KNOWING YOUR BODY AND HOW IT WORKS

For a good understanding of menopause, it is important to know something of the workings of the human female body.

Essential female organs

 Anatomically the female internal genitalia lie in the pelvic cavity on the pelvic floor. The pelvic floor is the lower part of the female body surrounded by two bones, one on either side, called the pelvic bones. These bones are covered by muscles, fascia and skin, like a thick curtain separating the inside organs from the outside world. These tissues make up the pelvic floor.

 In front of the uterus lies the urinary bladder. The bladder tube, called the urethra, opens in front of the vagina. Behind the uterus lies the last part of the bowel called the rectum. Its outside opening, the anus, lies behind the vaginal opening. The uterus is kept in place by many sheet like tissues called ligaments which are attached to the pelvic bones like ropes securing a tent to its pegs. Childbirth weakens the pelvic floor and contributes to prolapse (falling down) of the pelvic organs: the bladder, uterus and rectum. 

The ovaries and the Fallopian tubes

 The ovaries are greyish yellow in colour and solid, generally the size of a hazelnut but with variation depending on their dynamic state. 

 Externally, the genital organs are the opening of the vagina and the surrounding folds of skin. The vagina is protected by a perforated membrane called the hymen. The vaginal opening is surrounded by two little folds of skin called the labia minora. Where these folds join is a small cylindrical projection called the clitoris. Richly supplied with blood vessels and nerves, the clitoris is subject to arousal. The labia minora are surrounded by two further folds of skin on either side called the labia majora. Like the labia minora, they become thin (atrophic) with age because of the declining oestrogen supply.

The Bartholins glands, one on each side of the opening of the vagina, secrete fluids during sexual activity which further helps to lubricate the vaginal area.

Endocrine glands and hormones

Most bodily functions are controlled by natural chemicals — hundreds of them. One group of chemicals, called hormones, is secreted by specialised glands, the endocrines. These hormones are carried to distant organs via the blood stream where they exert their effect. They influence activities such as the regulation of body temperature, metabolism, repair, growth and reproduction. A proper balance of hormones is important in maintaining our mental and physical wellbeing. Significant or prolonged disturbances in this finely-tuned hormone balance may result in endocrine disorders such as diabetes or goiter. Many medical experts feel that menopause is also an endocrine disorder since the oestrogen deficiency that occurs after menopause differs so markedly from the premenopausal state. Others argue that the loss of oestrogen production after menopause is a natural part of the ageing process.

            In the human body there are seven main endocrine glands and many hormones. Located deep in the brain is the region called the hypothalamus which influences functions such as body temperature control, the wake- and—sleep cycle, blood pressure, water balance, sweat secretion and sexual behavior. It also produces hormones which control the activity of another endocrine gland called the pituitary gland situated nearby. The pituitary in turn influences the activities of other endocrine glands including the thyroid, adrenals and the ovaries. For this reason the pituitary is often called the master gland.

            The thyroid gland is located in the neck. It is responsible for maintaining many aspects of the body’s metabolism or chemistry; it is the energy control mechanism. This gland can become over- or under- active causing women to be over—active or slow and tired. These disorders often occur at the time of menopause.

            Embedded in the thyroid gland are four parathyroid glands which help to maintain proper blood levels of calcium, and therefore play a role in the maintenance of bone calcium and bone density. The cells responsible for secretion of insulin which controls blood sugar levels are located in the pancreas and are called the Islets of Langerhans.

Lack of insulin causes diabetes. Menopause is sometimes said to be analogous to diabetes, since the lack of oestrogen and lack of insulin both adversely affect, many parts of our body.

            There are two adrenal glands, one located on the top of each kidney. They secrete several hormones which influence salt and fluid balance, blood pressure, skin pigmentation and the body’s response to stress. Small amounts of male sex hormones, androgens, are also produced in the adrenals of men and women. These can be converted to oestrogens in the body fat of women, and represent the main source of oestrogens in women after menopause.The main hormones involved in menopause are called sex hormones, and are secreted by specialised endocrines called sex glands: ovaries in women and testes in men.

The ovaries

            Women have two ovaries. If one is not working, the other can carry out the complete function of both. This amazing organ lies dormant until puberty at which time it becomes constantly active creating regular monthly cycles extending over thirty to forty years. This activity finally comes to an end at menopause.

            The ovaries’ function is to facilitate and maintain pregnancy, and they do so by secreting oestrogens and progesterone. This function is realised through the complex menstrual cycle which is also influenced by hormones from the hypothalamus and the pituitary gland. Ovaries also secrete small amounts of the male hormones, androgens.

Each ovary consists of two layers, the outer cortex and the inner medulla. The outer-most layer of the cortex forms a covering which has a supporting mesh called the stroma. In the stroma, along with blood vessels and nerves, are scattered immature eggs called primordial follicles. In the developing foetus, the first sign of ovarian formation appears around six to eight weeks after conception. At this time, millions of primordial follicles are stored in the fetal ovary. By twenty weeks of foetal life there are seven to ten million primordial follicles which are rapidly reduced to two million at birth and then slowly reduced to three to four hundred thousand at puberty. Some forty years later only a few hundred follicles are left, and these are incapable of maturation or hormone secretion.

Menopause means no more egg maturation and therefore very little oestrogen

Age

20 weeks of foetal life                     20million primordial follicles (egg buds)

At birth                                            2 million primordial follicles

At puberty                                        500 thousand primordial follicles

Menopause                                       Few or no primordial follicles

            Despite decades of medical research some aspects of ovarian function still remain a mystery. We are unable to say what triggers ovarian activity at puberty. It is also uncertain what starts the menarche (the first menstruation) and what causes the abrupt end of egg maturation and menstrual cycling. It is believed that until puberty there is a suppression of the hypothalamic hormone called gonadotropin-releasing hormone (GnRH). GIIRH stimulates the pituitary to produces its hormones — follicle stimulating hormone (FSH) and luteinizing hormone (LH). These hormones ultimately cause the egg maturation and ovulation (the release of the mature egg from the ovarian follicle)

 As the prepubertal suppression of GnRH production is eased, FSH and LH are produced, leading to the first menstrual cycle. Slowly the functioning of the hypothalamus, pituitary and ovary becomes more integrated and regular menstrual cycles result.

The menstrual cycle

 Menstruation typically starts between the ages of ten and fifteen. Impulses in the form of hormones (GnRH) from the hypothalamus stimulate the pituitary gland to produce FSH. Under the influence of FSH, several primordial follicles start maturing but only one becomes the dominant follicle (or egg) for that cycle. The oestrogen produced by the egg stimulates a surge in the production luteilising hormone by the pituitary gland and this causes ovulation. The surge of LH causes ovulation in the middle of the cycle about fourteen days after the follicle starts growing. After the egg is released the remaining cells of the empty follicle form called corpus luteum. (Latin for yellow bodied) which then produces the second female hormone, progesterone in the menstrual cycle. In the first two weeks of the menstrual cycle leading up to ovulation estrogens help the growth of the lining of the uterus( The Endometrium). 

In the first two weeks of the menstrual cycle, leading up to ovulation, the oestrogens help the growth of the lining of the womb (the endometrium). In the second two weeks, the progesterone matures or ripens this lining.

If conception occurs, nutrition and support is provided by this lining for the growing embryo. Progesterone levels remain elevated, ensuring the stability of the womb lining, and enabling the pregnancy to continue. However, if fertilisation does not occur, an abrupt fall in oestrogen and progesterone levels takes place about 10—12 days after ovulation.

 This drop in hormone levels destabilises the lining of the womb, which is then shed as menstrual flow indicating the end of the ovarian cycle. Regular

menstruation is a reassuring visual sign that the ovarian function is normal. A new cycle of egg maturation begins.

At the time of menstruation other specific chemicals called prostaglandins are produced in the endometrium which may be responsible for period cramps, headaches, nausea and dizziness accompany a menstrual period

Regular menstrual cycles continue for thirty to forty years, the reproductive years of a woman’s life. During these years, a woman can menstruate 400—500 times. The only time when the lack of a period is normal is during pregnancy and lactation. Otherwise the absence of a period may indicate disturbances of the ovarian function.

By the age of 40 to 45 years, most of the primordial follicles are used up. There is erratic maturation of the remaining follicles and often irregular menstruation. This irregularity is usually accompanied by an overall decrease of oestrogen levels. When the oestrogen level is low the pituitary gland receives an impulse to secrete increasing quantities of FSH. This is an attempt to stimulate the remaining follicles, which are usually less responsive and fail to mature, and hence fail to produce oestrogen or progesterone.

Occasionally, ovulation can occur during these years of irregular menstrual cycles prior to menopause. However, when all the follicles are exhausted, or any that remain do not mature despite increasing amounts of FSH from the pituitary, the ovarian cycle and menstruation cease. The complete cessation of the menstrual cycle announces the onset of menopause.

 Menopause is therefore correctly dated only in retrospect by the absence of any further period. The age when it usually happens is around 50 years although there are racial, genetic and socioeconomic variations to this mean age. During the period of irregular menstrual cycles prior to menopause the blood FSH level may be high but the LH level can be normal. Women are still at risk of conceiving, although the risk is small. It is only after blood levels of FSH are shown to be consistently high that pregnancy cannot take place, and true menopausal status is confirmed.

Oestrogens

There are three main types of oestrogens — oestradiol, oestrone and oestriol.  Oestradiol is the most potent of the oestrogens. Oestrogens are mainly produced by the maturing egg follicles. In the prepubertal years, small quantities of oestrogens are produced from the ovaries before regular menstruation is established. Some of the oestrogens are derived from the conversion of androgens (secreted by the ovaries and adrenals) to oestrogens. This conversion takes place in body fat

Besides their role in reproduction, oestrogens perform several other important functions. During puberty, they help the growth of the sexual organs: the breasts, uterus, fallopian tubes, vagina and vulva. The child’s figure changes to a female figure with increased fat deposition and bone mass. Oestrogens are responsible for the distinctive female body shape because they regulate the specific distribution of the body’s fat in the hips, abdomen and upper arms. The development of under-arm and pubic hair is due to an increase in androgens from the adrenals and the ovaries. Subsequently ovulation starts and women begin their reproductive life. During a normal menstrual cycle, the oestrogen level varies from being very low just before and on the first day of menstruation, after which it starts to increase as the new follicle matures

Oestrogens help the development and maintenance of bone mass and the body’s other structural tissues such as collagen. The wellbeing of the cardiovascular system appears to be enhanced by an adequate supply of oestrogen which helps to protect women from coronary artery disease.

Progesterone

Progesterone is produced by the corpus luteum of the ovary in the second half of the menstrual cycle. It plays an important role in reproduction, and is essential for the maintenance of a pregnancy. Its main functions include the maturation of the lining of the uterus, the thickening of the cervical secretions, maturation of the cells of the vaginal lining and the relaxation of the body muscles in general. It helps the glandular development in the breasts. It can cause a slight rise in body temperature, fluid retention, acne and mood swings. These signs indicate that ovulation has taken place.Recent evidence also suggests that progesterone helps in the maintenance of bone mass and in the prevention of osteoporosis.

Androgens

Androgens (androstenedione and testosterone) are derived from the adrenal glands and ovaries. They are mainly responsible for muscular development, growth of body hair, sense of wellbeing and play a part in sexual desire. At menopause, androgens are converted to oestrogens in body fat. This conversion supplies some oestrogen to women after menopause although in a much decreased amount. Nonetheless, the presence of oestrogen from this source prevents many postmenopausal women from experiencing effects of menopause such as hot flashes, emotional disturbances and atrophy of the genital organs including the breasts. Obese women are less likely to suffer some effects of menopause as their larger supply of body fat can help in maintaining reasonable levels of oestrogens by this conversion. Of course, obesity brings with it other problems, including irregular bleeding, endometrial thickening and increased risk of cancer of the uterus.

Because of a relative excess of androgens, which are male hormones, facial hair may appear for the first time after menopause. As years go by, the acute symptoms of oestrogen-deflciency such as hot flashes abate, but the long-term effects of oestrogen deprivation such as osteoporosis, thinning and shrinking of the genital organs and adverse effects on the cardiovascular system become more significant. According to the National Heart Foundation, heart disease is the leading cause of death for Australian women, representing 24.6% of all deaths. Fifty per cent of all postmenopausal women die of heart disease.Eventually, the ovary is exhausted and does not produce even enough androgens to be converted to oestrogens. The contribution made by the adrenal gland proves inadequate; consequently the effects of oestrogen deficiency become more and more severe.

Changes to expect around and after menopause           

The ovary at menopause shrinks to the size of an almond. Opinions differ about the number of remaining follicles at this stage: from a few hundred to none. The follicles do not respond to increasing quantities of FSH. Small amounts of oestradiol may still be produced, but this is about one tenth of the amount produced during the menstrual cycle. The ovarian stroma increases its secretion of androgens due to the stimulation from increased FSH levels. Some of these androgens are converted to oestrogens in menopausal women. These oestrogens (predominantly oestrone) are not as potent as the oestradiol secreted by the maturing follicles.

 The pituitary produces increasing amounts of FSH and LH — up to five times more than during the reproductive years. After a certain point, there is no further increase. Androgen levels may be relatively high compared with oestrogen levels. The total cholesterol level in the blood is increased and the ratio of low—density (‘bad’) cholesterol to high—density (‘good’) cholesterol increases, raising the risk of heart disease. There is also new evidence that the absence of oestrogen adversely affects the tone of the arterial walls.

Calcium balance is also adversely affected, causing thinning of the bones and osteoporosis. Consequently the risk of fractures increases. The breasts may change in size. In some women, the size increases from fat deposition. Such fat deposition takes places in other parts of the body particularly the abdomen, hips and arms which then causes a change in body shape and weight distribution. Meanwhile, the uterus decreases in size and the lining thins out. The cervical secretion decreases. The vagina becomes thinner and smaller. It loses its elasticity, lubrication and acidity. During the reproductive years, the acidity of vaginal secretions helps prevent vaginal infections.

The external genitalia (the vulva) undergoes thinning. However the pad of fat on top of the pubic bone called the mons pubis often gets thicker from fat deposition. Pubic hair becomes sparse. Sexual desire in some women increases due to high androgen levels, while in others, it decreases as a result of pain during sexual intercourse, caused by a dry vagina.

Key points

1.     The ovary, the female sex gland, is the main organ concerned with menstruation, reproduction, production of the female hormones cestrogen and progesterone, and menopause.

2.     The ovary lies dormant from birth to puberty and becomes dormant again at menopause, after four decades of reproductive activity.

3.     It is now being researched what biological catalysts activate, and then end, ovarian activity. Further to this key point, in 1990 a neuron called kisspeptin was discovered in Hershey(Pennsylvania) it is named after the Hershey’s Kisses (Chocolate Bars), so that everybody will know where it was discovered. In the last ten years lots of research has been done on Kisspeptin and it has been concluded that Kisspeptin neurons joined to GPR54 are singularly essential to initiate gonardotrophrin secretion at puberty. They are essential at the start of puberty but they do not control when the puberty starts. Originally this gene was responsible for the suppression of the spread of melanoma in breast cancer. It is now a very useful tool in the management of infertility and IVF.

4.     Oestrogens play the key role in maintaining a woman’s health during the reproductive years. The lack of oestrogens may cause complex physical and emotional problems often associated with the menopausal years.