Hormone Levels During The Menstrual Cycle
Here's the summary ....
.... the menstrual cycle is controlled by the four female hormoes - oestrogen, progesterone, FSH and LH.
Oestrogen is responsible for building and thickening the lining of the womb [uterus] and progesterone in maintaining the lining. FSH stimulates the production of eggs and LH causes the release of the egg.
FSH and LH are controlling hormones made by the pituitary gland at the base of the brain.
And the details ....
Day 1 of the menstrual cycle is the first day of the period.
Levels of female hormones are low. So the brain begins to release FSH [follicle stimulating hormone] in order to stimulate growth of one of the eggs [follicles] in the ovary ready for the next cycle.
During the first week as a follicle grows and matures it starts to produce oestrogen, which in turn tells the brain to reduce FSH production - the follicular phase. By week two oestrogen levels are rising rapidly.
At about day 14 [in a 28 day cycle] the brain releases a short burst of LH [luteinizing hormone] which causes ovulation, or release of the egg from the follicle.
The empty follicle then collapses down, into a corpus luteum, but still has an important role in producing progesterone - the luteal phase. Progesterone is the dominant female hormone in the second half of the month. Its role is to prepare the uterus [womb] for pregnancy.
However, if the released egg is not fertilized, there is a short burst of another hormone [testosterone - not shown in the diagram] which effectively ends the sequence, causing the womb to shed its lining resulting in a menstrual period ...
... and its back to day 1.
This is a description of the regular changes that take place on a cyclical basis during menstrual periods, prior to the perimenopausal hormone fluctuations and final decline in menopause hormones.
Go to the perimenopause page to find out about hormonal changes
Or read more about hormones, their action and changes in the menopause
Return from the Menstrual Cycle to What? When? Why?
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