Biconcave disk, shape

The formed elements of blood are red blood cells, platelets, and leukocytes. Red blood cells, or erythrocytes (Figure 9.2), are flexible biconcave disk-shaped bodies whose main function is to carry oxygen to tissue bound to the hemoglobin that they contain. They are generated in the marrow of various bones by the action of stem cells. The hormone erythropoietin stimulates erythrocyte production in response to tissue needs for oxygen. Marrow stem cells also produce platelets, tiny cell fragments that contain the biochemicals necessary for blood clotting. The third kind of formed elements consists of leukocytes, which are defensive white blood cells. 

Erythrocytes are small compared with most other cells and are peculiar because of their biconcave disk shape (see Fig. 1-12). They have no nucleus, because it is extruded just before the release of the cell into the blood stream from the bone marrow, where the cells develop. Their cytoplasm has no organelles and is full of the protein hemoglobin that binds 02 and C02. In the cytoplasm are other proteins also, namely, (1) the submembrane cytoskeleton, (2) enzymes of the glycolytic and... 

Normal red blood cells are deformable biconcave disks. Their shape is determined by the external environment of the cell, the metabolic activity of the cell, the nature of hemoglobin, the membrane skeleton (see below), and the age of the cell. A normal human red blood cell has a life span of about 120 days and travels a distance of about 175 miles. Much of this travel occurs in capillary channels of the microcirculation, where flow rates are very slow. Here, particularly at branch points, the shape of the cell undergoes striking deformations and can squeeze through openings as small as one-twentieth the cell diameter. Thus, the primary determinant of blood flow and viscosity is... 

Erythrocytes consist of a plasma membrane that surrounds a solution of proteins (mainly hemoglobin) and electrolytes. Mature red blood cells do not contain a nucleus. They are small, about 7-8 micrometers (pm) and shaped like a biconcave disk. Evaluation of red blood cells is important in the diagnosis and monitoring of anemia. 

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