Menopause is a normal physiological process that signifies the end of the reproductive period in a woman. The process is brought about by a change in the balance of the body's sex hormones.
Hormonal changes and normal menopause
Normal women have two functioning ovaries. The ovaries have a finite number of ovarian follicles that contain the ova. At birth they contained about 700,000 sac-like follicles which each enclose an egg. Only about 400 to 500 of these follicles ever mature fully and release an egg during the menstrual cycles throughout the reproductive period of a woman’s life. The rest degenerate and disappear over the years.
During the reproductive years, the hypothalamus (in the brain) releases gonadotropin releasing hormone (GnRH). This causes the pituitary gland, located at the base of the brain, to secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH in turn stimulate the maturation of the follicles in the ovaries and the release of a new egg from its follicle each month. Every month the ovaries alternatively produce an egg (ovulation) and hormones that make the womb or uterus conducive to bearing a child.
During perimenopause the ovaries begin to shrink in size. As menopause is reached the female hormone estrogen and progesterone levels decrease. Hormone levels fluctuate during perimenopause and slowly the ovaries become resistant to FSH. This causes increased release of FSH from the pituitary to keep up estrogen production. This can cause irregular menstrual cycles and unpredictable episodes of heavy bleeding during the perimenopausal years.
Menopause causes the ovaries to stop producing an egg each month. This fall in estrogen also leads to both physical and emotional symptoms of menopause. Most women experience the menopause when they are 45-55 years of age. The average age for the menopause to occur is 52.
Causes of premature or early menopause
In some women menopause may occur before the age of 40 or 45. This is termed early or premature menopause. There are several causes of premature menopause. Some of these include:-
Premature ovarian failure
This is a rare condition. It may occur at any age and in many cases there is no cause. There is complete stoppage of functions of the ovaries and secretion of the female sex hormones. Some women with premature ovarian failure still have intermittent ovarian function - this means that their ovaries will occasionally release eggs and they may still be able to conceive.
Surgical menopause
In women who have undergone surgery for removal of the uterus (womb) and/or the ovaries due to certain pathologies before achieving menopause, there is early onset of stoppage of periods. This is also termed iatrogenic menopause as it is brought about by doctors.
Cancer chemotherapy and radiotherapy induced menopause
Radiation and chemotherapy may lead to early onset of menopause in women who have been exposed to them before achieving normal menopause.
Infections
Infections such as tuberculosis, mumps, malaria, chickenpox, shingles, dysentery due to shigella may rarely lead to early onset of menopause.
Certain diseases
Some disease and disorders may cause early onset menopause. These include hypothyroidism or underactive thyroids, Turner syndrome, Addison's disease and Down's syndrome.
Further Reading
Four genes found to significantly influence menopause timing and cancer risk