Red Blood Cells

1. Red blood cells (RBCs), also known as erythrocytes, are the most numerous type of cellular component of blood (Kimball, 2004). Women have on average 4.8 million per cubic millimeter, and men have an average of 5.4 per cubic millimeter. Erythrocytes manufacture and store hemoglobin, the oxygen-carrying pigment they contain, which gives them their red color when it is bound to oxygen, making arterial blood bright red. The hemoglobin in red cells picks up oxygen in the lungs and transports it to the tissues of the body, exchanging it for carbon dioxide which it transports back to the lungs to be exhaled. Deoxygenated blood appears bluish (venous blood). Erythrocytes manufacture hemoglobin until it occupies roughly 90 percent of the dry weight of the cells, and the nucleus is squeezed out of the cells. Erythrocytes are terminally differentiated, i.e. they can no longer divide. Their lifespan in the blood is about 120 days, and after this time, they are ingested by phagocytes in the liver and spleen. Most of the iron from the hemoglobin in these cells is recycled. The remaining heme portion of the hemoglobin molecules is degraded to bile pigments and excreted by the liver. Roughly three million RBCs die and are scavenged by the liver every second.

White blood cells, the other major cellular component of blood are much less numerous than red blood cells and exist in a ratio of 1:700 to red cells (Kimball, 2004). These cells are nucleated, help protect the body from

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