(A) The menstrual cycle consists of four main phases: menstruation,follicular phase,ovulatory phase,and luteal phase.
During the follicular phase,primary follicles in the ovary grow and develop into a fully mature Graafian follicle.
Simultaneously,the endometrium of the uterus undergoes regeneration through the process of proliferation.
These changes are regulated by the levels of pituitary hormones ($LH$ and $FSH$) and ovarian hormones (estrogens).
$LH$ and $FSH$ levels increase during this phase,stimulating follicular development and the secretion of estrogens by the growing follicles.
Both $LH$ and $FSH$ reach their peak levels in the middle of the cycle (around the $14$th day). The rapid surge of $LH$,known as the $LH$ surge,induces the rupture of the Graafian follicle,leading to the release of the ovum,which is known as ovulation.