<prompt> Corpus luteum formation occurs on ___ of menstrual cycle:15th day22nd day1st day28th day  <response>: 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 