Red Blood Cells (erythrocytes) are responsible for delivering oxygen (via hemoglobin) to body cells and returning carbon dioxide to the lungs. They are the most numerous cell type in the blood. RBC live about 120 days and then are ingested by phagocytosis in the liver and spleen. Iron in the hemoglobin is reused. Heme in the RBC is turned into bile pigments and excreted by the liver, we know this as the brown color of feces. Millions of RBCs naturally wear out and are scavenged by the liver each second. The process of replacing RBC is called Reticulocytosis. A normal dog will have about 5.5 million RBC.
