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YOUR IMMUNE SYSTEM
Basics of the Immune System
Let's start at the beginning. What does it mean when someone says "I feel sick today?" What is a disease? By understanding the different kinds of diseases it is possible to see what types of disease the immune system helps you handle.
When you "get sick", your body is not able to work properly or at its full potential. There are many different ways for you to get sick -- here are some of them:
Mechanical damage - If you break a bone or tear a ligament you will be "sick" (your body will not be able to perform at its full potential). The cause of the problem is something that is easy to understand and visible.
Vitamin or mineral deficiency <http://science.howstuffworks.com/food5.htm> - If you do not get enough vitamin D your body is not able to metabolize calcium properly and you get a disease known as rickets. People with rickets have weak bones (they break easily) and deformities because the bones do not grow properly. If you do not get enough vitamin C you get scurvy, which causes swollen and bleeding gums, swollen joints and bruising. If you do not get enough iron you get anemia, and so on.
Organ degradation - In some cases an organ is damaged or weakened. For example, one form of "heart disease" is caused by obstructions in the blood <http://science.howstuffworks.com/blood.htm> vessels leading to the heart muscle, so that the heart does not get enough blood. One form of "liver disease", known as Cirrhosis, is caused by damage to liver cells (drinking too much alcohol is one cause).
Genetic disease - A genetic disease is caused by a coding error in the DNA. The coding error causes too much or too little of certain proteins to be made, and that causes problems at the cellular level. For example, albinism is caused by a lack of an enzyme called tyrosinase. That missing enzyme means that the body cannot manufacture melanin, the natural pigment that causes hair color, eye color and tanning. Because of the lack of melanin, people with this genetic problem are extremely sensitive to the UV rays in sunlight.
Cancer - Occasionally a cell will change in a way that causes it to reproduce uncontrollably. For example, when cells in the skin called melanocytes are damaged by ultraviolet radiation in sunlight they change in a characteristic way into a cancerous form of cell. The visible cancer <http://science.howstuffworks.com/cancer.htm> that appears as a tumor on the skin is called melanoma. (See How Sun Tans and Sunburns Work <http://science.howstuffworks.com/sunscreen.htm> for more information.)
Seeing Your Immune System
Your immune system works around the clock in thousands of different ways, but it does its work largely unnoticed. One thing that causes us to really notice our immune system is when it fails for some reason. We also notice it when it does something that has a side effect we can see or feel. Here are several examples:
When you get a cut, all sorts of bacteria and viruses <http://science.howstuffworks.com/virus-human.htm> enter your body through the break in the skin. When you get a splinter you also have the sliver of wood as a foreign object inside your body. Your immune system responds and eliminates the invaders while the skin heals itself and seals the puncture. In rare cases the immune system misses something and the cut gets infected. It gets inflamed and will often fill with pus. Inflammation and pus are both side-effects of the immune system doing its job.
When a mosquito <http://science.howstuffworks.com/mosquito.htm> bites you, you get a red, itchy bump. That too is a visible sign of your immune system at work.
Each day you inhale thousands of germs (bacteria and viruses) that are floating in the air. Your immune system deals with all of them without a problem. Occasionally a germ gets past the immune system and you catch a cold, get the flu or worse. A cold or flu is a visible sign that your immune system failed to stop the germ. The fact that you get over the cold or flu is a visible sign that your immune system was able to eliminate the invader after learning about it. If your immune system did nothing, you would never get over a cold or anything else.
Each day you also eat hundreds of germs, and again most of these die in the saliva or the acid of the stomach. Occasionally, however, one gets through and causes food poisoning. There is normally a very visible effect of this breach of the immune system: vomiting and diarrhea are two of the most common symptoms.
An immune cell undergoing an allergic reaction
There are also all kinds of human ailments that are caused by the immune system working in unexpected or incorrect ways that cause problems. For example, some people have allergies <http://science.howstuffworks.com/allergy.htm>. Allergies are really just the immune system overreacting to certain stimuli that other people don't react to at all. Some people have diabetes <http://science.howstuffworks.com/diabetes.htm>, which is caused by the immune system inappropriately attacking cells in the pancreas and destroying them. Some people have rheumatoid arthritis, which is caused by the immune system acting inappropriately in the joints. In many different diseases, the cause is actually an immune system error.
Finally, we sometimes see the immune system because it prevents us from doing things that would be otherwise beneficial. For example, organ transplants <http://science.howstuffworks.com/organ-transplant.htm> are much harder than they should be because the immune system often rejects the transplanted organ.
Viral or Bacterial Infection
When a virus or bacteria (also known generically as a germ) invades your body and reproduces, it normally causes problems. Generally the germ's presence produces some side effect that makes you sick. For example, the strep throat bacteria (Streptococcus) releases a toxin that causes inflammation in your throat. The polio virus releases toxins that destroy nerve cells (often leading to paralysis). Some bacteria are benign or beneficial (for example, we all have millions of bacteria in our intestines and they help digest food), but many are harmful once they get into the body or the bloodstream.
Viral and bacterial infections are by far the most common causes of illness for most people. They cause things like colds, influenza, measles, mumps, malaria, AIDS and so on.
The job of your immune system is to protect your body from these infections. The immune system protects you in three different ways:
It creates a barrier that prevents bacteria and viruses from entering your body.
If a bacteria or virus does get into the body, the immune system tries to detect and eliminate it before it can make itself at home and reproduce.
If the virus or bacteria is able to reproduce and start causing problems, your immune system is in charge of eliminating it.
The immune system also has several other important jobs. For example, your immune system can detect cancer in early stages and eliminate it in many cases.
Bacteria and Viruses Your body is a multi-cellular organism made up of perhaps 100 trillion cells. The cells in your body are fairly complicated machines. Each one has a nucleus, energy production equipment, etc. Bacteria are single-celled organisms that are much simpler. For example, they have no nucleus. They are perhaps 1/100th the size of a human cell and might measure 1 micrometer long. Bacteria are completely independent organisms able to eat and reproduce - they are sort of like fish swimming in the ocean of your body. Under the right conditions bacteria reproduce very quickly: One bacteria divides into two separate bacteria perhaps once every 20 or 30 minutes. At that rate, one bacteria can become millions in just a few hours. A virus is a different breed altogether. A virus is not really alive. A virus particle is nothing but a fragment of DNA in a protective coat. The virus comes in contact with a cell, attaches itself to the cell wall and injects its DNA (and perhaps a few enzymes) into the cell. The DNA uses the machinery inside the living cell to reproduce new virus particles. Eventually the hijacked cell dies and bursts, freeing the new virus particles; or the viral particles may bud off of the cell so it remains alive. In either case, the cell is a factory for the virus.
Source:http://science.howstuffworks.com/immune-system2.htm
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Canapril
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