The normal life span of an erythrocyte is 120 days. In order for the blood to perform to its optimum, new batch of red blood cells are supplied every day. The process of making red blood cells is truly magnificent in its own rights.
Hematopoiesis is the term used when referring to the formation of blood cells. It comes from the word hemato which means blood and poiesis which means to make. This process happens in the bone marrow, specifically the red bone marrow.
The red bone marrow is composed of a network of reticular connective tissue. It borders on blood capillaries called blood sinusoids. A variety of cells are found within this network, which includes macrophages, reticular cells, fat cells and immature blood cells. The production of each type of blood cell involves a dynamic process which is largely dependent on the needs of the body and some regulatory factors. When the newly formed cells are mature enough, they move through the thin walls of the sinusoids, awaiting their chance to enter the bloodstream. On average, the red bone marrow makes about an ounce of new blood which contains almost 100 billion new cells, everyday.
The Stem Cell
Although the different types of formed elements or blood components have dissimilar roles and functions, a similarity exist in their life histories. All of the formed elements arise from the same type of stem cell called the pleuripotent hematopoietic stem cell or what is also referred to as hemocytoblast. This type of specific stem cell is found in the red bone marrow. However, once a cell is committed to a specific blood cell pathway, it is no longer able to change. A cell is said to have chosen a specific blood cell path when surface membrane receptors start to appear. These membrane surface receptors then respond to growth factors or specific hormones which influences the cell towards the chosen specialization.
The process of producing new erythrocyte is termed erythropoiesis. This process is stared when a myeloid stem cell changes to proerythroblast. The presence of proerythroblast gives rise to basophilic erythroblasts that functions to produce enormous amounts of ribosomes. During this process, hemoglobin synthesis and accumulation of iron occurs as the young erythroblast is transforming to become a late erythroblast then finally becoming a normoblast. At first the new cell being produces appears bluish, but as the transformation happens, the color changes to a pinkish shade because of the presence of hemoglobin. To give way to more hemoglobin, the normoblast ejects most of its organelles. At this point, the nucleus has done its role. It degenerates and then gets ejected. The part where the nucleus used to be located is now vacant, the cell collapses on that spot giving rise to the distinct biconcave shape.
The resulting cell, after undergoing all the processes, is called a reticulocyte. It is named as reticulocyte because it still has traces of scant reticulum of clumped ribosomes. The entire process takes roughly 15 days to complete. The reticulocytes then enter the bloodstream, where it will mature in two days and assumes its role as transport vehicle.