The menstrual cycle occurs due to changes in hormone levels in the body. Hormones are chemical messengers that interact between the brain and the ovaries, and there are four hormones involved in the control of the menstrual cycle. Of those four, two are released from the brain (Lutenising Hormone and Follicle-stimulating Hormone) and cause oestrogen and progesterone to be increased or decreased in the ovaries.
The fluctuations in oestrogen and progesterone cause the release of an egg and the lining of the uterus to build up in preparation to receive a fertilised egg. If the egg is not fertilised, levels of both hormones decrease and cause the lining of the uterus to break down causing menses (a period). This process repeats on average every 28 days (range of 21-35 days is normal) with day 1 of the cycle being the first day of bleeding.
Periods begin for girls between the ages of 8 and 15; most commonly at the age of 12.
Basic facts about the menstrual cycle:
- The menstrual cycle starts with the first day of the period (the bleed) and the cycle begins again when the next period starts.
- Hormones interact between the brain and the ovaries causing maturation of the ovaries and release of the egg.
- The menstrual cycle is much more than a period, affecting the digestive system, emotions, mental health, energy levels, and causing bloating, anxiety, cramps in the stomach and headaches, among others.