymes called  antibodiesamylaseslysozymesproteasespenicillinlipases.

The immune system produces a whole array of structures to defend against pathogens, including  lysozymeslymphobodiesphagocytesantitoxinsantigensantibodies, which are produced by lymphocytes and act to clump pathogens together. They can then be engulfed by white blood cells called  erythrocytesphagocytesantigensantibioticsantitoxinsleukocytes.

As well as the body's natural defences,  a vaccinean antibodyan antibiotican antigena cella painkiller containing a dead or an inactive form of a pathogen can be administered before infection to provoke a low-level immune response, and there is a range of  pesticidesvaccinesantisepticsfungicidesantiviralsantibiotics, such as penicillin, which can be given to treat diseases caused by pathogens. Unfortunately, due to mutations,  antitoxinsallergensresistanceimmunitydiseaseintolerance can arise in bacteria, which makes these compounds less effective.  BacteriaFungiLysozymesProtistsToxinsViruses are also particularly hard to treat as they live inside cells, and so treatments will often harm both the pathogen and the host cells.

Drug trials can be long and expensive, and involve both preclinical trials on  cell membranesanimalsmicrobesfoetuseschildrenDNA fragments and clinical trials on humans. During clinical trials, a  painkillerphagocytequestionnairevaccineplaceboscale may be used to determine the efficacy of the medicine over and above the psychological effects of receiving treatment. Many drugs that succeed in passing the trials originally come from plants; for example,  ibuprofencardialisinsulinparacetamoldigitalispenicillin, a heart drug originating from foxgloves.