The Immune System
Introduction
The immune system is the body's defense mechanism. Its job is to prevent attacks by invaders that do not belong in the body, and kill those invaders which do get into the body. This prevents and fights infections and other diseases.
- First, the body prevents infection by "keeping out" invaders using physical barriers such as skin. This first line of defense is called anatomic barriers. These barriers are made of epithelial cells. This type of immunity is called natural immunity, and humans are born with it.
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Bodily invaders are called antigens. An antigen is any substance that activates the body's immune fighters, special white blood cells called lymphocytes. These activated lymphocytes have specific functions:
- Some cells are activated in the bone marrow. These cells are called B cells. B cells create antibodies to help destroy antigens.
- Some cells are activated in the thymus. These cells are called T cells, and they have several functions. Some actually have a "memory." They both destroy infected cells and "remember" the antigen for fast action if it meets it again. Others become "helper" cells to assist in activating B cells and another type of cell called phagocytes.
- Phagocytes identify antigens to other lymphocytes and destroy them by surrounding and "digesting" them (a process known as phagocytosis).
- Natural killer cells destroy tumor cells and virus cells.
- All lymphocytes are part of the body's acquired immunity, that is, immunity that the body does not have until it is exposed to antigens and T cells "remember" it for further use.
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Some examples of antigens are:
- Bacteria: living, single-cell microorganisms which can muliply by splitting in half.
- Viruses: infectious substances which are not complete organisms. Lacking some genetic material, a virus needs a "host cell" to reproduce, and multiplies after it has "stolen" genetic material from its host cell, destroying the host in the process.
- Allergens: substances which, when breathed in, cause an over-sensitive response. Examples include pollen, dust mites, and cigarette smoke.
Free radicals and antioxidants
- Free radicals are unstable substances which “attack” cells in an attempt to steal an electron and become stable. This process damages the delicate cell membrane and makes the cells targets for cancer and other diseases. This process is called oxidation.
- When free radicals attack cells, they damage the delicate cell membrane. When this happens to a bodily invader, it’s good. However, free radicals also attack healthy body cells.
- Free radicals are the result of the normal metabolic (energy producing) process. Our bodies create even more of them when we exercise or are exposed to poisonous substances such as cigarette smoke and pollution.
- Free radicals are blamed for a wide range of diseases from cancer and coronary heart disease, to a progressive eye disease which causes blindness. The cell damage they cause also contributes to the normal aging process.
- Antioxidants prevent this attack and cell damage by “donating” an electron to free radicals to neutralize them.
The common cold? Hardly
- Runny nose, cough, and fever-these are all symptoms that people associate with a “cold.” But often when someone says they have a cold, they have something entirely different.
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Colds are caused by viruses and produce very specific symptoms:
- Runny nose (first, clear; later, thicker and slightly colored - a more pronounced, greenish color signifies a bacterial infection, not a cold).
- Sneezing
- Slight fever(a high fever may indicate something more severe)
- Decreased appetite
- Red eyes
- Sore throat
- Cough
- Lethargy
- Other problems may cause similar symptoms, however. For example, allergies may produce a runny nose, red eyes, and sneezing - but no fever. Influenza, a more severe viral infection, produces similar symptoms but, with a higher fever. Some bacterial infections may also produce similar symptoms, with characteristically higher fevers and thicker, greenish discharges.
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