WHY DO THE CLIMATERIC AND MENOPAUSE OCCUR?

To understand this better, read Physiology of menstruation
The production of Oestradiol (a hormone) is a by-product of maturation of the egg. Progesterone (another hormone) is produced by the ovary only after ovulation . With increasing age, ovaries do not respond to stimulation as before.

This together with depletion and finally exhaustion of eggs, results in a gradual decline in oestradiol production. When eggs don't get produced, there is a loss of progesterone production by the ovary. Eventually, oestradiol production falls below a critical threshold and endometrial stimulation no longer occurs and a woman stops getting periods.