Red blood cells (erythrocytes) are the most common type of blood cell and the body's principal means of delivering oxygen to the body tissues. In addition to this, they deliver nutrients, such as fat and carbohydrates, to the cells where they are needed to produce ATP. This is exchanged for metabolic by-products, such as lactic acid, carbon dioxide, and water; carbon dioxide is transported to the lungs where it is breathed out, water is subsequently discharged from the body through perspiration or urination, and lactic acid is taken to the liver where it is metabolized or oxidized.
Red blood cells are terminally differentiated, meaning they can never divide. Red blood cells are filled with hemoglobin (Hgb), a molecule that can bind to oxygen. In humans, red blood cells develop in bone marrow, take the form of flexible biconcave disks, lack a cell nucleus, subcellular organelles and the ability to synthesize protein, and live for about 120 days and then are ingested by phagocytic cells in the liver and spleen. Some 3 million RBCs die and are scavenged by the liver each second. The red cell is enclosed in a thin membrane that is composed of chemically complex lipids, proteins, and carbohydrates. Extraordinary distortion of the red cell occurs in its passage through minute blood vessels, many of which have a diameter less than that of the red cell. When the deforming stress is removed, the cell springs back to its original shape. The red cell easily tolerates bending and folding, but if significant stretching of the membrane occurs, the cell is damaged or destroyed. The membrane is freely permeable to water, oxygen, carbon dioxide, glucose, urea, and certain other substances, but it is impermeable to hemoglobin.
- ↑ 1.0 1.1 1.2 1.3 RCN (n.d.). Blood. RCN.com. Retrieved on 2008-10-02.
- ↑ Brookes, Douglas S. (2004). The Complete Book of Personal Training. Champaign, IL: Human Kinetics, 288-289.
- ↑ various (n.d.). Red blood cell. Wikipedia. Retrieved on 2008-10-02.
- ↑ 4.0 4.1 Revision Notes (n.d.). Composition of Blood. Revision Notes.co.uk. Retrieved on 2008-10-02.