The Menstrual Cycle and Hormone Interaction

This lesson provides a deeper examination of the interactions between the four key hormones of the menstrual cycle, as required by the AQA GCSE Combined Science Trilogy specification (8464). Understanding these interactions — including feedback loops — is essential for achieving the highest grades.

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Recap: The Four Hormones

Hormone	Source	Primary Role
FSH	Pituitary gland	Stimulates egg maturation in the ovary; stimulates oestrogen production
Oestrogen	Ovaries	Thickens the uterus lining; inhibits FSH; stimulates LH release
LH	Pituitary gland	Triggers ovulation (~day 14)
Progesterone	Ovaries (corpus luteum)	Maintains the uterus lining; inhibits FSH and LH

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Detailed Hormone Interactions Throughout the Cycle

Days 1–5: Menstruation

• Progesterone levels have dropped (the corpus luteum has broken down).
• Without progesterone, the uterus lining cannot be maintained, so it breaks down and is shed (menstruation / period).
• Low levels of progesterone and oestrogen mean the pituitary gland is no longer inhibited.
• The pituitary gland begins to release FSH again.

Days 6–13: Follicular Phase