Final answer:
Erythropoietin (EPO) is a hormone secreted by the kidneys that stimulates the production of red blood cells in response to low oxygen levels in the blood.
Step-by-step explanation:
The hormone that stimulates the production of red blood cells (RBCs) is known as erythropoietin (EPO). This glycoprotein hormone is secreted by the interstitial fibroblast cells of the kidneys when there is a decrease in oxygen levels in the blood. EPO triggers the bone marrow to produce more erythrocytes (RBCs), thus raising the oxygen-carrying capacity of the blood. Athletes have been known to misuse synthetic forms of EPO for performance enhancement, also known as blood doping, although EPO is banned in most organized sports. However, it is also used medically to treat certain types of anemia and other disorders where an increase in erythrocytes and oxygen levels is beneficial.