This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'In a person acclimatized for high altitude, O2 saturation is maintained because of \nSelect and explain. \nA. Increase Hb concentration, B. Increase blood volume, C. Better duffusion in lungs, D. All of the above', 'role': 'user'}, {'content': 'Answer: D \nExplanation: In acclimatization erythropoietin secretion increases promptly on ascent to high altitude and then falls somewhat over the following 4 d as the ventilatory response increases and the aerial PO2 rises. The increase in circulating red blood cells triggered by the erythropoietin begins in 2 to 3 d and is sustained as long as the individual remains at high altitude. Compensatory changes also occur in the tissues. The mitochondria, which are the site of oxidative reactions, increase in number, and myoglobin increases, which facilitates the movement of O2 into the tissues. The tissue content of cytochrome oxidase also increases.Ref: Ganong review of medical physiology 23rd edition Page no: 619', 'role': 'assistant'}]