Life Cycle of the Rbc

Lisa Nizam

The Life Cycle of the Red Blood Cell

Red blood cells (RBCs), also known as erythrocytes make up ninety-nine percent of our formed elements (erythrocytes, leukocytes, and thrombocytes) in the blood, but only account for less than fifty percent of our total blood volume which includes plasma, the fluid portion of our blood. Erythrocytes are specialized cells with the important job of transporting oxygen in the blood. Several factors help with this job. Their structure and chemical composition make them very efficient. They appear red due to a chemical known as hemoglobin. Hemoglobin is also responsible for the transportation of oxygen due to heme, an iron ion that attracts oxygen. Although, erythrocytes only live for about one hundred and twenty days in circulation, they are produced in the bone marrow at an astonishing rate of two million per second in a process known as erthyropoiesis. This is necessary in order to maintain homeostasis and prevent hypoxia, as mature RBCs are anucleic (lack a nucleus) and have a limited ability to repair themselves. They lack organelles and have no mitochondria, so are not true cells. Production of new RBCs involves several stages, beginning with hemocytoblasts to maturity, where they enter the blood stream. The number one factor that stimulates the production of new RBCs is a condition known as hypoxia, a reduction of available oxygen. This stimulates erythropoietin (EPO) to initiate RBC production. In addition, erythropoiesis cannot occur normally if the bone marrow is lacking vitamins like B12 and others. Finally, barring some type of damage, these cells begin to degenerate due to aging. Most effete RBCs are removed from circulation before they hemolyze, or rupture. The process of removal involves macrophages in the liver, spleen, and lymph nodes. Some of the components of the old RBC’s are recycled into amino acids and iron, while others are converted and removed from the body: biliverdin, bilirubin, stercobilin...