Red Blood Cells (Erythrocytes)
The red blood cells (RBCs), or erythrocytes, are small, biconcave, disk-shaped cells without nuclei. They contain hemoglobin (he"mo-glo'bin), a protein carrier for oxygen. Hemoglobin binds with oxygen in the cool, neutral conditions of the lungs and readily gives up oxygen under the warm, more acidic conditions of the tissues. Oxyhemoglobin (hemoglobin plus oxygen) is bright red. Deoxyhemoglobin (hemoglobin minus oxygen) is dark purple. The presence or absence of oxygen attached to hemoglobin accounts for the difference in color between arteries and veins.
The number of red blood cells in a cubic millimeter (mm3) of blood is called the red blood cell count. Males usually have 4.6 to 6.2 million cells per cubic millimeter, and females have 4.2 to 5.4 million cells per cubic millimeter. The Medical Focus reading on page 210 examines disorders resulting from abnormal red and white blood cell counts. Each cell contains about 200 million hemoglobin molecules. If this much hemoglobin were suspended within the plasma, rather than being enclosed within the cells, the blood would be so thick that the heart would have difficulty pumping it.
Red blood cells live only about 120 days and are destroyed chiefly in the liver and spleen, where they are engulfed by large phagocytic cells. When red blood cells are broken down, the hemoglobin is released and broken down into heme (hem), the iron-containing portion, and globin (glo'bin), a protein. The iron is recovered and returned to the red bone marrow for reuse. The rest of the heme undergoes further chemical degradation and is excreted by the liver in the bile as bile pigments, which are primarily responsible for the color of feces.
Red blood cells do not have nuclei but they do have hemoglobin. vvhich carries oxygen.
