The synthesis of hormones
Menopause depends on a complex network of hormonal communications between the ovary, hypothalamus, and pituitary gland in the brain. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) which triggers the production of follicle-stimulating hormone (FSH) by the pituitary gland. The FSH then stimulates the growth of the egg follicles in the ovaries to trigger ovulation. As the egg follicles grow, oestrogen is manufactured and released into the blood.
This chain reaction is not just one-way. Oestradiol, one of the ovarian oestrogens in the bloodstream, also acts on the hypothalamus, causing a change in GnRH. Next, this altered hormone stimulates the pituitary gland to produce luteinising hormone (LH) which causes the egg follicles to burst and the ovum to be released. After the egg is expelled, progesterone is also manufactured by the collapsed egg follicle which develops into the corpus luteum.
For the first eight days of the menstrual cycle, a woman's ovaries make lots of oestrogen. Oestrogen prepares the follicles for the release of one of the eggs. The rate of oestrogen secretion begins to fall around day 13 or one day before ovulation occurs. As oestrogen falls progesterone begins to rise, stimulating very rapid growth of the follicle.
Beginning with this secretion of progesterone, ovulation also occurs. After the egg has been released from the follicle (known as the luteal stage of a woman’s cycle), the follicle enlarges and becomes the corpus luteum. Progesterone is secreted from the corpus luteum, a temporary endocrine structure with a huge capacity for hormone production. The surge of progesterone at the time of ovulation is the source of libido.
Hormones are secreted not in a constant, steady manner but at dramatically different rates during various phases of the 28-day menstrual cycle.
After 10 to 12 days, ovarian production of progesterone falls dramatically if fertilisation does not take place. It is this sudden decline in progesterone levels that triggers the shedding of the secretory endometrium (the menses), leading to a renewal of the entire menstrual cycle.
Ovarian oestrogen and progesterone stimulate the growth of the endometrium (lining of the uterus) in preparation for fertilisation. Oestrogen proliferates the growth of endometrial tissue, while progesterone facilitates the secretory lining of the uterus so the fertilised egg can implant successfully. Adequate progesterone, therefore, is the hormone most essential to the survival of the fertilised egg and foetus.
Midlife & your hormones
The interaction between hormones begins to alter when a woman approaches 40. These alterations will eventually lead to menopause around the age of 50. Changes commonly start in the hypothalamus and the pituitary gland rather than in the ovaries. Whatever the mechanism triggering menopause, fewer egg follicles are stimulated so the amount of oestrogen and progesterone being produced by the ovaries declines. With the reduction of these hormones, menstruation becomes scantier and erratic and eventually ceases.
However, other parts of the body such as the adrenal glands, skin, muscle, brain, pineal gland, hair follicles and body fat also produce these same hormones, enabling the body to make healthy adjustments in hormonal balance after menopause. Of course, this depends on how a woman has taken good care of herself during the premenopausal years in terms of diet and lifestyle as well as mental and emotional health.
With age, the ovaries become less responsive to pituitary gonadotrophins. This results in:
- shorter follicular phases (thus shorter menstrual cycles)
- fewer ovulations
- decreased progesterone production
- irregularity in cycles
- increased levels of LH and FSH
When the follicles fail to respond, oestrogen is no longer produced and circulating levels of FH and FSH rise substantially. Other hormonal changes which take place are:
- Androstenedione is reduced by half.
- Testosterone decreases only slightly – from the stroma of the postmenopausal ovary and the adrenal glands.
- Androgens are converted to oestrogens in the periphery (fat cells, skin, liver), accounting for most of the circulating oestrogen in postmenopausal women.
The perimenopausal phase starts slowly and most women are unaware that the physiology of their body is changing. Often these changes take place two to three years prior to any noticeable physical changes in the monthly cycle. The output of both oestrogen and progesterone declines gradually and may take place alongside the gradual variations in the pattern of a woman's cycle.
Supporting these changes creates a harmonious transition towards menopause. This is why it is so important for women to understand their bodies. This may be one of the reasons why some women who naturally ease into menopause without the need for medication experience fewer aggravating symptoms. In contrast, women who are forced into a menopausal state via drugs or surgery experience more full-blown symptoms.
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