The adult human circulatory system contains between 20 and 30 trillion red blood cells (RBCs), the precise size and number of which can vary from person to person. Some people may have fewer, but larger RBCs, while others may have a larger number of smaller RBCs. Although these differences in size and number may seem inconsequential, they raise an important question: Just what controls these characteristics of RBCs? This question is particularly relevant for the roughly one-quarter of the population that suffers from anemia, which is often caused by flawed RBC production. A better understanding of how RBC production is controlled may offer greater insight into the development and potential treatment of anemia.
