What role do pituitary gonadotropins play during the follicular and ovulatory phases of the menstrual cycle? Explain the shifts in steroidal secretions.

(N/A) During the follicular phase,the secretion of gonadotropins ($LH$ and $FSH$) from the anterior pituitary increases gradually. These hormones stimulate the growth and maturation of ovarian follicles. As the follicles grow,they secrete increasing amounts of estrogens.
In the ovulatory phase,specifically around the $14^{th}$ day of the cycle,both $LH$ and $FSH$ reach a peak level,known as the $LH$ surge. This rapid surge of $LH$ induces the rupture of the Graafian follicle,leading to ovulation. Following ovulation,the ruptured follicle transforms into the corpus luteum,which secretes large amounts of progesterone,while estrogen levels remain high.