Sexual Hormones in Humans (Cambridge (CIE) IGCSE Combined Science): Revision Note

The Menstrual Cycle

• Starts in early adolescence in girls (around age 12) and is controlled by hormones

• The average menstrual cycle is 28 days long

• Ovulation (the release of an egg) occurs about halfway through the cycle (day 14) and the egg then travels down the oviduct to the uterus

• Failure to fertilise the egg causes menstruation (commonly called a period) to occur - this is caused by the breakdown of the thickened lining of the uterus

• Menstruation lasts around 5 - 7 days and signals the beginning of the next cycle

  After menstruation finishes, the lining of the uterus starts to thicken again in preparation for possible implantation in the next cycle

Changes in the lining of the uterus during the menstrual cycle