The menstrual cycle is an integral part of this reproductive function. It is called menses and it is derived from the Latin word meaning monthly.
The main organs involved in this monthly cycle are Hypothalamus and Pituitary and they are located in the brain. The main female sex gland is called the ovary and it is located in the abdomen close to the uterus and the two tubes. The uterus is connected to the outside world by the cervix and the vagina. The chemicals produced by the hypothalamus and pituitary glands are called hormones which in turn act on the ovary which produces its own hormones. They help in the maturation of the egg and preparation of the uterus to receive the egg if fertilised.
If the pregnancy does not occur the prepared lining of the uterus is shed causing bleeding and this is called menstruation.Usually the menstruation starts around the ages of ten to fourteen years, and lasts for forty years in a women's life. The menstrual bleeding lasts three to seven days and blood loss is about 30 - 50 mls. The cycle usually varies between twenty-one to thirty five days.
It is only recently that we have started to understand what triggers the menstrual cycle.
They have found a new chemical called Kisspeptin which is supposed to trigger the hypothalamus to produce a hormone called 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.
Under
the influence of FSH, several primordial follicles start maturing but only one
becomes the dominant follicle for the cycle.
The growing egg produces oestrogens,
The oestrogens produced by the egg
stimulate a surge in the production of another hormone LH by the pituitary gland. This surge in
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 turn into what is
called the corpus luteum (Latin for ‘yellow body’) which then produces the
second of the female hormones, progesterone, in the second half of the
menstrual cycle. 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.
Menstruation
is a reassuring 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 which can accompany a menstrual period.
Key points
1.
The ovary, the female sex
gland, is the main organ concerned with menstruation, reproduction, production
of the female hormones oestrogen 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.
4. Oestrogens play the key
role in maintaining a woman’s health during the reproductive years.
5. There are many issues about menstruation that need to be discussed, such as;
A-Puberty, B-Amenorrhoea,(No Periods), C-Premenstrual tension(PMT),D-Painful Periods,
E-Heavy and Irregular Bleeding, F-Polycystic Ovaries, G-Contraception.
All these problems will be discussed in future posts.
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