Final answer:
FSH from the anterior pituitary gland stimulates the growth and division of follicle cells in the ovaries during the beginning of the ovarian cycle.
Step-by-step explanation:
During the beginning of the ovarian cycle, Follicle-Stimulating Hormone (FSH) from the anterior pituitary causes follicle cells to divide and grow.
Explanation: The ovarian cycle is regulated by hormones secreted by both the hypothalamus and the anterior pituitary gland. The hypothalamus produces Gonadotropin-Releasing Hormone (GnRH), which prompts the anterior pituitary to secrete FSH and Luteinizing Hormone (LH). FSH directly stimulates the follicles in the ovaries to grow, leading to the development of multiple tertiary follicles.
Although many follicles may start to grow, typically only one will fully mature and eventually release an egg during ovulation. LH also contributes to this process by inducing the production of estradiol, a form of estrogen, by the granulosa and theca cells within the follicles. This phase is known as the follicular phase and is critical for the maturation of follicles and subsequent ovulation.