Roles of Oestrogen & Progesterone in the Menstrual Cycle (Edexcel IGCSE Biology (Modular): Unit 2): Revision Note

The Menstrual Cycle

• The menstrual cycle begins after puberty, usually in early adolescence (around age 11–14)

• The average menstrual cycle lasts about 28 days, though it can vary between individuals

  • Ovulation occurs around day 14, when an egg is released from an ovary and travels along the fallopian tube towards the uterus

  • If the egg is not fertilised, the uterine lining (endometrium) breaks down and is shed through the vagina — this is called menstruation (a period)

  • Menstruation usually lasts around 5 - 7 days and marks the start of the next cycle

  • After menstruation, the uterine lining thickens again in response to hormones, preparing for the possible implantation of a fertilised egg

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