It involves a number of cyclic changes occurring in ovary and the uterus. It begins in females at puberty at the age of 11-13 years and continues till the age of 50-55 years.
Various phases of the menstrual cycle
Menstrual phase: It involves the breakdown of lining of uterus. The lining along with blood vessels gets slashed off and is discharged from vagina. Uterine bleeding called menstruation usually lasts for 4-6 days.
Proliferative phase: It involves the repair and thickening of lining of uterus. During this stage only one ovum out of thousands matures from one of the two ovaries and enlarges. This stage lasts from 5' day to 14th day i.e. till ovulation.
Ovulation phase: On the 14th day, a mature ovum is released from the ovary. The ovum is immediately picked up by the funnel shaped opening of the fallopian tubes.
Secretory phase: It lasts from the 14" day to 28' day. It involves the changes occurring in endometrium characterized by secretory activity of uterine glands.