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B1 Hormones and the Menstrual Cycle
Below is a summary of everything you need to know about the Menstrual Cycle for AQA Biology 1
The monthly release of an egg and the build up and break down of the lining of the uterus is called
the menstrual cycle.
The Menstrual cycle consists of four main stages:
Stage 1 The bleeding starts. The lining of the uterus continues breaking down for about four days
Stage 2 The lining of the uterus starts building up for about 4-14 days. This creates a thick spongy
layer full of blood vessels
Stage 3 A matured egg is released from one of the ovaries on day 14
Stage 4 The lining of the uterus is maintained from day 14-28. If a fertilised egg has not landed on
the wall of the uterus by day 28, the lining breaks down and the cycle starts again
Hormones are chemical messengers which travel in the blood to activate target cells. They play a
main role in the menstrual cycle. The main three hormones are FSH, LH and oestrogen.
FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are both produced and secreted by
the pituitary gland. Oestrogen is produced and secreted by the ovaries.
FSH Causes an egg to mature in one of the ovaries and stimulates the release of oestrogen
Oestrogen Thickens the lining of the uterus, inhibits the further release of FSH and stimulates the
release of LH
LH Causes a matured egg to be released from the ovaries
This diagram is showing what happens visually on each of the days. As you can see, on day 1,
menstruation is happening, where the lining of the uterus is breaking down. Then the lining builds
up. The lining is then maintained, but eventually breaks down if a fertilised egg is not received.