Biology- The Menstrual Cycle

• Menstrual cycle


  1. Days 1-9: Unfertilised egg cell is released during a period of bleeding

  2. Around day 14: Uterus lining starts to thicken again

  3. Days 15-28: Ovulation, an egg cell is released from an ovary
• Hormones involved in the menstrual cycle

  • FSH
  • LH
  • Oestrogen
  • Progesterone
• Low levels of progesterone

  Allow FSH to be produced by the pituitary gland
• FSH causes growth and maturation of the egg


  High levels of FSH stimulate the ovary to produce oestrogen
• Oestrogen causes the lining of the uterus to be built up


  High oestrogen levels cause LH to be released from the pituitary gland
• Falling concentrations of oestrogen and progesterone


  Cause the lining of the uterus to break down (menstruation)
• If an egg cell is fertilised, the corpus luteum remains large and active. A missed period is often the first sign of pregnancy because if there is no period, it means the egg cell has been fertilised
• LH causes ovulation to occur and the Corpus Luteum to be formed


  The Corpus Luteum secretes progesterone which maintains the lining of the uterus
• Fertilisation is most likely to occur during days 13-15
• Diagram of the menstrual cycle

  1. Days 1-5: Menstruation

  2. Around day 14: Uterus lining starts to thicken again

  3. Days 15-28: Ovulation, egg cell is released from the ovary