This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infeility (Eggs'plantation!), Subject name: Gynaecology & Obstetrics
[{'content': 'Mechanism of action of Clomiphene citrate used for infeility:- \nSelect and explain. \nA. Block estrogen receptors in the hypothalamus, B. Negative feedback on HPO axis, C. Direct action on ovarian primordial follicles, D. Increase in tubal motility', 'role': 'user'}, {'content': "Answer: A \nExplanation: The ability of Clomiphene citrate (CC) to initiate an ovulatory sequence is primarily due to its ability to be recognized by and interact with the estrogen receptors in hypothalamus. In its capacity as an Estrogen antagonist,CC displaces endogenous estrogen from hypothalamic estrogen receptor sites and hence inhibiting the negative feedback of the endogenous estrogen on the hypothalamus (Reproductive Medicine & Surgery, Wallach and Zacur, Mosby '95). In simple terms, there is non recognition of the body's estrogens by the hypothalamus due to the blockade of estrogens receptors by CC and hence the hypothalamus directs the pituitary to make more of FSH which in turn drives the ovary to make a follicle to make estrogens.The development of follicle is the preceeding event before ovulation.", 'role': 'assistant'}]