This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrine Control of the Menstrual Cycle, Subject name: Gynaecology & Obstetrics
[{'content': 'Main function of B HCG: \nSelect and explain. \nA. Maintain corpus luteum, B. Stimulate decidua, C. Initiate implantation, D. initiate breast growth', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans: a (Maintain corpus luteum)Ref: William's Obstetrics, 23rd ed., Chapter 3Both alpha- and beta-chain synthesis of hCG are regulated separately. A single gene located on chromo- some 6 encodes the alpha-subunit for hCG, LH, FSH, and TSH. There are seven separate genes on chromosome 19 for the beta-hCG- beta-LH family.The best-known biological function of hCG is the so-called rescue and maintenance of function of the corpus luteum-- that is, continued progesterone production.Progesterone-producing life span of a corpus luteum of menstruation could be prolonged perhaps for 2 weeks by hCG administration.Maximum plasma hCG concentrations are attained well after hCG-stimulated corpus luteum secretion of progesterone has ceased. Specifically, progesterone luteal synthesis begins to decline at about 6 weeks despite continued and increasing hCG production.Before 5 weeks, hCG is expressed in both syncytiotrophoblast and cytotrophoblast. Later, when maternal serum levels peak, hCG is produced almost solely in syncytiotrophoblasts.", 'role': 'assistant'}]