Nita Rainey The first line of defense is the external barriers of the body such as the skin. The skin is used as an external barrier. The first line of defense deals with both physical and chemical barriers. These barriers help with preventing infection. Some examples of prevention methods of external barriers may include, the skin, tears, mucus, cilia, stomach acid, and urine flow. The skin is the largest organ of the body. The skin helps protect against pathogens and any foreign substances. Which is why it is categorized as a form of mechanical protection. The skin is made up of keratinized cells. The skin is waterproof barrier that helps out any foreign substance from coming into the body. This barrier works very effectively unless the barrier is broken, examples of this are: digestive openings, reproductive openings. Respiratory opening, sensory organs. Another mechanical from of protection is the secretion of mucus byway of the windpipes cilia and mucus. The cilia and mucus help move microbes or particles toward the throat and away from the lungs. For example, if there is smoke or dust in the air the cilia and mucus work as a sweeper to remove the particles away from your lungs. Another good example of the external barrier working to wash of remove any particles or pathogens is through tears, urine, and saliva. The entry/exit points that they use are the eyes, nose, mouth and bladder. Tears and saliva both contain enzymes that assist in breaking down any foreign bacteria. If the bacteria is not destroyed it then becomes trapped in the mucus. The urine flow empties your bladder to help flush out any pathogens. Which why is considered to be a friendly bacteria. Chemical protection is the other method used by the external ba... ... middle of paper ... ...oreign bacteria and let the team of cells that I just talked about above know that there is an intruder aboard, so they need to search and destroy. Which is why during an infection it is common to see the neck, groin, or armpit swollen indicating an infection. The third defense is specific response. This defense involves immunity that the body has already developed against a specific foreign pathogen, such a virus or pet dander. This defense steps in when the second response is unable to take of the infection and it beginning to spread out. The third response uses the same cells such as Macrophages, Helper T cells, Cytotoxic T cells, and B cells. In addition to those cells specific response also uses effector cells and memory cells. Effector cells search and destroy foreign pathogens. Memory cells lay inactive and become activated me that specific invader returns.