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There are both nonspecific and specific defense mechanisms. The first line of defense is the skin and mucus membranes and their secretions. The skin is the first barrier that bacteria and viruses try to get through; this is impossible unless there is any kind of abrasions. Also the mucus membrane that lines the digestive, respiratory, and genitourinary tracks prevent the entry of potentially harmful microbes. The skin and mucus membrane act as a physical barrier as well as countering pathogens with a chemical defense. When we secrete saliva, tears and mucous it cleans the exposed epithelia, washing away the potential invaders.
Also, these secretions contain various antimicrobial proteins. One of these antimicrobial proteins is lysozymes, which is an enzyme that digest the cell wall of the bacteria and destroys the microbes that try to enter the upper respiratory system and around the eyes. Mucus also traps the particals it comes into contact with. When the microbes are entering the upper respiratory system the get caught and either swallowed or expelled. The trachea is lined with special epithelial cells that are equipped with cilia that sweeps the out microbes and other particals that gets trapped by the mucus. Microbes that are present in food or caught in mucus from the upper respiratory system has to pass through the acidic gastric juices produced by the stomach lining.
Phagocytosis is the ingestion of invading particles by certain types of white blood cells. This is the body main internal defense mechanism. Phagocytic cells are called neutrophils which comprise sixty to seventy percent of the white blood cells. These can destroy microbes by the chemical signals, neutrophils can leave the blood and enter infected tissue by amoeboid movement. The neurophils can only live a few days because they are self-destructive as well as destroying the foreign invaders. Another five percent of the white blood cells are made up of monocytes which provide phagocytic defense. Once matured the monocytes circulate inside the blood for a few hours, then they migrate into the tissue where they grow in size and develop into macrophages. Macrophages are the largest phagocytes cells they are especially effective and having long life as phagocytes. There are also natural killer cells which do not attack the microorganisms directly, but they destroy the body’s own infectious cells. These killers also attack the cells that could form tumors.
There is a group of at least twenty proteins act as the complement system, which acts in cooperation with other defense mechanisms. These proteins act as a group in activation steps that culminate with lysis of the invading microbes. Also there are interferons, which are chemical messengers of the immune system, that are produced by virus-infected cells, and capable of helping other cells resist the virus. There are three types of interferons-alpha, beta and gamma.
The inflammatory response is when tissue reacts to physical injury, like a cut. When an injury occurs the small blood vessels in the area dilate, as well as increase the blood supply to the area. The swollen blood vessels are more preamble the fluid moves from the blood to neighboring tissue, which causes edema. The most important element of the inflammatory response is the phagocyte migration from the blood to the injured tissues.
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