Roles of FSH & LH in the menstrual cycle (Edexcel IGCSE Biology)

• In addition to oestrogen and progesterone, the menstrual cycle is controlled by FSH and LH
• Both of these hormones are released from the pituitary gland in the brain
  • FSH (follicle-stimulating hormone) causes an egg to start maturing in the ovary
    • It also stimulates the ovaries to start releasing oestrogen
  • LH (luteinising hormone) is released when oestrogen levels have reached their peak
    • LH causes ovulation to occur and also stimulates the ovary to produce progesterone

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

Interaction between all four of the menstrual cycle hormones

1. The pituitary gland releases FSH to develop an ovarian follicle
2. The follicle produces an egg and oestrogen
3. Oestrogen stimulates uterine lining growth and inhibits FSH production
4. High oestrogen levels trigger LH release from the pituitary, causing ovulation (around day 14)
5. The follicle becomes the corpus luteum, producing progesterone
6. Progesterone maintains the uterine lining
7. If the egg isn't fertilised, the corpus luteum breaks down, progesterone levels drop, and menstruation occurs
8. If pregnant, the corpus luteum continues producing progesterone until the placenta develops, which then maintains progesterone production throughout pregnancy

Diagram showing where hormones involved in the menstrual cycle are made and act