The immune system is the body's overall defense system against harmful invaders, from the outside world, capable of entering the body in one way or another. The immune system is not one or two organs that do all the work, but rather a network of parts throughout the body that work with other body systems to fight viruses, diseases, infections, and anything else that the immune system knows it doesn't belong. in the body. Say no to plagiarism. Get a Custom Essay on “Why Violent Video Games Should Not Be Banned”?Get Original Essay A pathogen is any organism or virus that can cause disease after entering the body. The first line of defense against pathogens lies in external barriers such as the skin. The nose has nostril hairs which act as a filter for elements entering the body through the nose. The nose can also fill with mucus which can exit the body to eliminate any pathogens that may enter the nostrils. The eyes have cilia that can chase away pathogens when a person blinks. The average person blinks about 16 times per minute. This is usually enough to keep pathogens floating in the nearby air out. According to Campbell Essential Biology with Physiology 4th edition (2012): External barriers also include chemical defenses in the form of antimicrobial secretions. Sweat, saliva and tears contain enzymes that disrupt bacterial cell walls. The glands produce oils and acids that make the skin inhospitable to many microbes. Concentrated stomach acid kills most of the bacteria we swallow before they can enter the bloodstream. (p. 518) External barriers are the first line of defense. When a pathogen manages to cross the barriers, it is now up to the internal immune system to fight it. This is the second line of defense. Phagocytic cells are white blood cells capable of consuming foreign cells or pathogens, thereby killing them. Another type of white blood cell that can kill pathogens or infected cells are NK cells, or natural killer cells. These NK cells release chemicals that kill infected cells. The body has another natural defense, namely defensive proteins. When a virus successfully infects a cell, it can release interferon molecules. These interferon molecules bind to nearby healthy cells. The binding of interferon molecules to healthy cells encourages them to produce antiviral proteins. Other natural defensive proteins created by our immune system are complement proteins, which directly attack pathogens. (Simon, 2012, p. 519) The lymphatic system is a system of vessels and numerous lymph nodes packed into white blood cells. Other organs of the lymphatic system include the tonsils, thymus, and spleen. “The two main functions of the lymphatic system are to return tissue fluid to the circulatory system and to fight infections. » (Simon, 2012, p. 520) The lymphatic system works in conjunction with the circulatory system. For example, when a person cuts paper from a dollar bill, the dollar bill introduces bacteria into and under the skin. The first line of defense has already been crossed. The lymphatic system senses chemical signals that the skin has been torn, then sends white blood cells through the.