This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Erythropoietin secretion occurs when: 
Select and explain. 
A. Tissue pO2 concentration, B. T Tissue pH, C. T Tissue pCO2 concentration, D. T Hemoglobin
A: Tissue pO2 concentration
Answer: A: Tissue pO2 concentration 
Explanation: A i.e. 4, Tissue PO2 concentrationThe only physiological stimulus for erythropoietin secretion is Hypoxia or decreased paial pressure of oxygenQ.