The body has specific and non-specific defence mechanisms.Specific defence mechanisms involve white blood cells called B-lymphocytes and T-lymphocytes.Non-specific defence mechanisms involve white blood cells called phagocytes and a range of other defence mechanisms.There are physical and chemical barriers to the entry of pathogens.Physical barriersThe skin prevents the entry of pathogens. It has a skin flora of healthy microorganisms that outcompete the pathogens.Many of the body tracts are lined with mucous membranes. Sticky mucus traps microorganisms and contains phagocytes and lysozymes that destroy bacteria and fungi.Coughs and sneezes, diarrhoea and vomiting expel pathogens from the body.Blood Clotting.The blood clots rapidly to seal a wound so pathogens do not enter the body. When platelets come into contact with collagen in the skin or the walls of damaged blood vessels they stick to it and begin secreting thromboplastin which starts a clotting cascade and serotonin which constricts smooth muscle.The clot dries into a hard, tough scab. Epidermal cells below the scab grow and damaged blood vessels regrow.Inflammatory responseInflammation is a localised response to pathogens.Mast cells are activated and secrete histamines and cytokines. Histamines make blood vessels dilate causing localised heat and redness. Histamines make capillaries leaky so blood plasma is forced out as tissue fluid.Cytokines attract white blood cells (phagocytes) to the site of infection.Fever.Cytokines stimulate the hypothalamus to reset the body's set point and the body temperature goes up from 37°C.Most pathogens reproduce best at 37°C so higher temperatures inhibit pathogen reproduction. The specific immune system works better at higher temperatures.