What is called the menstrual cycle? Describe its phases.

(N/A) The reproductive cycle in female primates (e.g.,monkeys,apes,and human beings) is called the menstrual cycle.
The first menstruation begins at puberty and is called menarche.
In human females,menstruation is repeated at an average interval of about $28/29$ days,and the cycle of events starting from one menstruation till the next one is called the menstrual cycle.
One ovum is released (ovulation) during the middle of each menstrual cycle.
The menstrual cycle involves cyclic changes occurring in the endometrium of the uterus.
Female sex hormones,estrogen and progesterone,regulate these changes.
The events of this cycle can be divided into the following $3$ phases:
$1$. Menstrual phase (Day $1-5$): The menstrual flow results from the breakdown of the endometrial lining of the uterus and its blood vessels,which forms a liquid that comes out through the vagina. It lasts for $3-5$ days. About $50 \text{ ml}$ to $150 \text{ ml}$ of blood is lost during this time. Lack of menstruation may be indicative of pregnancy,though it may also be caused by stress or poor health.
$2$. Follicular phase (Day $6-14$): During this phase,the primary follicles in the ovary grow to become a fully mature Graafian follicle,and simultaneously,the endometrium of the uterus regenerates through proliferation. These changes are induced by pituitary and ovarian hormones. The secretion of gonadotropins ($LH$ and $FSH$) increases gradually,stimulating follicular development and the secretion of estrogens. In the middle of the cycle (about $14^{\text{th}}$ day),both $LH$ and $FSH$ attain a peak level.
$3$. Luteal phase (Day $15-28$): The remaining parts of the Graafian follicle transform into the corpus luteum,which secretes large amounts of progesterone essential for the maintenance of the endometrium.