From the Guidelines
The correct answer is d. Hypoxic stimulus, such as ascending to a high altitude. Erythropoietin (EPO) is a hormone primarily produced by the peritubular fibroblasts in the kidney cortex in response to decreased oxygen levels in the blood. When a person ascends to high altitude, the partial pressure of oxygen decreases, leading to tissue hypoxia. This hypoxic state triggers the production of hypoxia-inducible factor (HIF), which then stimulates EPO production 1. The increased EPO stimulates the bone marrow to produce more red blood cells, thereby increasing oxygen-carrying capacity as an adaptive response to the hypoxic environment. This physiological response helps the body compensate for the reduced oxygen availability at high altitudes. In contrast, polycythemia vera involves increased red cell production independent of EPO levels, leukocytosis affects white blood cells, dehydration doesn't directly stimulate EPO, and hemolysis products don't increase EPO production. Some conditions, such as malignant or benign tumor tissue, can lead to hypoxia-independent EPO production, but these are distinct from the physiological response to hypoxia 1. Key points to consider include:
- Hypoxic stimuli, like high altitude, increase EPO production
- Polycythemia vera is characterized by increased red cell production independent of EPO levels
- Leukocytosis, dehydration, and hemolysis products do not directly stimulate EPO production
- Hypoxia-independent EPO production can occur in certain conditions, but is not relevant to the physiological response to hypoxia.