It is a cyclic event that takes place in human females after every 28/ 29 days. It starts from the age of puberty till the age of 50 yrs. During the process the disintegrated endometrium, blood vessels and degenerated ovum (unfertilized) is released as a menstrual flow.
It lasts upto 3-4 days. The fluid comes out through vagina. The cyclic menstruation is an indicator of normal reproductive phase/and it is in between menarche and menopause. It occurs only when the ovum is unfertilized and if fertilized then it results in pregnancy and absence of menstruation.
(b) Follicular phase:
This phase comes after menstruation. During this phase the primary follicles in the ovary grow to become a fully mature Graafian foilicle.
The endometrium of uterus regenerates through proliferation. These changes take place under the influence of pituitary and ovarian hormones. These hormones stimulate the development of follicles and attains the peak level in the middle of the cycle-the 14th day.
The rapid secretion of LH leads to maximum level during mid cycle and is called LH surge. This induces the release of ovum (ovulation). It marks the end of this follicular phase.
(c) Luteal phase:
After the follicular phase starts the luteal phase. The remaining parts of the Graafian follicle in the ovary gets transformed into corpus luteum.
It is yellow in colour. This secretes large amounts of progesterone which is needed for maintenance of the endometrium. It is requirement for implantation of the fertilized egg and then pregnancy. In case of absence of fertilization, the endometrium degenerates, egg and then pregnancy. In case of absence of fertilization, the endometrium degenerates, egg degenerates and blood vessels transforms into liquid- menstrual flow. The corpus luteum also degenerates and new menstrual cycle starts.