This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology and Reproduction, Subject name: Physiology
True about estrogen production in menstrual cycle. 
Select and explain. 
A. Only by theca cells, B. Only by granulosa cells, C. Both theca and granulosa cells, D. None of the above
B: Only by granulosa cells
Answer: B: Only by granulosa cells 
Explanation: Ans (b) Only by granulosa cells(Ref: Ganong, 25th ed/p.414)Estrogen is produced only by granulosa cellsThe theca interna cells supply androstenedione to the granulosa cellsGranulosa cells convert this androstenedione to estradiol with the help of an enzyme "aromatase"