6.4 The menstrual cycle
What is menstruation, and how does it occur?
For females, the first sign of puberty is usually the release of blood and tissue from the body through the vagina. This is called menstruation.
Every month, a cycle of events takes place in the female reproductive system to bring about menstruation. This monthly event is known as the menstrual cycle. The duration and amount of blood produced differ from individual to individual.
A menstrual cycle usually lasts about 28 days--the length of time from the first day of one menstrual period to the day before the next one begins.
The menstrual cycle prepares the uterus to receive the fertilised egg. Menstruation occurs if the egg released by the ovary is not fertilised.