erythrocyte /erith″rəsīt′/ [Gk, erythros + kytos, cell] , mature red blood cell; a biconcave disk about 7 μm in diameter that contains hemoglobin confined within a lipoid membrane. It is the major cellular element of the circulating blood and transports oxygen as its principal function. The number of red blood cells per microliter of blood is 4.5 to 5.5 million in men and 4.2 to 4.8 million in women. The red blood cell count varies with age, activity, and environmental conditions. An erythrocyte normally survives for 110 to 120 days, when it is removed from the bloodstream and broken down by the reticuloendothelial system. New erythrocytes are produced at a rate of slightly more than 1% a day; thus a constant level is usually maintained. Acute blood loss, hemolytic anemia, or chronic oxygen deprivation may cause erythrocyte production to increase greatly. Erythrocytes originate in the marrow of the flat bones or at the end of long bones. Also called red cell, red corpuscle. Compare normoblast, reticulocyte. See also erythropoiesis, hemoglobin, red cell indexes.
