Your body has a two line defense system against pathogens (germs) that make you sick. Pathogens includes bacteria, viruses, toxins parasites and fungi. The first line of defense (or outside defense system) includes physical and chemical barriers that are always ready and prepared to defend the body from infection. These includes your skin, tears, mucus, cilia, stomach acid, urine flow, 'friendly' bacteria and white blood cells.
Phatogenic (disease causing microorganism) must make it pass first the first line defense. If the first line defense is broken, the second line defense of your body is activated. The microorganisms that live all over your skin can't get through your body unless it's broken.
Tears, Mucus and Saliva- Yours ears, nose and eyes are obvious entry points of pathogens. Tears, mucus and saliva contains an enzyme that breaks down the cell wall of many bacteria. Those that are not killed immediately are trapped in mucus and swallowed.
Cilia- very fine hairs (cilia) lining your windpipe move mucus and trapped particles away from your lungs. Particles may be bacteria, particles such as dusts or smoke.
Stomach acid- kills bacteria and parasites that have been swallowed.
Urine flow- flushes out pathogens in bladder area.
Friendly beneficial bacteria- stops other harmful bacteria from taking over.
Neutrophils- white blood cells that can find, kill and ingest pathogens seeking the entrance into the body.
in short first line of defense is shown by skin which prevent us from infection 'as the upperlayer of skin is brusted or burn than a watery substance or an colourless liquid comes out due to death of cells and some where due to pressure .as the injury site is open for entry of microorganisms which may cause secondary infection.our body release chemical substance to kill the microorganism(an fighting between antigen and antibody starts).likeways neutophils or whiteblood cells/carps show phagosystmic function