In general, the production of red blood cells is controlled by erythropoietin, a hormone produced and released by the kidneys. Erythropoietin stimulates the production of red blood cells in the bone marrow.
The average adult human produces 2 to 3 million red blood cells every second, equating to about 200 billion red blood cells every day. Some conditions, such as a low oxygen content or red blood cell count, could trigger an increased production of erythropoietin.