Final answer:
Erythropoietin (EPO) is a hormone released by the kidneys that stimulates the bone marrow to produce red blood cells in response to low oxygen levels in the body.
Step-by-step explanation:
Erythropoietin (EPO) is a glycoprotein hormone secreted by the kidneys in response to low oxygen levels in the bloodstream. Its primary role is to stimulate the bone marrow to produce more red blood cells (erythrocytes), which carry oxygen to various tissues throughout the body. EPO is produced by interstitial fibroblast cells in the kidneys and is a crucial factor in the process of erythropoiesis, the production of red blood cells. When the blood's oxygen level is low, the kidneys release more EPO.
This increase in EPO triggers the bone marrow to accelerate the production of erythrocytes. This mechanism is especially important under circumstances such as moving to higher altitudes, where the partial pressure of oxygen is lower, or during aerobic exercise, which raises the body's oxygen requirements. Additionally, EPO production can be critical in medical scenarios, such as anemia caused by renal failure, where the body's natural EPO production is compromised, leading to diminished erythrocyte counts and reduced oxygen delivery to tissues.