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 is secreted from: 
Select and explain. 
A. Juxtaglomerular cells, B. Macula densa, C. Interstitial cells, D. Glomerulus
C: Interstitial cells
Answer: C: Interstitial cells 
Explanation: In adults, about  85% of the erythropoietin comes from the kidneys and 15% from the liver. 
Erythropoietin is produced by interstitial cells in the peritubular capillary bed of the kidneys and by perivenous hepatocytes in the liver.