White Blood Cells
When a foreign or infectious organism such as a virus or bacteria enters the body, white blood cells provide a primary defense mechanism that is crucial to the function of the body's immune system. There are several types of white blood cells. All of them cooperate in the defense system that protects our bodies from foreign invasion by bacteria, viruses and other potentially harmful substances. When an invader such as bacteria, a virus or other type of infection does appear, the white blood cells have a variety of ways by which they can attack. Some will produce protective antibodies that will overpower the invader. Others will surround and devour the invader.
Most white blood cells have a rather short life cycle, living from a few days to a few weeks. White cells make up only about 1 percent of blood, and, in the blood stream, there is approximately one white blood cell for every 1,000 red cells. A drop of blood can contain anywhere from 7,000 to 25,000 white blood cells at a time. If an invading infection fights back and persists, that number will significantly increase.
In the bone marrow, where all blood cells are made, there are approximately twice as many white cells as red cells. The reason for this is the very short life span of the white blood cells. Red cells spend their entire life in the blood circulation, but white cells only pass through the blood on the way to the tissues where they do their job of defense. They spend only four to six hours in the blood stream itself.
The most numerous white cells are named polymorphonuclear leukocytes, which means simply a white cell (leuko=white, cyte=cell) with multiple (poly) parts (morph). Commonly known as polys, these cells make up 60 to 70 percent of all white blood cells. Polys travel along the outer edges of the blood vessels, exiting into the tissues such as the lungs, looking for invading agents to ingest and kill. In certain kinds of bacterial infections, billions of polys are released rapidly and migrate to the site of the infection. There, the polys will begin to ingest and destroy the invading bacteria. In doing so, the polys themselves begin to disintegrate. This releases a substance that causes a special center in your brain to increase your body's temperature. The result is that body temperature and pulse increase, thereby delivering more blood and more polys to the site of the infection. This is one of the reasons you may have a "temperature" when you have a bacterial infection. Another important white cell is the lymphocyte.
Lymphocytes are produced in the bone marrow, the thymus gland, in lymph nodes and in the spleen. Unlike other types of blood cells, they have a very long life; some of them may live as long as the person. Lymphocytes are very sensitive and differentiate between the cells of the person (self) and any other type of cell (non-self), even cells from a very close relative. When a lymphocyte recognizes non-self, it cooperates with other cells in the production of antibodies (antibodies help attack and destroy foreign, or non-self, cells that may invade your body). Once an antibody reaches the invading non-self substance, it destroys the substance and both are removed from the body. Antibody production is crucial to fighting off infections and in maintaining immunity against certain diseases.
There are a number of other white blood cells that are also very important, but less numerous. Some of these include:
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Eosinophils. These are very important in fighting an allergic reaction. During the pollen season, people who are suffering the symptoms of runny nose, itchy eyes and sneezing will likely have many eosinophils.
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Basophils. These are related to polys and are also important in fighting allergic reactions.
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Monocytes. These help the lymphocytes in ingesting foreign material and in making antibodies against foreign material.
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