Final answer:
The ovary begins secreting oestrogen during the follicular phase of the menstrual cycle as the follicles on the ovary surface grow and prepare for ovulation. Oestrogen levels rise and contribute to the regulation of other hormones like FSH and LH, leading to ovulation around day 14. After ovulation, the corpus luteum maintains oestrogen and progesterone levels to prepare the endometrium for implantation.
Step-by-step explanation:
The ovary starts secreting oestrogen during the first half of the ovarian cycle, known as the follicular phase. This phase is characterized by the growth of follicles on the surface of the ovary, which prepare the egg for ovulation. The secretion of oestrogen begins as these follicles develop, and the hormone plays a crucial role in regulating the menstrual cycle and preparing the female body for possible pregnancy. Specifically, the growing follicle releases increasing amounts of oestrogen, which eventually leads to a decrease in follicle-stimulating hormone (FSH) due to negative feedback and the atresia of all but one of the developing tertiary follicles. This elevated production of oestrogen from the dominant follicle then switches to positive feedback, which stimulates the luteinizing hormone (LH) surge and triggers ovulation, typically around day 14 of a 28-day menstrual cycle.
Following ovulation, the luteinization of granulosa cells of the collapsed follicle forms the progesterone-producing corpus luteum, marking the beginning of the luteal phase. The corpus luteum produces both progesterone and also oestrogen, stabilizing and preparing the endometrial lining for potential implantation of a fertilized egg.