"Blood components & description. 7-8% of human body weight. Transports oxygen and nutrients to our cells and gets rid of carbon dioxide and other waste products, it plays a vital role in our immune system and maintains a constant body temperature. Four of the most important components are red cells, white cells, platelets, and plasma. All humans produce these blood components--there are no populational or regional differences.
Red Cells
Human erythrocytes
Red cells, or erythrocytes , are relatively large microscopic cells without nuclei. Red cells make up 40-50% of the total blood volume. The red cells are produced continuously in our bone marrow from stem cells. Hemoglobin is the gas transporting protein molecule that makes up 95% of a red cell. Each red cell has about 270,000,000 iron-rich hemoglobin molecules. People who are anemic generally have a deficiency in red cells.
White Cells
White cells, or leukocytes , exist in variable numbers and types but make up a very small part of blood's volume--only about 1%. Most are produced in our bone marrow from the same kind of stem cells that produce red cells. Some white cells (called lymphocytes ) are a major part of the immune system. Other white cells (called granulocytes and macrophages ) protect our bodies from infection by surrounding and destroying bacteria, viruses, fungi, or other parasites. They also have the function of getting rid of old, unneeded blood cells as well as foreign matter such as dust and asbestos. The red cells remain viable for only about 120 days before they are removed from the blood and their components recycled in the spleen. Individual white cells usually only last 18-36 hours before they also are removed.
Platelets
Platelets , or thrombocytes , are cells that clot blood at the site of wounds. They do this by adhering to the walls of blood vessels, thereby plugging the rupture in the vascular wall. They also can release coagulating chemicals which cause clots to form in the blood that can plug up narrowed blood vessels. There are more than a dozen types of blood clotting factors and platelets that need to interact in the blood clotting process. Recent research has shown that platelets help fight infections by releasing proteins that kill invading bacteria and some other microorganisms. In addition, platelets stimulate the immune system. Individual platelets are about 1/3 the size of red cells. They have a lifespan of 9-10 days. Like the red and white blood cells, platelets are produced in bone marrow from stem cells.
Plasma
Plasma is the relatively clear liquid protein and salt solution which carries the red cells, white cells, and platelets. Normally, 55% of our blood's volume is made up of plasma. About 95% of it consists of water. Plasma circulates metabolism waste, blood clotting factors, sugars, lipids, vitamins, minerals, hormones, enzymes, antibodies, and other proteins. It is likely that plasma contains some of every protein produced by the body--approximately 500 have been identified in human plasma so far.
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