Answer
The developing red blood cell released from the bone marrow is called a reticulocyte. It completes its maturation in the blood plasma where it becomes an erythrocyte.
Work Step by Step
In the process erythropoiesis some electhrocyte colony forming units (ECFU) are stimulated by the hormone erythropoietin to develop proerythroblasts. Proerythroblasts transform to erythroblasts which divide to form many cells. An important role of erythroblasts is to synthesize hemoglobin, the oxygen carrying pigment of red blood cells. After an erythroblast has made enough hemoglobin it dispenses with its nucleus and becomes an enucleate entity called a reticulocyte. The reticulocyte leaves the bone marrow at this point and continues its maturation in the blood plasma. As maturation proceeds a reticulocyte loses its polyribosomes. It is considered a mature erythrocyte when it has lost all its ribosome --in addition to having lost its nucleus earlier in development The mature erythrocyte is sometimes described as an enucleate biconcave disc. It can fold to navigate small diameter capillaries , but as it gets older and its proteins become fragile, the RBC is unable to make new proteins having lost its nucleus and protein synthetic machinery. Erythrocytes live for about 120 days.
