3.10B Roles of FSH & LH in the menstrual cycle (Edexcel IGCSE Biology)

The roles of FSH and LH

• FSH (follicle-stimulating hormone) is released by the pituitary gland and causes an egg to start maturing in the ovary
• It also stimulates the ovaries to start releasing oestrogen
• The pituitary gland is stimulated to release luteinising hormone (LH) 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

• The pituitary gland produces FSH which stimulates the development of a follicle in the ovary
• An egg develops inside the follicle and the follicle produces the hormone oestrogen
• Oestrogen causes growth and repair of the lining of the uterus wall and inhibits 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 the corpus luteum and starts producing progesterone
• Progesterone maintains the uterus lining (the thickness of the uterus wall)
• If the ovum is not fertilised, the corpus luteum breaks down and progesterone levels drop
• This causes menstruation, where the uterus lining breaks down and is removed through the vagina - commonly known as having a period
• If pregnancy does occur the corpus luteum continues to produce progesterone, preventing the uterus lining from breaking down and aborting the pregnancy
• It does this until the placenta has developed, at which point it starts secreting progesterone and continues to do so throughout the pregnancy

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