An interplay of different hormones regulates the natural cycle, ensuring regular monthly bleeding and reproductive capacity. The female sex hormones estrogen and progesterone (the hormone of the corpus luteum), which are mainly produced in the ovaries, play a major role in a woman's cycle. Certain control hormones in the brain are also involved in regulating the secretion of sex hormones.
Hormone decline at menopause
At menopause, the egg supply comes to an end and the ovaries begin to cease functioning, leading to a drop in the production of female sex hormones. At the start of the menopause, the hormonal drop mainly concerns progesterone levels, which already fall before estrogen production in turn declines, as ovulation is increasingly absent. The result is an irregular menstrual cycle.
This drop in progesterone levels, combined with high estrogen levels, leads to other noticeable changes. There may be feelings of tension in the breasts or unpleasant swelling due to water retention.
As the menopause progresses, estrogen levels also decline, leading to a number of disorders throughout the body. The most common symptoms are hot flushes and sweating, sleep disorders, depressive moods, heart palpitations and dry skin (mucous membranes). To find out more, visit our Menopause Disorders section.
The first day of monthly bleeding marks the start of a new cycle. While the uterine lining (endometrium) is still being broken down and shed, new follicles are maturing inside the ovary. The messenger substance FSH (follicle-stimulating hormone) stimulates the growth of a follicle in the ovary. As a rule, only one follicle containing an egg reaches full maturity per cycle.
Over the first 14 days of the cycle, this follicle grows to a size of around 2 centimetres. The larger the follicle, the higher the concentration of estradiol in the body.
Increased estradiol secretion signals the brain that ovulation is taking place. This in turn releases large quantities of luteinizing hormone (LH, Latin for "hormone that colors yellow") from the pituitary gland. This increase in LH concentration causes the egg to be expelled from the follicle into the Fallopian tube (ovulation). The remaining follicle then collapses on itself, developing into the corpus luteum and producing the corpus luteum hormone, progesterone.
Together, estrogen and progesterone ensure that the uterine lining is ready for implantation of a fertilized egg. The corpus luteum is preserved for around 14 days. If implantation does not take place, the corpus luteum regresses, hormone production declines and bleeding (menstruation) occurs.