Roles of Oestrogen & Progesterone in the Menstrual Cycle (Edexcel IGCSE Biology: Double Science)

• The menstrual cycle is one of the secondary sexual characteristics that starts in early adolescence in females (around age 12)
• The average menstrual cycle is 28 days long
  • Ovulation occurs around day 14, with the egg traveling to the uterus
  • If the egg is not fertilised, menstruation (period) begins due to the breakdown of the uterine lining
  • 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

Hormonal control of the menstrual cycle

• The menstrual cycle is controlled by hormones, two of which are oestrogen and progesterone
  • Oestrogen levels rise from day 1 to peak just before day 14
    • This causes the uterine wall to start thickening and the egg to mature
    • The peak in oestrogen occurs just before the egg is released
  • Progesterone stays low from day 1 – 14 and starts to rise once ovulation has occurred
    • The increasing levels cause the uterine lining to thicken further; a fall in progesterone levels causes the uterine lining to break down (menstruation / ‘period’)

Changes in the levels of oestrogen and progesterone in the blood during the menstrual cycle