White Blood Cells

Without white blood cells (WBCs), or leukocytes, we would be defenseless against sickness and disease. These cells play a critical role in the immune system, fighting off the viruses, bacteria, toxins, and other foreign organisms that regularly invade our bodies.

Like guards on patrol, WBCs float through the bloodstream until they receive a chemical message from an area of tissue that requires protection. They then pass through the blood vessels to destroy the harmful organisms. Most WBCs live for only a few days.

Because of this short life cycle, people produce about 100 billion WBCs a day. Grown in the bone marrow, the soft tissue found inside the bone, they develop into one of five major types that vary by size, shape, and function. For example, basophils secrete markers to signal the area of infection, while eosinophils, lymphocytes, and neutrophils attack the invading parasite, bacterium, fungus, or virus. Monocytes act as the body’s cleanup crew, devouring bacteria and dead or damaged cells.

In medicine, physicians count WBCs as a way to detect disease and monitor recovery from illness. The standard scientific measure is the number of cells per microliter of blood; a healthy adult has 4,500 to 10,000 WBCs per microliter. A low WBC count, or leucopenia, is usually caused by a bone marrow disorder and raises the risk of infection. A high WBC count, or leukocytosis, is often the result of the body fighting off an infection. But a consistently elevated number may signal an underlying problems of the immune system, such as allergies, arthritis, or leukemia, a cancer of the blood.

Additional Facts

1. The word leukocyte is derived from the Greek leukos (“white”) and cytes (“cells”).
2. WBCs make up only about 1 percent of your blood; the majority consist of red blood cells and plasma.
3. A French professor of medicine, Gabriel Andral (1797-1876), and an English physician, William Addison (1802-1881), separately reported the first descriptions of WBCs in 1843, more than 200 years after the discovery of red blood cells.

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