Four Hormones in the Menstrual Cycle (OCR Gateway GCSE Biology: Combined Science)

Higher Tier Only
Introduction to the menstrual cycle

• The average menstrual cycle is 28 days long and there are four main stages:
1. Menstruation lasts around 5 - 7 days and signals the beginning of the cycle
2. Thickening of the uterus lining occurs after menstruation finishes, in preparation for possible implantation in the next cycle
3. Ovulation (the release of an egg) occurs on around day 14, about halfway through the cycle and the egg then travels down the oviduct to the uterus
4. Maintenance of the uterus lining ready to accept a fertilised egg

Hormones of the menstrual cycle

• Four hormones control the events that occur during the menstrual cycle
  • Follicle-stimulating hormone (FSH) is produced by the pituitary gland in the brain and causes maturation of an egg in the ovary
  • Luteinising hormone (LH) is produced by the pituitary gland in the brain and stimulates ovulation (the release of the egg)
  • Oestrogen is produced by the ovaries and is involved in building up the lining of the uterus
  • Progesterone is produced specifically by an empty egg follicle called the corpus luteum and is required to maintain the lining of the uterus

The stages of the menstrual cycle

• The cycle begins after menstruation when the pituitary gland produces FSH which stimulates the development of a new follicle in the ovary
• An egg matures inside the follicle and the follicle produces the hormone oestrogen –
  • So it can be said that FSH stimulates the production of oestrogen
• Oestrogen causes growth and repair of the lining of the uterus wall and inhibits the production of FSH
• When oestrogen rises to a high enough level it stimulates the release of LH from the pituitary gland which causes ovulation (usually around day 14 of the cycle)
• The follicle becomes a corpus luteum and starts producing progesterone
• Progesterone maintains the uterus lining (the thickness of the uterus wall)
• If the egg is not fertilised...
  • The corpus luteum breaks down and progesterone levels drop
  • This causes menstruation – commonly known as having a period
• If fertilisation does occur...
  • The corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down (breakdown of the lining would prevent a pregnancy)
  • Once the placenta has developed, it starts secreting progesterone and continues to do so throughout the pregnancy to maintain the lining

Changes in the levels of the pituitary hormones FSH and LH in the blood during the menstrual cycle

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