Erythrocytes

The prime function of the erythrocytes is to deliver oxygen to peripheral tissues. It is estimated that an adult man will have about 5 million erythrocytes per cubic millimeter of blood. In an adult woman, there are about 4.5 million erythrocytes per cubic millimeter. In terms of cells this is equivalent to about 82 billion erythrocytes per cubic inch of blood. Erythrocytes are homogeneous circular disks about 0.0077 millimeters in diameter that do not contain a nucleus. When viewed in great numbers, erythrocytes have the distinctly blood-red coloration. They are often referred to simply as red blood cells (RBCs).

The color of the erythrocytes is derived from a red iron-containing pigment called hemoglobin. This is a conjugated protein that consists of a globin (a protein) and a hematin (a nonprotein pigment containing iron). Hemoglobin contains 0.33% iron. When hemoglobin combines with oxygen, oxyhemoglobin is formed. When oxygen is given up to the tissues, it is then reduced back to hemoglobin. When the hemoglobin has its full complement of oxygen, it is bright red. This scarlet blood is found in the arteries which carry the blood to organ tissues throughout the body. As the oxyhemoglobin gives up oxygen, it takes on a darker crimson hue. This is found in the veins which return the blood to the lungs for reoxygenation. The erythrocytes also carry some carbon dioxide from the tissues and function to maintain a normal acid-base balance (pH) of the blood.

Once erythrocytes enter the blood, it is estimated that they have an average lifetime of about 120 days. In an average person, this indicates that about l/120th or 0.83% of the red cells are destroyed each day. The stimulus for production of new red cells is provided by erythropoietin, a hormone that is produced by the kidneys. The actual production of erythrocytes is accomplished almost entirely by the red portions of the bone marrow. Surplus red cells, needed to meet an emergency, are stored in the body mainly in the spleen. Hematocrit is the percentage of erythrocytes to total blood volume. Normal values are 42-50% (14-18 grams/100 ml blood) in males and 39-48% (12-16 grams/100 ml blood) in females.

Return to Blood Chemistry