There are two main types of blood cell in the human body: white blood cells and red blood cells. These two blood cell types share common origins in the bone marrow, where all red blood cells, and most white blood cells, are produced. They also share a common distribution method. Both travel through the body suspended in a liquid called plasma that courses through the blood vessels. But differences between these two types of blood cells, and between the various subcategories of white blood cells, abound.
Function
Red blood cells serve the body by carrying oxygen. Hemoglobin, a molecule found in red blood cells, binds to oxygen in the lungs and whisks it away to muscles and organs that require it in order to function properly. Hemoglobin also binds to waste gases such as carbon dioxide. In this way red blood cells contribute to clearing the body of potentially toxic byproducts of metabolism.
White blood cells are important ammunition in the immune system's disease-fighting arsenal. There are five different types of white blood cell. Some destroy microbes by engulfing and digesting them. Others form antibodies that disrupt the ability of a virus to function, according to Gary Thibodeau, PhD, author of "The Human Body in Health and Disease."
Platelets are blood cell fragments that function as coagulators, helping in the formation of blood clots to stop bleeding.
Structure
Red blood cells have no nucleus. They are shaped like discs with concave centers on either side.
White blood cells have nuclei and come in a number of shapes and sizes. Types of white blood cell include neutrophils, eosinophils, and basophils. These are called granulocytes, meaning they contain granules within their cell bodies. Basophils contain so many granules that their presence can obscure the appearance of the nucleus.
Others white blood cells, with no granules, are called nongranulocytes. These include lymphocytes and monocytes. Monocytes are the largest type of white blood cell and have a u-shaped nucleus.
Platelets are cell fragments, according to Sheri Wick of the University of Nebraska Human Physiology and Anatomy Laboratories. They are irregularly shaped and colorless.
Lifespan
Red blood cells wear out and die over time. According to the Franklin Institute, the average life span of a red blood cell is about three months.
White blood cells vary in longevity. Some types live only briefly, dying after a few days. Others carry on for several weeks. The bone marrow and lymphatic glands continuously regenerate both types of blood cell.
References
- TThe Franklin Institute: Platelets
- The Franklin Institute: Red Blood Cells
- University of Omaha: Blood Cells
- The Human Body in Health and Disease; Gary Thibodeau, PhD and Kevin Patton, PhD; 2002
- The Merck Manuals Online Medical Library: Blood Cell Formation
