Red Blood Cells are the most common type of blood cells. Also known as the RBC's or enthrocytes principal means of delivering oxygen from the lungs to body tissues in a human body. A single drop blood contains millions of red blood cells which are constantly traveling through your body delivering oxygen and removing wastes. The absence of the red blood cells in our body would mean that you are virtually non-existent as you would surely die of suffocation.

Red blood cells are red because they contain a protein called hemoglobin that is bright red in color. As the blood passes through the body's tissue, the hemoglobin releases the oxygen to the cells. The empty hemoglobin molecules then bond with the tissue's carbon dioxide or other waste gases, transporting it away. The Red blood cells develop in about 7 days and live a total of about 120 days and eventually die as they get worn out. The bones in a human body actually produce the RBC's. Even though the blood is circulated in our body, it is not made all the time.

Structure of small red blood cells

The diameter of a typical human erythrocyte disk is 6-8 m, much smaller than most other human cells, a typical erythrocyte contains about 270 million hemoglobin molecules, with each carrying four heme groups. Adult humans have roughly 2-3 1013 red blood cells at any given time (women have about 4 million to 5 million erythrocytes per cubic millimeter (micro liter) of blood and men about 5 million to 6 million; The red blood cells store collectively about 3.5 grams of iron, more than five times the iron stored by all the other tissues combined. The process by which red blood cells are produced is called erythropoiesis. Erythrocytes are continuously being produced in the red bone marrow of large bones. The aging cells swell up to a sphere-like shape and are engulfed by phagocytes, destroyed and their materials are released into the blood. The main sites of destruction are the liver and the spleen. The heme constituent of hemoglobin is eventually excreted as bilirubin.

The blood types of humans are due to variations in surface glycoprotein of erythrocytes. Since human body is continuously making more blood, it is safe for healthy adults to donate blood. The blood is then stored for emergency situations. Initially after giving the blood, the donor may feel some momentary light headedness due to the loss of the oxygen rich red blood cells and blood sugar. But the body quickly stabilizes itself.