This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematopoeisis: Basic concepts, Subject name: Pathology
Erythropoetin in fetus is secreted by? 
Select and explain. 
A. Liver, B. Marrow, C. Spleen, D. Kidney
A: Liver
Answer: A: Liver 
Explanation: Sources of erythropoietin: Fetus: Liver Adult: Interstitial cells in peritubular capillary bed of kidneys (85%). Perivenous hepatocytes in the liver (15%). Brain (protective effect against excitotoxic damage triggered by hypoxia).