What Are Red Blood Cells?

Red blood cells (RBCs) have the responsibility of transporting oxygen throughout the body. About 33 percent of the weight of an RBC is attributed to a specialized protein called hemoglobin and thus RBCs are often referred to as “bags of hemoglobin.” Hemoglobin is a large and complex 

protein that contains four atoms of iron. Hemoglobin’s job is to bind to oxygen so that it can be transported in the blood. There are about 42 to 52 million RBCs per milliliter (or cc) of blood; and each RBC contains about 250 million hemoglobin molecules. Since each hemoglobin molecule can carry four oxygen molecules, the potential exists to transport one billion molecules of oxygen in each RBC.
 

There are two reasons for the need for such a large amount of hemoglobin in our blood. First, oxygen does not dissolve very well into our blood. Second, the demand for oxygen is extremely high in our body. Therefore, hemoglobin increases the ability of the blood to carry oxygen tremendously. Any situation that significantly decreases either the number of RBCs or the level of hemoglobin they carry can compromise oxygen delivery to our tissues and potentially compromise function and health.