Natural menopause, also known as spontaneous menopause, is defined as permanent cessation of menstrual periods due to loss of ovarian follicular function. This means that the ovarian follicle, whose role is to secrete female sex hormones and release ripened eggs, ceases to operate.
Menopause that has been induced through medical intervention such as ovarian removal, or ovarian damage due to surgery, chemotherapy, or pelvic radiation therapy is known as surgical menopause.
In the case of a hysterectomy, removal of ovaries will result in an immediate menopause. When the ovaries are not removed during the procedure, there is a 50% chance of experiencing menopause within the 5 years following surgery.
The average age for experiencing natural menopause is 51.4 years. For most women it occurs around 45-55 years, though it can occur as early as 30 or as late as 60.
The exact events that cause the onset of perimenopause, and eventually the menopause itself, are not yet known, but there are three major physical changes that occur.
In order to understand the significance of these events, it is necessary to start from the beginning of the story.
Reproductive life / menstrual cycles
Female humans possess their greatest number of eggs, between 6 and 7 million, when they are five-month-old foetuses. From this moment on the eggs begin to die. Until puberty occurs, the eggs are in an immature state. Shortly after a girl's first period, these eggs begin to mature, and continue to do so until about 2 years before the menopause.
Approximately once a month a mature egg is released from one of the ovaries. In preparation for the possibility that this egg may be fertilised, the lining of the womb begins to thicken in order to house and protect the resulting embryo. If the egg is not fertilised during that cycle, this excess lining is shed. This is the event known as a period.
The maturation and release of eggs, and thickening and shedding of womb lining are all mediated by a cascade of hormonal events.
The hypothalamus is an endocrine gland situated in the brain. Hypothalamic hormones control another gland, found at the base of the brain, known as the pituitary. Hormones released from here in turn control the release of female sex hormones, oestrogen and progesterone, from the ovaries.
Together these hormones govern the reproductive system by affecting the breasts, vagina, ovaries, cervix (neck of the womb), and the womb - or endometrium - itself.
At puberty, it takes time for the cycle of hormonal events to settle, resulting in irregular periods of varying intensity, and inevitable hormonally charged mood swings.
Throughout reproductive life, the chain of hormonal events settles into a routine.
What happens at menopause / perimenopause?
During the menstrual transition, the chain begins to falter. Disruptions similar to those experienced at puberty occur as hormones begin to wind down.
Their production and release becomes erratic, and decreased levels followed by sudden surges lead to irregular periods, erratic circulatory responses (often resulting in the characteristic 'hot flush'), and mood swings.
Oestrogen and progesterone, although still produced in small amounts, eventually cease to achieve levels sufficient to trigger the events described above. When this stage is reached, the ovaries stop releasing eggs, and the menstrual periods cease.
The medical profession defines the menopause as 'cessation of periods', its literal translation. It is often heard of women 'going through' the menopause, but it is more accurate to say that a woman 'reaches' it.
The menopause is one point in time, which occurs with the final menstrual period. The time surrounding this point plus the changes that happen to a woman approaching it and the year following the menopause are called the 'perimenopause'.
More specifically, the time prior to the final period, when variability within the cycle is at its greatest, is known as the menstrual transition. The normal reproductive life of a woman before she reaches this stage is known as 'premenopause', and the years following the menopause, after the initial year, which is encompassed by the term perimenopause, are known as postmenopause.
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