-THE BIOLOGY OF PUBERTY AND MENOPAUSE
Although in most societies, the female menses is regarded as one of the most cardinal feature of woman hood and an indication of a woman’s potential fertility, many biological changes occur within the woman’s body starting right from child hood, progressing into adult hood and eventually ending in menopause. These biological changes are the main determinant of the reproductive capability of a woman and menstruation is only one of the many outward manifestations of this natural process. In this section, we are going to look at the natural process that transforms a young girl from a child into an adolescent and then eventually results in menopause along with the reproductive implications of this process. But before we go on, kindly look at the meaning of the basic terms that will be used in this article and in many to follow in MENSTRUATION AND MENSTRUAL CYCLE: INTRODUCTION.
THE BIOLOGY OF PUBERTY AND MENOPAUSE
During childhood, the hypothalamic– pituitary–ovarian (HPO) axis in young girls is suppressed and the levels of the hormones, GnRH, FSH and LH are very low; but as a girl matures, changes occur within her body that result in an increase in the level of these hormones eventually kick starting the process of puberty. Although, the exact mechanism determining the onset of puberty is unknown, various factors that may influence the onset of puberty include race, heredity, body weight and exercise. In general, the black race and a fat stature are associated with an earlier onset of puberty than the white race, a lean stature and a lifestyle of active exercise which are associated with a later onset of puberty. At the onset of puberty (8 to 12 years with an average of 10 years), the hormone GnRH is secreted in pulses, initially at night but gradually extending towards the day as puberty progresses. This in turn stimulates the secretion of FSH and LH by the pituitary glands, both in turn triggering the growth of the ovarian follicles and the secretion of the ovarian sex hormones. The physical changes seen in puberty are initiated by oestrogen, which is the most predominant sex hormone produced by the ovaries. The physical changes occurring in puberty, are breast development, growth of the pubic hair, growth of the axillary hair or armpit, a rapid increase in height and the onset of menstruation. The first menses a young girl experiences at puberty is known as menarche. Although the average age of menarche is about 12 to 13 years, it may take about three years before the menstrual cycle establishes a regular pattern. This is because the HPO axis is initially immature and the GnRH secretions are initially sub-optimal, hence, the initial cycles are often anovulatory, unpredictable and irregular. But once the GnRH secretion becomes optimal, the menstrual cycle becomes ovulatory and regular, while the HPO axis is then regarded as matured.
The female reproductive potential is directly proportional to the number of oocytes present within the ovaries. The number of oocytes is highest when the female unborn child is still within her mother’s womb. These oocytes gradually decreases in number, such that from about a million to two million oocytes present in the ovary at birth, only about 400,000 is left in the ovary at puberty. This is a natural phenomenum that ensure that only the best oocytes are retained for future reproduction. The rate of loss of these oocytes however accelerates after the age of 37 in an average healthy woman, or at an earlier age in women who have had long term GnRH deficit, or a previous exposure to toxic substances that can damage the oocytes, such as chemotherapy, radiotherapy and infection of the ovaries, until a point is reached when a total depletion of the oocytes occur in the ovary. This period which is associated with a decrease in the reproductive potential and fertility rate, is initially associated with irregular menses due to anovulatory cycles and a decrease in the amount of the female sex hormones secreted by the ovaries creating changes in the body known as perimenopausal symptoms. The last menstrual period experienced afterward is referred to as the menopause and signifies an end to the reproductive career of a woman. For more information, please CHAT WITH OUR CONSULTANTS.