This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology in Relation to Reproduction, Subject name: Gynaecology & Obstetrics
[{'content': 'Corpus luteum formation occurs on _______ of menstrual cycle: \nSelect and explain. \nA. 15th day, B. 22nd day, C. 1st day, D. 28th day', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) 15th dayRef.: D.C. Dutta 8th ed. / 22; Williams Obstetrics 23rd ed. Ch: 3* Following ovulation (14th day) the remaining follicular cells left by the ovulated follicle differentiate into the corpus luteum (meaning yellow body.).* Corpus luteum secrets progesterone, which causes secretory changes in endometrium.MENSTRUAL PHASESCycle Day1-56-1415-28Ovarian phaseEarly follicleFollicularLutealEndometrial phaseMenstrualProliferativeSecretoryEstrogen/ ProgesteroneLow levelsEstrogenProgesterone', 'role': 'assistant'}]