Which hormone released from the kidneys promotes the production of red blood cells (RBC)?

The hormone that promotes the production of red blood cells (RBCs) and is released from the kidneys is erythropoietin. This hormone is crucial in the process of erythropoiesis, which is the formation of red blood cells in the bone marrow. When the kidneys detect low levels of oxygen in the blood, typically due to decreased RBC count or low hemoglobin levels, they secrete erythropoietin. This hormone then stimulates the bone marrow to produce more red blood cells, increasing the oxygen-carrying capacity of the blood.

Erythropoietin is a vital component of the body's response to hypoxia, or low oxygen levels, ensuring that tissues receive adequate oxygen for proper function. Its regulation is part of a feedback mechanism that balances RBC production with the body’s oxygen needs.

The other hormones listed—testosterone, insulin, and cortisol—do not have a direct role in stimulating the production of red blood cells from the kidneys. Testosterone can indirectly influence erythropoiesis by stimulating erythropoietin production, but it is not the primary hormone responsible for RBC production. Insulin is primarily involved in carbohydrate metabolism and does not affect red blood cell production. Cortisol, while it has