This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood Physiology, Subject name: Physiology
[{'content': 'Erythropoietin is secreted by: \nSelect and explain. \nA. Coical interstitial cells, B. Cells in macula densa, C. Granular cells, D. Mesangial cells', 'role': 'user'}, {'content': 'Answer: A \nExplanation: JG apparatus Cells in macula densa Granular cells/ JG cells Mesangial cells Senses Na+ & Cl- in tubular fluids & initiate tubuloglomerular feedback. Synthesis & secrete renin Cells that can alternate the vessel diameter. Type I Coical interstitial cells : synthesize erythropoietin', 'role': 'assistant'}]