When arterial oxygen levels are low, what hormone do the kidneys increase production of to stimulate red blood cell production?

When arterial oxygen levels are low, the kidneys respond by increasing the production of erythropoietin. This hormone plays a crucial role in the regulation of red blood cell production in the bone marrow. Erythropoietin is secreted in response to hypoxia, or reduced oxygen levels in the blood, as the body attempts to boost the oxygen-carrying capacity by producing more red blood cells.

The increase in erythropoietin stimulates the erythropoiesis process, leading to an increase in the number of red blood cells, which in turn enhances oxygen delivery to tissues. This response helps maintain adequate oxygen levels in the body, counteracting the effects of hypoxia.

Other options such as oxygen, hemoglobin, and iron, while related to the overall process of oxygen transport and utilization, do not directly stimulate red blood cell production in the way that erythropoietin does. Thus, the correct answer reflects the specific hormonal response of the kidneys to low oxygen levels, emphasizing the importance of erythropoietin in hematopoiesis (the formation of blood cellular components).