Final answer:
Ovulation occurs at the end of the proliferative phase, just before the onset of the secretory phase of the menstrual cycle.
Step-by-step explanation:
Ovulation takes place at the end of the proliferative phase of the menstrual cycle. During the proliferative phase, which ranges from day 7 to 14, estrogen secreted by cells of the maturing ovarian follicle causes the lining of the uterus to grow. This sets the stage for ovulation, which is the release of an egg from the ovary. Once ovulation occurs, the ovarian cycle enters its luteal phase, and the menstrual cycle enters its secretory phase.
The secretory phase is marked by the production of progesterone by the corpus luteum in the ovary. This hormone stimulates changes in the endometrium to make it more receptive to implantation of a blastocyst, should fertilization occur. It lasts for the second half of the uterine cycle, approximately from day 15 to 28. Therefore, ovulation occurs before the secretory phase and marks the transition from the proliferative phase to the secretory phase of the menstrual cycle.