Body Defenses Against Disease (1978)

[Music] what would it be like to live your entire life in a space suit separated from the World by barrier of cloth and plastic David has lived his entire life in a sterile room or in this special suit isolated from the millions of germs that we encounter every day the air he breathes the food he eats everything he touches must be sterilized because David's body has no way of fighting disease his space suit is a life-saving barrier protecting him from the dangerous world of germs outside fortunately most of us don't need this kind of isolation because our bodies have immunity the inborn ability to resist harmful germs even before birth the body begins to develop the capacity to fight diseases throughout life we are exposed to a great variety of germs that can make us sick with a microscope we can see many of these germs bacteria are one type of germ that cause disease these bacteria live in the human intestinal tract under some conditions they can make a sick other kinds of germs include microscopic animals such as this parasite certain funi or molds can also make us sick to see other kinds of germs we use an electron microscope this microscope can magnify objects hundreds of thousands of times making it possible to see extremely small germs called viruses viruses can only reproduce and grow within living cells these viruses magnified 150,000 times are responsible for the crippling disease polio this virus causes measles this this is one of the many forms of the virus that causes flu or influenza we are constantly in contact with germs in the air around us and in the food we eat and water we drink so why aren't we sick all the time most of the time we stay well because the body has a number of ways of fighting germs using animation and photography through the microscope we can observe some of the ways the body defends itself against disease many germs enter the body through natural openings such as the mouth and nose here they encounter an immediate barrier a sticky layer of mucus that is kept in constant motion by tiny hairlike structures called cyia as germs become trapped in this mucus layer the rhythmic beating of cyia moves them to the back of the throat where they are swallowed farther along in the breathing passages other Celia sweep germs and foreign substances up and away from the lungs germs that are swallowed move down into the stomach where powerful digestive enzymes and strong acid destroy most of [Music] them another of the bod's barriers to infection is the skin human skin appears to be a smooth even surface until it is viewed with the electron microscope here is a section of human skin magnified 100 times this section of skin is magnified 2,000 times it reveals a rough scaly surface upon which large numbers of germs accumulate germs that come in contact with our skin rarely penetrate surface because of many layers of tightly compacted cells but when the surface of the skin is broken germs enter the body blood flowing into the wound begins to coagulate trapping germs and localizing the infection blood plays a critical role in our immunity to disease at the wound specialized cells called phagocytes that travel in the bloodstream immediately begin the process of destroying germs here we see fago sites engulfing living [Music] bacteria germs that are not trapped or destroyed near a wound may enter the body's circulatory system in the bloodstream germs pose a serious threat to all parts of the body to meet this Threat all of the body's defenses are called into play as germs circulate in the blood they move into the body tissues and then into the lymphatic system lymph is a fluid that surrounds many of the body's cells the lymphatic system plays a major role in the body's defense against disease within this system are structures called lymph nodes the lymph nodes help to trap and Destroy germs this occurs in several ways some germs are devoured by large fago sites other cells in the lymph nodes called lymphocytes recognize invading germs when they come into contact with a germ these lymphocytes are activated and begin to divide forming additional lymphocytes these newly formed lymphocytes start to manufacture special proteins called antibodies antibodies help to destroy germs although incredibly small antibodies can be photographed with an electron microscope here we see antibodies magnified more than 450,000 times revealing their characteristic y-shape when a germ enters the body it triggers the production of one particular kind of antibodies these antibodies fit that type of germ and no other for example antibodies that fight typhoid germs will not protect you against pneumonia the antibodies attached to the cell wall of the germ this begins a process that leads to the rupture and destruction of The Germ here we see bacteria to which antibodies have been added we can't see the antibodies themselves but we can observe their effect on the germs another way in which antibodies combat germs is to bring them together in groups or clumps these bacteria cause a form of dissenter more commonly known as diarrhea when a drop of solution containing antibodies is added to the slide almost immediately the germs clump together clumping makes it easier for fago sites to locate and consume germs